Laser Science And Applications: Proceedings of the 6th Intl Conf Natl Inst of Laser Enhanced Sciences, Cairo Univ, Egypt 15-18, January 2007

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LASER SCIENCE AND APPLICATIONS PROCEEDINGS OF THE SIXTH INTERNATIONAL CONFERENCE

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LASER SCIENCE AND APPLICATIONS PROCEEDINGS OF THE SIXTH INTERNATIONAL CONFERENCE NATIONAL INSTITUTE OF LASER ENHANCED SCIENCES CAIRO UNIVERSITY, EGYPT 15 - 18 JANUARY 2007

edited by Lotfia M. EI-Nadi & Mohy S. Mansour Cairo University, Egypt

,~World Scientific NEW JERSEY· LONDON· SINGAPORE· BEIJING· SHANGHAI· HONG KONG· TAIPEI· CHENNAI

Published by

World Scientific Publishing Co. Pte. Ltd. 5 Toh Tuck Link. Singapore 596224 USA office: 27 Warren Street. Suite 401-402. Hackensack. NJ 07601 UK office: 57 Shelton Street. Covent Garden. London WC2H 9HE

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LASER SCIENCE AND APPLICATIONS Proceedings of the Sixth International Conference Copyright © 2010 by World Scientific Publishing Co. Pte. Ltd. All rights reserved. This book. or parts thereof, may not be reproduced in any form or by any means. electronic or mechanical, including photocopying, recording or any iliformation storage and retrieval system now known or to be invented. without written pennission from the Publisher.

For photocopying of material in this volume. please pay a copying fee through the Copyright Clearance Center. Inc .• 222 Rosewood Drive. Danvers. MA 01923. USA. In this case permission to photocopy is not required from the publisher.

ISBN-13 978-981-281-459-3 ISBN-IO 981-281-459-0

Printed in Singapore by B & Jo Enterprise Pte Ltd

FOREWORD

The National Institute of Laser Enhanced Sciences (NILES) Cairo University is one of the centers of excellence in the Middle East and Africa. NILES is located at Cairo University campus near the great river Nile and about 9 km from the great pyramids of Giza. The International Conference of Laser Sciences and their Applications, ICLSA-07, is the 2007 biannual conference organized by NILES. ICLSA has attracted many international participants during the last five conferences since the foundation of NILES in 1994. The main topics of ICLSA-07 are the basic researches focused on laser sciences and the applications in many fields. It is also opened to new technologies that are related to laser science, e.g. bio- and nano-technologies. The sixth international conference on laser sciences and applications, ICLSA-07, continues the success of the previous ones. It has attracted many scientists from countries all over the world. We were proud to invite eminent national and international scientists to provide great contributions to ICLSA-07. The warm atmosphere at NILES allows the integration and cooperation between our young and senior scientists and international participants. During this conference we were able to announce the foundation of the Arabic Society of Advanced Laser Applications, AS ALA. The main goal of ASALA is the unification of scientists from Arab world in the field of laser science and applications to apply and develop this field for some problems of common interest. NILES is proud to continue this biannual meeting ICLSA and to integrate many related areas and provide some facilities and ideas for joint research projects.

Conference Chair Mohy Mansour Dean of NILE

v

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PREFACE

The International Conference on Laser Science and Applications held between 15-18 January 2007 (lCLSA-07) is the sixth conference held at the National Institute of Laser Enhanced Sciences (NILES) in Cairo University. Lasers and their uses are the most dominating fields of research in the 21 st century. The technical program featured three topics comprising basic and applied fields in the laser world: • • •

Topic I Basics of Laser Science Topic II Laser Applications in Engineering Topic III Laser Applications in Medicine

•

Topic I: Basics of Laser Science

It included subjects that were classified into: generation of attosecond high

harmonic laser pulses and their characterization, which has been explained basically by the distinguished Prof. Dr. Chang Hee Nam, Director of the Korean Coherent X-ray Research Center CXRC at the Physics Department of the Korean Advanced Institute of Science and Technology (KAIST) at Daejon. Such method points to this important field as the promising way of achieving x-ray laser technology. Types of high power lasers and their use in machining of metals were discussed by Prof. Dr. Chatwin from the University of Sussex. Professor Dr. Lotfia El Nadi, initiator of NILES with her vision on important future fields of laser science, speculated with Prof. Mohy Saad, Dean of NILES, the prospectives of ultrahigh power short pulse lasers and their present and forthcoming use as laser accelerators, pointing out the possibilities of upgrading the existing facilities at NILES, with her student M. Atef Reda. She and her school discussed the use of optical forces to manipulate atoms. Professor Yehia Badr, ex-Dean of NILES, and his school presented their results on some optical materials as promising new active laser media. Automated stabilization and optimization of laser beams were included as well as studies on propagation of lasers in air and inert gas mixtures.

vii

viii

•

Topic II: Laser Applications in Engineering

The presentation by Prof. R. Salimbeni, the famous Italian archeology scientist, dealt with the applications of laser technology in the field of conservation of artworks, putting in mind Egypt as the host of the most ancient archeological monuments. Technology aided conservation of building heritage using methods for 3 dimensional visions were discussed . Simulation and engineering of resonators, optical materials and design of some optical digital circuits as important research results were also included. Laser applications in engineering introduced versatile subjects.

•

Topic III: Laser Applications in Medicine

It is a topic that delivered detailed scientific information on one of the most important subjects of laser applications namely: Laser applications in medicine and biology. The subjects discussed could be summarized as photo induced effects on bacterial cells, with detailed results on normal and leukemic peripheral blood cells. The method applied by Prof. Dr. Mohamed EI Batanouny and his school using photosensitizers points to highly important ways of utilizing laser technology in the medical field. Professor Dr. B. Kramer, a pioneer scientist in her field , introduced the international community to the promising field of molecular mechanisms and aptosis in photo dynamic therapy . The students of Prof. Mohamed Abdel-Harith, ex-Dean of NILES , surveyed the laser application techniques in follow up of metal toxicity in some important botanic species. The presentations of some distinguished international invited lecturers have not been included in this proceedings, but we have to acknowledge their efforts in presenting their fields of research . In the following , arranged in alphabetic order of the names of the contributors, we present the titles of their talks delivered during the sessions of this conference: I. Elizabeth Giacobino, Ecole Normal Superieure & CNRS, France. Quantum Optics & Quantum Communication. 2. Hilal A. Fattah, Atomic Energy Authority, Egypt. Quantification of Heavy Metals in New Materials by Laser Ablation . 3. Jai Pal Mittal, Bhabha Atomic Research Center, India. IR Laser Multiphoton Dissociation.

ix

4. Mahmoud H. Abdelkader, German University, Egypt. Laser PDT: Oncological and Nononcological Applications 5. Mohy S. Mansour, Cairo University, Egypt. Laser Diagnostics for Combustion Systems. 6. Mohamed Raafat EI Gewely, University of Troms¢, Norway. Gene Reconstruction and Transfection for Cell Engineering. 7. Mostafa EI Sayed, Georgia Institute of Technology, USA. Nanogold Technology in Laser Cancer Therapy. 8. Mushera Salah EI Din, Cairo University, Egypt. Laser Technology in Dentistry. This proceedings highlights the main contributions that were presented and provided by the excellent authors in a perfect and timely manner. I would like to express my sincere thanks to the Authorities of Cairo University specially Prof. Dr. Ali Abdel Rahman the President and Honorary Chairman of the conference, the Atomic Energy Authority of Egypt, the German University in Egypt, the International Arab Company for Optical Materials and the Topical Society of Laser Sciences for their generous financial support without which the conference would not have been possible. I am greatly indebted to Prof. Dr. Mohy S. Mansour, Chairman of the conference and Dean of NILES for his encouragement and support which greatly helped to shape and accomplish the ICLSA-07 conference. Utmost thanks to be stated to Engineer Dr. Jala EI-Azab and Biologist Dr. Rehab Amin for giving celibacy efforts and facilities for mass communication, computational activities and information transfer. Without their efforts this book would not be have been accomplished. In conclusion, it is worthwhile to mention the main annotations taken by the participants who attended the closing session that was held on 18 th January 2007. FIRST: They proposed establishing a society by the name ASALA to strengthen the scientific and social relations between the Arab countries for researchers working in laser application fields. SECOND: Interaction between participants was excellent since plenty of time for discussions was available and social cultural atmosphere was developed. THIRD: More young research students should be encouraged to attend such conference and well studied projects should be designed and ready to forward and implement international cooperation with the International participants.

x Finally, I would like to thank all who, directly or indirectly, have helped to accomplish this proceedings. In years to come, I will devote my time and energy to further establish possibilities for Egyptian laser scientists to be involved in the fascinating world of high technology.

Prof. Dr. Lotfia M. EI Nadi Program Chair of ICLSA-07 Vice Director of International Centre of Scientific and Applied Studies of HDSP Lasers (IC-SAS) - NILES, Cairo University Prof. of Nuclear Laser Physics, Physics Department, Faculty of Science, Cairo University, Egypt

CONTENTS

Foreword ...................................................................................................... Preface .......... ........... .....................................................................................

v vii

1- LASER SCIENCE 1-1. KEYNOTE AND PLENARY PAPERS

Attosecond High Harmonic Pulses: Generation and Characterization C. H. Nam and K. T. Kim High Power Lasers and Interactions .... .............. ......... ................... ..... ...... ..... C. Chatwin and R. Young

3 9

1-2. INVITED LECTURES

Laser Accelerators ........................................................................................ L. M. El-Nadi, M. S. Mansour, G. Abdellatif and M. A. Reda

19

1-3. CONTRIBUTED PAPERS

Energy Levels, Oscillator Strengths, Lifetimes, and Gain ............................ Distributions of S VII, CI VIII, and Ar IX Wessameldin. S. Abdelaziz and Th. M. El-Sherbini The Gain Distribution According to Theoretical Level Structure and .......... Decay Dynamics of W 46+ H. M. Hamed, Wessameldin. S. Abdelaziz, A. Farrag, M. Mansour and Th. M. El-Sherbini Raman Spectroscopy and Low Temperature Photoluminescence ZnSe xTe I-X Ternary Alloys A. Salah, G. Abdel Fattah, Y. Badr and I. K. Elzawawy Automated Polarization-Discrimination Technique to Minimize ................. Lidar Detected Skylight Background Noise, Part I Y. Y. Hassebo, K. Elsayed and S. Ahmed Laser Interferometric Measurements of the Physical Properties for ............. He, Ne Gases and their Mixture N. M. Abdel-Moniem, M. M. El-Masry, B. El-Bradie and F. M. El-Mekawy

xi

33

53

67

85

97

1-4 POSTERS Analytical Studies of Laser Beam Propagation through the .... .. .. ................ . Atmosphere M. I. El-Saftawy, A. M. Abd El-Hamed and N. SIz. Kalifa

113

11- LASER APPLICATIONS IN ENGINEERING II-1. INVITED LECTURES Laser Techniques in Conservation of Artworks: Problems and .. .... ...... ........ Breakthroughs R. Salimbeni and S. Siano

129

11-2. CONTRIBUTED PAPERS Technology-Aided Heritage Conservation Laser Cleaning for .................... 143 Buildings M. S. Nada Technology Significance in Conservation of the Built Heritage 3D 157 Visualization Impact M. S. Nada Simulation of Optical Resonators for Vertical-Cavity Surface-Emitting 171 Lasers (VCSEL) M. S. Mansour, M. F. Hassen, A. M. El-Nozahy, A. S. Hafez and S. F. Metry Optical Design Alternati ves: A Survey Study.............. ........................ ........ 185 A. A. K. Ismail, I. A. S. Ismail and S. H. Ahmed Materials for Digital Optical Design; A Survey Study........................ ......... 197 A. A. K. Ismail, I. A. S. Ismail and S. H. Ahmed Proposed Design for Optical Digital Circuits.......... ............................ ......... 211 A. A. K. Ismail, I. A. S. Ismail and S. H. Ahmed

111- LASER APPLICATIONS IN MEDICINE III-I. CONTRIBUTED PAPERS Photo-Induced Effect on Bacterial Cells ...................................................... M. H. El Batanouny, R. M. Amin, M. I. Naga and M. K. Ibrahim

xii

223

xiii

Laser and Non-Coherent Light Effect on Peripheral Blood Normal and ...... Acute Lymphoblastic Leukemic Cells by Using Different Types of Photosensitizers M. H. El Batanouny, A. M. Khorshid, S. F. Arsanyos, H. M. Shaheen, N. Abdel Wahab, M. N. El Rouby and M. I. Morsy Molecular Mechanisms and Apoptosis in PDT ............................................ B. Krammer and T. Verwanger Follow up of Treatment of Cadmium and Copper Toxicity in Clarias Gariepinus Using Laser Techniques K. H. Zaghloul, M. F. Ali, M. G. A. El-Bary and M. Abde/-Harith

235

255 261

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I - Laser Science 1-1. Keynote and Plenary Papers

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ATTOSECOND HIGH HARMONIC PULSES: GENERA TION AND TEMPORAL CHARACTERIZATION· CHANG HEE NAM AND KYUNG TAEC KIM Department of Physics and Coherent X-ray Research Center, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Korea

A method to obtain near transform-limited attosecond harmonic pulses is presented along with techniques to characterize attosecond pulses, especially complete temporal reconstruction of attosecond pulses based on the frequency-resolved optical gating algorithm.

1. Introduction Atoms driven by intense femtosecond laser pulse emit high harmonics in the xuv/soft x-ray wavelength region [1] . The high harmonic light source can provide an attosecond pulse train or a single attosecond pulse when properly controlled [2]. Because of its short duration, it is a valuable tool not only for the study of the ultrafast phenomena but also for understanding high harmonic processes in atom and molecules [3,4]. The attosecond pulses obtained from high harmonic generation (HHG) contain a complex chirp structure [5, 6]. In single-atom calculations, the attosecond pulses, originating from the short quantum paths formed in the leading edge of the laser pulse, are positively chirped, resulting in longer pulse duration than that of the transform-limited pulse [5]. Since the positive chirp in the time domain corresponds to the positive second-order dispersion in the spectral domain, it can be compressed by passing through a material having negative group delay dispersion (GDD). Some x-ray filter materials have such negative GDD, and it has been shown that single sub-SO-as pulses can be generated from neon atoms by using 700-nm-thick Sn filter by Kim et al. [5]. Experimentally 170 attosecond pulses were generated from Ar harmonics by using a 600-nm-thick Al filter by Martens et al. [7]. Since the material for the attosecond pulse compression need not to be a solid material, a gaseous medium • This research was supported by the Ministry of Science and Technology of Korea through the Creative Research Initiative Program.

3

4

also can be applied. In fact, some rare gases, commonly used for the harmonic generation such as Xe, Ar, and Kr, have such negative GDD spectral region. When these gases are used for harmonic generation, the pulse compression may occur during harmonic generation without using an additional material. Temporal characterization of attosecond pulses is still challenging task since efficient nonlinear material for two photon processes is difficult to realize in the xuv wavelength region. Autocorrelation techniques, widely used for the characterization of femtosecond pulses, can be applied only to limited cases of low-order harmonic pulses [8]. Cross correlation techniques, based on the photoionization by high harmonic and femtosecond laser pulses acting simultaneously, are thus valuable for the characterization of attosecond harmonic pulses [9, 10]. In this proceeding, a method to generate near transform-limited attosecond harmonic pulses is presented along with techniques to characterize attosecond pulses. The reconstruction of attosecond beating by interference of two-photon transition (RABITT) technique [9] is used for the chirp characterization and the estimation of pulse duration. For the full temporal characterization of attosecond pulses, the frequency-resolved optical gating for complete reconstruction of attosecond bursts (FROG CRAB) technique is also reported [10].

2. Temporal characterization of transform-limited attosecond pulses using RABITT For the temporal characterization of complex harmonic pulses, one needs to precisely determine the spectral phase and amplitude of the harmonic pulses. In the RABITT method, the photoelectron spectra obtained from attosecond harmonic pulses with probe laser pulses are used for the reconstruction [9]. The photoelectron spectra show sidebands due to the interference of the electron wave packet ionized by two-photon transition. The sidebands are modulated with the time delay between harmonics and the laser. The phase information of the attosecond harmonic pulses can be found from the side band modulation: (1)

Here, A is the amplitude of the modulation, liJo is the laser frequency, T is the time delay between harmonics and the laser, I1rpq is the phase difference of the (q+l)th and the (q_l)th harmonics. The spectral amplitude information can be found in the photoelectron spectrum without the laser field. The reconstruction of the attosecond harmonic pulses is possible from the phase and amplitude information.

5 Ar

Laser forHHG

Difterential pumping Holed mirror

Gas cell

t

Probe beam

TOF target (He)

Figure I. Schematics of the experiment setup. (TOF: time-of-flight electron spectrometer)

A I-kHz Ti:sapphire laser, generating pulses of 30-fs duration, was used to obtain high harmonics, as shown in Fig. 1. The laser beam was split into two parts by a beam splitter. The first beam was focused into the middle gas cell for HHG. The second beam was used as a probe laser beam. After harmonic generation, the transmitted laser beam was blocked by a 200-run aluminum filter to completely eliminate the laser light. The harmonic and the probe beams were combined using a mirror having a hole in the center and both beams were then focused together, using a gold-coated toroidal mirror, into a time-of-flight photoelectron spectrometer. For the RABITT measurements, the attosecond harmonic pulses were generated with 2.5xI014W/cm2 laser in I2-mm-long 40-torr argon gas cell. First, the spectral amplitude of harmonics was obtained from the photoelectron spectrum of helium gas without using the probe beam. The photoelectron distribution was measured from I7ili. to 41 sl harmonic orders. In this case, the lower harmonics were severely absorbed (filtered) and the intrinsic positive chirp was compensated by the negative group delay dispersion of the argon medium itself. From the RABITT measurements, temporal profiles of attosecond harmonic pulses were reconstructed, as shown in Fig. 2. The full width at half maximum (FWHM) of the attosecond harmonic pulse was 206 as, very close to the transform-limited pulse width of 200 as.

6

,.-.. 1.0 en .....

'§ 0.8

..0 a 0.6 '--'

.c 0.4

'00

~ 0.2 .....

s=

...... O.O+---~

-600

-400

-200

0

200

400

600

Time (as) Figure 2. Reconstructed self-compressed attosecond harmonic pulses using RABITI technique.

3. Complete temporal characterization of attosecond harmonic pulses The FROG CRAB method is an improved version of the RABITT technique, in which a 2-dimensional phase retrieval algorithm is used for the reconstruction. In the RABITT technique, each harmonic is assumed to be a plain wave [10]. Due to this assumption, it cannot be used for the reconstruction of the single attosecond pulse, having continuum spectrum. Also, the reconstruction result is always infinite pulse train, providing only averaged temporal characteristics of a real pulse train. As a consequence the chirp information of each harmonic is not available. The FROG CRAB, on the other hand, has no such drawback, allowing the complete temporal information of attosecond pulses. For example, we can look into such issues as the duration and chirp structure of individual pulses in the attosecond pulse train and the harmonic frequency change in time with respect to harmonic order. This kind of information can be clarified from the FROG CRAB analysis. In this technique, the photoelectron spectra obtained by applying harmonic and laser pulses together with time delay T can be represented by (2)

Here Ex (t) is the harmonic electric field to be measured and G( t) is the phase gate function, defined by (3)

7

where v is electron velocity and A (t) is the vector potential of femtosecond laser field. Since Eq. (1) is the spectrogram expressed in frequency and time delay, a conventional FROG inversion algorithm, such as the principal component generalized projection algorithm (PCGPA), may be used to reconstruct attosecond harmonic pulses [11]. Consequently, one can retrieve the harmonic electric field.

1.0

"-- - --- - ____-Ixuv(t)

-

----------IA(ll"fJ

~ 0.8

§ 0.6

~"_ ;: 0.4 _x 0.2 0.0

~----~----~----.---~10 5 o -5 -10

Time (fs) (b)

Figure 3. (a) Photoelectron spectra obtained from 20-torr argon with the probe laser beam. (b) The reconstruction of the attosecond harmonic pulses using FROG CRAB technique.

FROG CRAB measurements were carried out using the same experimental setup as shown in Fig. 1, but with the different harmonic conditions due to the poor energy resolution of the spectrometer at the high energy region. The attosecond harmonic pulses were generated in a 6-mm-Iong 2S-torr argon gas cell up to the 31 sl harmonic order. In this case, the photoelectron spectra were obtained for the full range where harmonic pulses and probe pulses were overlapped, as shown in Fig. 3(a). The temporal reconstruction of the harmonic

8

pulse, with orders higher than 17 th that generate photoelectrons in He, was performed using the PCGPA algorithm. Figure 3(b) shows the reconstructed temporal profile of the harmonic pulse. The envelope width of the pulse train is 11 fs and the width of the attosecond pulse at the center of the train is 230 as. In this case, the intrinsic attosecond chirp at the center of the train is estimated to be 1.4xlO·32 S2, and the harmonic chirp of the 17 th order is _2.3xl0- 28 S2. Since the PCGP A is a blind FROG technique, not only the harmonic pulse, but also the laser field information is available. By comparing both fields, one will be able to obtain the information on ionization dynamics during the high order harmonic generation processes. 4. Conclusion We have demonstrated self-compressed attosecond pulse generation with the pulse duration of 206 as, very close to the transform-limited value of 200 as. For the full temporal characterization of attosecond harmonic pulses, the FROG CRAB technique has been demonstrated. The attosecond pulses of II-fs envelope width and 230-as pulse width at the center of the attosecond pulse train were measured. References 1. M. Hentschel et aI., Nature 414,509 (2001). 2. Ph. Antoine, A. L'Huillier, and M. Lewenstein, Phys. Rev. Lett. 77, 1234 (1996). 3. T. Kanai, S. Minemoto, and H. Sakai, Nature 435, 470-474 (2005). 4. R. Kienberger et aI., Nature 427,817 (2004). 5. K. T. Kim, C. M. Kim, M.-G. Baik, G. Umesh, and C. H. Nam, Phys. Rev. A 69, 051805(R) (2004). 6. H. J. Shin, D. G. Lee, Y. H. Cha, K. H. Hong, and C. H. Nam, Phy. Rev. Lett. 83, 2544 (1999). 7. R. Lopez-Martens et aI., Phys. Rev. Lett. 94, 033001 (2005). 8. T. Sekikawa, A. Kosuge, T. Kanai and S. Watanabe, Nature 432, 605 (2004). 9. P. M. Paul, E. S. Toma, P. Breger, G. Mullot, F. Auge, Ph. Balcou, H. G. Muller, and P. Agostini, Science 292, 1689 (2001). 10. Y. Mairesse and F. Quere, Phys. Rev. A 71, 011401(R) (2005). 11. D. J. Kane, IEEE J. Quant. Elec. 35,421 (1999).

HIGH POWER LASERS AND INTERACTIONS PROFESSOR CHRIS CHATWIN AND DR RUPERT YOUNG

University ofSussex, School ofScience and Technology, Brighton BN I 9QT, UK Email:[email protected]. uk

Abstract When high intensity laser radiation interacts with a metallic surface the photon flux is absorbed by Fermi surface free electrons, these collide with lattice phonons transferring the laser energy into the target material. Below a threshold irradiance this energy transfer mechanism remains in equilibrium and can be described by Fourier conduction; above this threshold the electrons are not in equilibrium with the lattice, this controls the development of the surface plasma which controls the way energy is coupled into the target; which determines the type of process that ensues.

Introduction When high intensity laser radiation is delivered in a pulse with a rapid rise time the photons are mainly absorbed by the free electrons above the Fermi surface, the subsequent rate of energy transfer from electrons to phonons is too slow for thermal equilibrium to be maintained between the electrons and the lattice. Photons are absorbed by electrons, whose temperature rises extremely quickly and follows the temporal shape of the laser beam pulse. The phonons are too slow to respond significantly to the incident radiation. Hence the temperature of the Fermi surface free electrons is different from the phonon temperature; the magnitude of this temperature difference depends on the incident laser power and the rate of energy transfer between the electrons and the phonons. The mean free path for electron-electron collision is several orders of magnitude greater than that for electron-phonon collisions; hence, electron-electron interaction can be neglected.' The thermally excited electrons collide with lattice phonons giving up a proportion of their energy in each collision; this is the main energy transfer mechanism that is responsible for heating of the lattice. Via Umklapp processes the phonons transfer energy very rapidly to the lattice to attain local equilibrium in any given region.' For fast rise time pulses Fourier conduction theory produces erroneous predictions of performance, Figure(8) illustrates the magnitude of this difference in predicted temperature rise. The Kinetic theory predicts that most of the energy will be contained within a thin surface layer; the laser/material interaction is dominated by non-equilibrium energy transfer processes. This paper develops a Kinetic theory and reports some results using this theory, these results are compared with some experimental results which were obtained by irradiating metal targets with an Nd3+:Glass laser. The target material surface temperature was measured using a two colour temperature measurement technique. Kinetic theory model Referring to Figure (1), we need to evaluate the number of electrons which leave element 'dE' after colliding there, then suffer their next collision in a volume element 'dV' a distance's' away in time 'dt'. The solid conical element subtends an angle 'dOl' with the 'x'. We need to take account of electrons coming from the right of'dV' and electrons that are reflected from the surface and travel along the path 'SAC'. To achieve this we can use a mirror image method as shown in figure (2).

", ,

,, ,,

,,

, ,,

,, dro "''' ...

I:

,

E

:.

...

d'ro"

'~:~~,

dE

I

'~ ~-

v

.r

,(----+ B

' ....

I

"::~';'

. : :;: '3

I:

,

" "

'~

"\,

dV

WI',",

E

'

... __ _ ..I

,

, I

.-----------~----------~

: C

0"" - - - - - - - - - -x- - - - - - - - - +i

x=o

Figure (I) Schematic illustrating electron movement inside metals

Figure (2) Schematic illustrating electron movement inside metals Using a mirror image method

9

10 Using the mirror image method we must determine the energy transported into 'dV' from all electrons in 'dE' at 'E'

N'z.rdwe(-s(A) ds.dV 2s

(I)

ACOSW

Where: N' = number of Fermi surface electrons;)., = electron-phonon mean free path; z = collision frequency in dV; v = Fermi electron velocity; z = v /).,. Hence to evaluate the number of electrons arriving in 'dV', which come from 'dE', we must integrate over <<Xl' and '0 < (J) < ,,/2'

'-00

<E

The energy carried into the volume 'dV' in time 'dt' by electrons depends upon the specific time at which the electron free path was generated. There are two groups: i)

Those travelling a distance's < vdt'. Electrons generated within the time interval 'dt' will arrive in 'dV' during the same time interval.

ii)

Those travelling a distance's 0: vdl'. These electrons must be generated in the previous time intervals if they are to arrive in 'dV' during the current 'dl'.

Therefore the average energy 'E' stored in an electron at 'E' is:

E = E(s,t) + .!.{dt _~} GE(s,t) 2 V ot

(2)

Ignoring quantum effects, free electrons are assumed to acquire the laser energy by merely passing through the electromagnetic field of the incident beam. The field is described by Lamberts law:

I(x,t) = 1 0 (1- R(t))e(-<5x)

(3)

Where: 'I(x,t)' is the beam intensity at time 'I' after propagating distance 'x' in the material. 'Io(t)' is the intensity at the surface. 'R(t)' is the reflection coefficient and '0' is the absorption coefficient. Considering the small element 'dp', figure (3); the power absorbed per unit area by electrons at time 'I' is:

10 (t)(1- R(t))&/ -bp) dp

(4)

The energy absorbed per electron is:

10 (t)( I - R (t)) <5 e ( - <5P ) dp IJ. t

(5)

N' Where' 1J.t' is the average time an electron stays in the element' dp';

LJt

=

dp / vcosw

(6)

It can be assumed that 'Io(t)' and 'R(t)' are constants in the time required for the electrons to move from 'E' to 'x'. Hence, substituting for' IJ.!' and integrating. The energy absorbed per electron in moving from 'E' to 'x' is:

IO(l-R)S x (_~)

-"---I Je N'v cos OJ

£

dp 1

(7)

11

dr,

-"-~

,

n

!

I

.~

t+DE

.. - - - - - - -~ ====t--(~x=O

--------~:

Figure (3) Schematic to show the photon absorption process from

E

dV

to x

From (2) and (7) the average energy of an electron entering 'dV' at 'x' from 'c' after 'dl' is:

I{

2 I S I }OE(c,{) I O(1-R)o X (_A~) E(c,t)+- dt--- - - - + I Ie "if dpi 2 v N'vcosOJ c

(8)

at

If 'Ep(x,t)' is the average energy of phonons in 'dV' at 'x', the energy given up by electrons to the phonons on collision is: f ( E(x, t+dt) - Ep(x,/)}

(9)

Where 'f ' is the fraction of the energy difference between an electron and a phonon given up by an electron on collision with a phonon. The fraction 'f ' of the average energy difference between electrons and the lattice in any given volume is':

f(X,t)=~{I3M

T(X , t)} Te(x,t)

(10)

Where 'm ' and 'M' are the masses of the electrons and lattice atoms respectively, 'T,(x,t)' and 'T(x,t)' are their temperatures at time 'I' and distance 'x', respectively. The total energy transferred to the lattice from all electrons colliding in 'dV' at 'x' over the time interval 'dl' is equal to the energy increase of the lattice, where 'n(x,t)' is the number density of atoms: anE

(x,!) 00 tr12{ P dV= dV! ! ~.e(-lx-ellAc05(v)~ } at _ 00 0 2,1 A cos 10 X

J

(j)x {E(e, I) + ~ {dl _~} aE(e, t) + 10 (1- R)S I e( -Sp) dp I v

2

al

N' v cos 10

-Ep (x,!)} dIOde

(II)

e

The average energy change of electrons at 'x' equals the energy left in the electrons after collision, less the energy carried away by electrons leaving the elemental volume 'dV' during 'dl' aN' E(x,t) dV at {E

(0,1

-dV

)

= dV

J tr f2{~)_1 _

+2'1 {dI -2-vS-

anE (x. I) P al

0

00

I

I

X-ell Acosw)

2,1

}aE(o,t)

--a-I-+

~}x A cos (0

IO(l-R)Sl x! (-oP)d

N'vcosw

e

P

I }dmdo

o

dV~E(x./) A

(12)

12

We also need the continuity equation for electrons:

(13)

Assuming that the electron gas is in a state of equilibrium, the participating electrons can be obtained from the ordinary Fermi distribution function:

NT lr 2

N,= __ e_

(14)

2TF Where: TF is the Fermi temperature, T, is the electron temperature, N is the number density of valency electrons. The thermal conductivity 'K' of the material can be shown to be:

K = N'VAk

(15)

3 The heat capacity is:

p C

(16)

p = 3nk

Where 'k' is the Boltzmann constant, 'p' is the material density, 'C,' is the specific heat and 'n' is the phonon atoms number density . Expressing the equations in terms of electron and phonon temperature. Using equations (14), (15) and (16) in (II), (12) and (13) we get:

~ [pC at

J

p

T] =

7~lrf2{e(-IX-eIIACOSIV) cosm sinm}X\T (e,t)+~ {dt_~} aTe(e,t) -T(x,t)}dmdfi e v at

_004,13

0

2

+J 10 (\-2R)O 2,1

frr::: }= <1- f)

7 00

lr?{e<-lx-ellAcosm) sin m },1e<-OP)dP' dmdfi 2 0 cos m fi

7~lrf2{e<- l x-ellAcosm)

- 00 4,13

0

+J

7

(17)

sinm}X\T
OOJ _9K lrJ/2{e<-lx-fiIIACOSW) sinm} T( E:, t)dmdE: -00 4,13 0 cos m

+J 1o (l-2R)O lr(2{e<-IX-E: I/ACOSm ) sin2m 2,1 _ OCJ 0 cos IV

}I

le<-bP)dp E:

I dlVdE:-~T

<x,t)

2,12 e (18)

aK at

OCJlr/2{K . } dmdE:- Kv J J _v_ e(-Ix-ell Acosm) SInm A 0 2,12 cosm

-OCJ

(19)

13

Incorporating Evaporation: Von Allmen 4 derived the evaporation rate using the theory of Landau 5, while Prokhorov' derived an expression based on the Clapeyron-Clausius equation, both expressions are based on continuum thermodynamics. The model used here is that due to Frenkel'. It is based on statistical thermodynamics and leads to the rate of evaporation being given by:

(20)

Where: ' n' ~ the atom number density at the surface, ' m' ~ mass of the atom, 'U o' ~ latent heat of vaporisation per atom, T, is the surface lattice temperature. The velocity of the evaporating surface 'Vs' is given by:

G=V

(21)

s

At the surface there is a mathematical singularity, this can be handled by changing the coordinate system such that the material moves with velocity 'V s ' towards the origin. The problem is then to determine the energy transported into 'dV' at 'x' from all electrons in 'dE' at 'E', then integrate for 'E' to allow for contributions from the whole of the material, bearing in mind that the bulk material is moving through the coordinate system with velocity 'Vs', see figures (4) & (5).

Group II

,, ,,

•,

Vs

Group I

~

dr

Moving Boundary

" OJ

~

...

,,

'""...=

, " ."

,,

,.."

3 " ~

r

....... ....

,, ,, ,, , , dE '., ,,.-

,

.'

)-+/"::.

...

I+----,X(""l

.... Vapour

A~---~--"" B

o

: C

O~------------------------~ . X Figure (4) Schematic illustrating electron movement inside metals, the material is moving with velocity Vs

Figure (5) Schematic of one dimensional moving boundary problem

As 'Vs « v' we can neglect the effect of material movement on electron transport. The convective heat transfer due to the moving material alters the equations describing the lattice and electron energy distributions

ata [pC pTl-Vs axa [pC /1 ~ f 00J -9K -00

4A3

ff J 12{ e(- l x-c llA coSlV) SlnlV . } x \Te(C, I. 2 1S_ l } -_e_--T(x, aT (c,l) I)+-I { dt __ t))dlVdc 0 CoSlV 2 v al

+ f 10(l-R)o 2A2

J ff ?{eC-1 x-c I A COSlV)~} 1

-00

cos 2 lV

0

With the evaporation term ' pLCT,)Vs' added at 'x

~

0'

I

j e(-oP)dp c

I

dlVdc

(22)

14

~r::: }= (I - f)

I~

_004,13

7T ?{e(-I X-6 I IAcosw) sin w} x {{T,,(6,t) 0 cosw

+/

I ~7Tf2{e(-IX-61IACOSW) 3

-00

4.-i

+~{dt _~} aTe (6,t)}dWd6 2

at

v

sinw} T(6,t)dwd6 cos W

0

9K a + / 10 (I -2R )5 wJ 7T J/2{e(- I X- 6 I IA cos w) sin2 w } I X_I ",,( -5p)dp I dwd6--T (x,t)+V_ -[pC T]

_ 00 0

2,1

cos

W

2,12

6

e

s

ox

p

(23)

aK

00

at

-00

J 7T J12{ _V K __ e(-Ix- 6 1/ .-icosw) 0

2,12

•

SInW } dwd6- Kv A cosw

(24)

This gives a system of nonlinear integro-differential equations, which are solved using numerical methods_ Results Figures (6) and (7) show the variation of electron and lattice surface temperature with time, these figures also show the laser input pulse that was used to produce the simulation_ It can be seen that the electron temperature distribution closely follows the temporal profile of the laser input pulse, with a small time lag_ Once evaporation is significant the lattice surface temperature stays reasonably constant, due to the material evaporation; the difference in temperature between the lattice and the electrons becomes quite large_

2.6

Electron

Electron

2_1 ~

~ ~

~

= ~

£

1.95

IA

L3

0_7

Lattice

0.65

Time ps

2.75

3.25

3.75

4.25

4.75

Time IlS

2.75

Time J-ls

Figure (6) Surface Temperature Variation in Aluminium using the Kinetic Theol)'

3.25

3.75

4.25

4.75 Time J1S

Figure (7) Surface Temperature Variation in Copper using the Kinetic Theory

Figure (8) demonstrates the dramatic effect that non-equilibrium energy transport conditions have on the spatial distribution of the energy within the lattice_ Fourier theory suggests that the energy is distributed deep into the body of the material, whereas kinetic theory predicts that the energy will be concentrated near the surface, which agrees with the experimental observations of pulsed laser radiation interacting with a metal target

15 1.0 0.8

0.9 0.8

0.6

~

0.'

f

0.0

6= 0.84 x 108 mol .\=0.149 x IO·7 m

0.5

J) Kinetic theory 2) Fourier theory

~

,: ~

~

t=2.5I.1 s

~

0.4

Electron

~

E

t!

0

~

t.t = 0.6 ~s is= 0.75 X 10' m" A=0.4 x 10"m

"Il::s &."

0.4 0.3

6.

7.0

0.6

0.4

0.2

0.2~~~~

0.1 0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.0 .t:;::: 0.0 1.0

3.5

2.

3.0

4.0

5.0

6.0

7.0

o Oepth in microns

Depth in Microns

Figure (8) Lattice Temperature Profile in Aluminium

Figure (9) Temoerature Profile in Cooner Usine the Kinetic Theorv

Figure (9) illustrates the spatial evolution of the temperature within the material. In the surface region there is a large positive temperature gradient that becomes established in the lattice due to evaporation; on the scale at which the graph is plotted it is not possible to see this as the positive temperature gradient only extends to a depth of a few mean free paths. Evaporation does not greatly affect the electron temperature distribution. The kinetic theory predicts that the lattice temperature increases with depth into the material which leads us to the conclusion that it is possible for subsurface explosions to occur and indeed this is observed to be the case in experimental studies. Figure (9) also illustrates the temperature difference between the lattice and the electrons. 1) 2)

0.' 3)

Experimental Electron - Kinetic theory Lattice -Kinetic

theory 4)

0.4 5)

e ~

8. 0.3

/

~

/ I

~ 0.2

0.'

.,

:'

l'

/ /

3

I

.Ii

"C

u

5

/

I,

a:a:

/./ ~ /t /. ,

..;

/

i.'

~

"

5)

h

/i .:,

E

/i'

a:

4)

2j I, II

~

/~.

ii=

/7

e ~

3

Experimental Electron - Kinetic theory Lattice - Kinetic theory Electron I LatticeFourier theory / Laser Power

2) 3)

Electron I Lattice Fourier theory Laser Power

I,.

>-

1)

/

/ /

i:

J ~

B

4

0.0 +'o----:or.,----:,r.o---<,."",----:2.>-0----:2>-.,---<,.""0----:,.r,--+,.0 Time 1-15

Figure (10) Surface Temperature Evolution for Aluminium

o

0.5

1.0

1.5

2.0

Time IJs

Figure (II) Surface Temperature Evolution for Nickel

Figures (10), (II) and (12) give a comparison of predicted surface temperature, for aluminium, nickel and copper, using the Kinetic and Fourier theory for a laser pulse from an Nd 3 , :Glass laser operating at a wavelength of 1.06[.lm. Using a two-colour temperature measurement technique we measured the surface temperature, this surface temperature measurement is actually a measurement of the electron temperature, which for slower heating processes would be in equilibrium with the lattice phonons. When considering all the complex interactions that are actually taking place our model is very crude but nevertheless in the initial heating phase it gives a good prediction of the

16

electron temperature. The model results are quite good for nickel even at high temperature. Clearly Fourier conduction theory is wildly inaccurate for these rapid heating rates. 1) 2)

Experimental Electron Kinetic theory Lattice Kinetic theory Electron I

3)

4)

Lattice Fourier."" theory

...-

laser Power:""

s) 0.'

(" (

0.4

.t"

/./

~

'" . '

3,' / 2.. '

~

I-

~

5

0.3

Co

.""

0.2

///

~

~

//

··

0.

al

'"

0.1

..J

..... 0.0 >-'-/-+--e--+----<--+----+o 0,5 1.0 1.5 2.0 2.5 3.0

-+-_ 3.5

4.0

Time f.ls

Figure (12) Surface Temperature Evolution for Copper

Conclusions The validity of the Kinetic theory for modelling the heating interaction has been justified by the experimental results that give good agreement in the initial heating phase and for some materials still give good results at high temperatures. This simple model helps us to understand why we get explosive heating interactions with fast laser pulses and also assists us in understanding why we get such a small heat affected zone with laser materials processing. The model provides a greater understanding of why the surface plasma evolves very rapidly due to the concentration of laser energy in the surface regions of the material being processed. References C,Kittel, Introduction to Solid State Physics, John Wiley and Sons, Inc. 1971. 1.M.Ziman, Electrons and Phonons, Clarendon Press, Oxford 1960. 3 A.M.Cravath, The Rate at which Ions Lose Energy in Elastic Collisions, Phys. Rev., Vol. 36, p 248, 1930. 4 M.von Allmen, Laser drilling velocity in metals, J.Appl. Phys., Vol. 47, No. 12, P 5460-63, 1976. 5 L.D.Landau and E.M.Lifshitz, Staistical Physics, Pergamon Press, New York, 1959. 6 A.M.Prokhorov,V.A.Batanov, F.V.Bunkin, V.B.Federov, Metal evaporation under powerful optical radiation, 1.Quant. Elect.,Vol. QE-9, No.5, P 503, 1973. 7 J.Frenkel, Kinetic theory of liquids, Clarenden Press, Oxford, 1946. I

2

1-2. Invited Lectures

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LASER ACCELERATORS Lotfia M. El Nadi*l, Mohy S. Mansour, Galila Abdellatif l and Mohamad Atef Reda 2

1 Physics Dept., Faculty of Science and IC-SAS, NILES, Cairo University, Giza, 12613, Egypt 2 National Institute of Laser Enhanced Sciences and IC-SAS, NILES, Cairo University, Giza, 12613, Egypt *lotfianadi@ gmail. com

Abstract It is now a fact that focusing an intense ultra short laser pulse onto a gas jet or thin targets, generates energetic collimated electrons or ions forming ultra short beams of energies > 100 MeV. The different mechanisms to explain such laser accelerated electrons or ions will be discussed. Data obtained by recent experiments will be presented. We report the experiment planed to study laser accelerated ions and/or particles using picosecond and femtosecond high energy laser pulses focused to achieve intensities> 10 18 watts/cm 2 . The design of the interaction chamber and the choice of targets as well as the ultra fast detection techniques will be speculated. This source of accelerated ions having unique properties is expected to become an interesting tool for many fields in physics, chemistry and biology. It can enable advances of devices to be used in medicine. Key Words: intense Short Pulse Lasers, Electron acceleration, Ion Acceleration, design of experiment, detection techniques, Applications.

1 Introduction Interaction of laser beams with matter attracted several hundreds of researchers since the invention of lasers in 1960. Laser pulses of ms, IlS and ns duration were utilized to interact with solid, liquid or gas targets of metals, compounds or biological materials. Revolutionary results and thousands of publications enriched knowledge in this field and laid down applications in industry and medicine. As the laser power reached MW with ns pulse duration based on Q-switch techniques, it became possible to produce plasmas with ion energies in the Ke V range (I). Self-similar plasma expansion models (2) could explain such undirected ion emission. The ultra fast lasers based on the genius ideas of Strickland and Mourou. Chirped Pulse Amplification CPA technique (3), paved the way to the field of relativistic laser-plasma physic. This fast growing field points to an important breakthrough phenomena of electron acceleration to velocities close to the velocity of light (4-7). In addition highly direct ion beams with small transverse emittance (8-10), marked the differences from ion beams emitted from nanosecond laser-plasmas. Such interesting findings

19

20 happens for short laser pulses with intensities IL > 10 18 W/cm 2 for wavelengths -I J..lm. Short pulses stands for laser pulse durations of femtoseconds and picoseconds time duration. Focusing such pulses provide laser intensities per pulse of 10 18 _10 24 W/cm 2 • During the last twelve years ion energies could be achieved with energies up to 100 MeV/u. These accelerated ions particularly MeV protons (11) were emitted with intensities up to 1010_10\3 particles per pulse .There are promising applications of such accelerated protons in Ion Beam Cancer Therapy mCT (12), in producing short lived positron emitting isotopes to be used in nuclear medicine (13), in imaging of electromagnetic fields in over dense plasma and in their use in fast ignition and inertial confinement in fusion processes (14).We already have available two high intensity short pulse lasers. The first one is 2 J, 120 picoseconds laser that could be upgraded to 10 J, 2 picoseconds laser. The second one is a 150 mJ, 50 femtosecond Ti: Sapphire laser which is still under development at NRC. The focused power for the first laser could reach an order of 10 18 W/cm 2 and that of the second 1020 W/cm 2 • Shortly a 30 TW Ti: Sapphire laser project will be developed at Cairo University. Therefore we find it important to study the processes involved in Ultra Fast Laser Plasma Interactions UFLPI. Here we shall report the expected processes involved, describe the laser facilities to be utilized, design the experimental set up and the equipments needed to achieve precise diagnoses of the intensities and distribution of the initiated electrons and/or ions under specific conditions.

2 Concept of Laser Plasma Interaction The electric field Eo measured in Vim in plasma of frequency to be generated in the wake field of the laser pulse.

(J)p

is well known

Energy would be

(1)

Since

(2)

Substituting the values of c, ll1e, e and Eo Eo = 96 neY'V/m

(3)

For plasma density ne = 3.9 x 10 18 cm· 3 Eo = 190 GV/m

(4)

21

much less than the critical density nc defined as nc = l.1 x 1021 / AL(Jlm) cm- 3 . When AL the wavelength of the propagating laser beam in the plasma is in Jlm = 1 nc = 1.1 x 10 21 cm -3 ne « nc to achieve the conditions of transparent plasma to allow laser propagation. Today, a standard linear accelerator that could accelerate ions to MeY/A energies in RF accelerators, the electrostatic field is less than 100 MY/m. The above value for the laser pulse propagating through the plasma simulates a yacht gliding in a river forming traveling wake waves . Energy would be efficiently transferred between the wave and the particles in the plasma if both move with the same speed. This is known as laser wake field acceleration regime LWFA.

2.1 Laser-Electron Acceleration Long-pulse high intensity laser interaction, would lead to electron gain of transverse momentum providing undesirable growth of electron acceleration. Acceleration of electrons could be possible through different mechanisms:

PBWA Laser Beat Wave Acceleration regime SMLWF Self Modulated Laser Wake Field regime Forced Laser Wake Field regime FLWF

•

Laser Wake Field Accelerator(LWFA) A single short-pulse of photons

•

Plasma Beat Wave Accelerator(PBWA) Two-frequencies, i.e., a train of pulses

•

-.N

+

Self Modulated LaserWake Field Accelerator(SMLWFA) Raman forward scattering instabil

evolves to--.t~II.IIfIT

Fig. I. A schematic representation of the different mechanisms involved in electron acceleration when a High intensities Laser propagates through a plasma for smgle frequency or two flequencles short pulse lasers.

22 The First Mechanism stands for plasma wave driven by two laser pulses of two different AL (not short). The Second Mechanism represents laser pulse length more than the plasma wavelength where CT > t". In this case the laser pulse envelope is modulated at t" and resonantly drive amplification of the plasma wave. The transmitted laser beam exhibits Forward Raman Scattered (FRS) satellites with frequency (wo ± nw p) wo, where the laser frequency is wo, plasma frequency is wp and n is an integer representing satellite order. These mechanisms are schematically represented in Fig. 1. The Third Regime corresponds to the fact that the laser pulse is compressed by the group velocity dispersion. The plasma amplitude a = () nel ne can resonantly be excited by the ponder motive force of the laser pulse. The laser pulse duration T in this case is half the plasma wave period Tp =2n Iwp . The local vibration in the group velocity v = c (1- w p2/w o2 ) 112. The FLWF can produce much larger accelerating fields than SMLWF regime (15). Recently it has been reported that electron acceleration is transferred into the bubble regime, where the accelerated electrons become mono-energetic (16). Electrons can also be boosted to high energies over very short distances by surfing on the formed surface of the electrostatic wave (17).

2.2 Laser Ion Acceleration In particular proton pulses confined in time and space were noticed and measured (18) when high intensity short pulse lasers interacted with thin foils. The pulses contain ion numbers exceeding 1010 particles with MeV energies. Theoretical models simulating such phenomena like Particle In Cell (PIC) and Plasma Expansion Model (PEM) (19,20) could explain the physical features of the process. Wilkes et at gave (21) a deeper view of the processes. The laser relativistic pulse formed by the CPA process, favors the formation of a pre-pulse which is intense enough (> 10 12 WI cm 2) to ionize a thin foil target to form a pre-plasma. The following main laser pulse interacts with the pre-plasma at the target front side. The laser can propagate in the pre-plasma of density below the critical density till it reaches the surface of the critical density where it will then be reflected. The plasma electrons are accelerated in the forward direction, pass through the thin target foil and set up a strong electrostatic field that exceeds 1 TVI m. This field ionizes the rear surface of the foil and accelerates the ions to energies of several MeV.

23 relativistic

1OJ, 100fa laaer pulse

electron cloud

proton beam

Fig. 2. Schematic representation of the process known as Target Normal Sheath Acceleration with estimation of Ion energy distribution (P. K. atel et ai, Proton acceleration data from LLNL presentation 5/2412004).

Such process is known as TNSA Target Normal Sheath Acceleration has been elaborated as an analytical model by B. M. Hegelich et al (22) from which estimation of the maximum ion energy could be obtained when certain properties of the laser pulse and target thickness were applied.

3 Experimental Set-Up The main components of the experimental set-up to study the generation of laser accelerated particles, electrons, protons or ions are: a high density short pulse laser system, a target chamber and diagnostic system suitable to each type of accelerated particles.

3.1 The high Density Picosecond Pulse Laser As shown in figure 3 it consists of a picosecond silicate glass laser (Continuum) utilizing a CW mode-locked Nd:YAG oscillator producing l20ps pulse duration of energy 1III operating at 100 MHz. The pulses from the oscillator are fed to a regenerative amplifier emitting pulses at 10 Hz of energy 50 mJ. Utilizing double path configuration the energy reached 400 ml and amplified through two

24

Nd silicate glass rods of cp 45rnm and 64 rnm laser amplifiers. The output beam has a smooth hole free (in the far field) intensity profile and divergence < 500 microrad after passing through a 50 cm spacial filter. The output beam diameter is 25 mm with output energy 2J and pulse duration 120 ps at a repetition rate of 6 pulses per minute. A deformable mirror at the beam output and off axis parabolic gold mirror inside the target chamber could be used to focus the beam on the target down to an area of 10 f.lm 2 .

Fi g. 3. The picosecond silicate glass laser with output laser beam of energy 21 and pulse duration 120 ps at reprate 6 pulses per minute. The Oscillator appears at the front and the amplifying stages at the annular white cubes. The output beam wavelength is 1054 nm that could be SH doubled to 527nm and 3'd H to 351.3 nm using 3" KDP crystals.

3.2 The Femtosecond High Power Laser The CPA Ti: Sapphire laser shown in fig. 4 is still in progress and will be istalled by 2008 at NRC. The oscillator is a frequency-doubled Nd:YV0 4 (Coherent, Micra). The pulses from the oscillator are stretched by an offner-type stretcher and are selected by a Pockels cell. The selected pulse is then to be

25

amplified by a preamplifier pumped by a Q-switched frequency doubled Nd:YAG laser operating at 10 Hz. A main amplification system 4 pass Ti: Sapphire pumped by another Q-switched Nd:YAG laser and a pulse compressor that could boost the energy to 150 mJ and generate 50 fs pulses with peak power of nearly 3 TW in a beam size of IP equals 4.5 cm and repetition rate 10Hz.

Fig. 4. Schematic The CPA Ti: Sapphire laser consist of from the top left appears the oscillator next to the stretcher and pulse selector ,then to the preamplifier pumped by the Q-switched Nd:YAG. From the preamplifier to the mUltipass amplifier then boosted in the compressor to provide the output beam at the bottom left. Each unit could be remotely supervised to adjust the properties of the output beam.

3.3 The Target Chamber The target Chamber fabricated in local workshops is shown in fig. 5. It is a stainless steel cylinder of IP 70 cm and length 70 cm with its axis laying in the horizontal plane. The front flange connector has only one input central 3" flange with a quartz window to allow the beam entrance into the chamber. The rear flange has three 6" flanges. One to be used for remotely control the diagnostic rd systems, the second is to illuminate and view the chamber internally. The 3 is to connect the turbo pumping via bellow to isolate the target chamber from mechanical vibrations during evacuation. The chamber is provided by an optical table in order to easily and accurately set up the target and the diagnostic equipments.

26

Fig. 5. The open target chamber showing the optical table with the optical tools.

3.4 Diagnostic Equipments In this type of experiments it is necessary to use equipments to control and identify the laser beam properties outside and inside the target chamber as well as equipments to characterize the generated particles from the laser taget interaction processes.

3.4.1 Beam Diagnostic Systems For the laser beam diagnostics, a laser beam profiler is used with a CCD camera to measure directly the intensity distribution at low intensity on the target utilizing telescope optics. The partial beam energy is measured outside the chamber utilizing a suitable beam splitter. A He-Ne laser could be used easily for the pre-alignment of the incident laser beam. In all practical cases, energy of the picoseconds laser beam can be measured by sending the beam directly into the head of Scientech model 362 calorimeter or equivalent systems. In order to measure energies in the SH, one has to separate it from the infrared with two dichroic mirrors. The temporal distribution of the pulse train can be monitored by using a fast photodiode. Pulse to pulse stability can be checked by sending the output of the photodiode to a storage oscilloscope set to the lowest sweep rate. Each laser

27

pulse displayed as a peak on the screen, whose height is proportional to the pulse energy.

3.4.2 Plasma Plum Imaging A gated OMA system integrated to al2 bit CCD camera could be used to image the laser produced plasma at low vacuum conditions. One can re-image the scattered light 'both perpendicular and parallel to the laser direction.

3.4.3 Accelerated Electron Diagnosis The electron divergence produced as explained earlier, could be measured by a removable LANEX scintillating screen monitored by a CCD camera within 3_60 opening angle. The energy spectrum of the electrons up to I 00 MeV could be measured by placing a suitable magnet before the LANEX screen and recording the trajectories as a function of the applied magnetic field . This forms the electron spectrometer. A Time Of Flight (TOF) system could also be applied.

3.4.4 Accelerated Proton Measurements The accelerated protons or ions from the target rear surface in the laser propagation direction x-axis, could be detected by a stack of Radio chromic Films (RCF) and/or Thomson parabola (TP) spectrometer using CR-39 track detectors. This spectrometer is simply formed of a magnet with two pinhole entrance collimators for the accelerated positive ions entering axially the magnetic field chamber. On the other side of the magnet the ions leaving the magnetic field could impinge on the CR-39 Screen placed in the y-z plane at known distance from the exit end. Knowing the magnet gap geometry, the magnetic field and the electric field and the position of the track detector, could easily help to calculate the expected trajectories of the different accelerated charged particles.

4 Planning Analysis of the Experimental Results Experimental set-ups are planned to generate simultaneously accelerated electrons and positive charged particles and demonstrate the laser acceleration

28 phenomena using focused terawatt powers from the picoseconds and femtosecond lasers. By the end of 2008, we plan to use a virtual gas jet target for experiments with the ps laser to generate accelerated electrons. A rolling type target of thin films of Al and/or polyethylene thin sheet targets of thickness 1-3 flm are used for proton generation applying the fs lasers. Electron microscope mesh grids covered with 1-2 mm carbon layer are targets to be used for the production of accelerated carbon ions of different ionization stages under the TW fs laser interaction,wiII be performed at NRC in the spring 2010. Calculations using the theoretical model based on particle in-cell simulation (PIC) ( ) and plasma expansion (PEM) are being carried ( ) out to investigate the dependence of the ion spectra on the intensity and target thickness. The calculations are to be published elsewhere applying the process TNSA.

5 Conclusion At Cairo University we are having an ambitious view to study the interaction of high density laser short pulses with plasmas in an attempt to understand the highly nonlinear physical processes involved in such complicated mechanisms. We exposed in this paper the efforts to complete the experimental set-ups to perform the experimental measurements and demonstrate the importance of the field of Laser Particle Acceleration. The numerous fields of application in medicine, industry and new energy resources are already booming in the big projects around the world. We would like to acknowledge the support of the Industry Innovation Authority.

References [1]

[2] [3] [4]

SJ. Gitomer, R.D. Jones, F. Bergay, A.W. Ehler, J.F. Kephart, R. Kristal, Fast ions and hot electrons in the laser Interaction, Phys. Fluids 29, 2679 (1986) W.L. Kruer, The physics of laser plasma interactions, Addison-Wesley Publishing Company, New York (1988) D. Strickland, G. Mourou, Compression of amplified chirped optical pulses, Opt. Comm. 56, 219 (1985) T. Katsouleas, Accelerator physics: Electrons hang ten on laser wake, Nature 431,515 (2004)

29 [5]

[6] [7] [8] [9] [10] [11]

[12]

[13] [14] [15] [16] [17] [18] [19] [20] [21]

[22]

1. Faure, et ai, A laser-plasma accelerator producing monoenergetic

electron beams, Nature 431, 541 (2004) S. Mangles, et ai, Monoenergetic beams of relativistic electrons from intense laser-plasma interaction, Nature 431,535 (2004) c. Geddes, et ai, High-quality electron beams from a laser Wakefield accelerator using plasma-channel guiding, Nature 431,538 (2004) F.N. Beg, et ai, A Study of picosecond laser-solid interaction up to 10 19 W/cm 2 , Phys. Plasma 4, 447 (1997) R.A. Snavely, et ai, Intense high-energy proton beams from petawatt-laser irradiation of solids, Phys. Rev. Lett. 85, 2945 (2000) A. Maksimchuk, et ai, Forward ion acceleration in thin film driven by a high-intensity laser, Phys. Rev. Lett. 84, 4108 (2000) E.L. Clark et ai, Energetic heavy-ion & proton generation from ultraintense laser-plasma interactions with solids, Phys. Rev. Lett. 85, 1654 (2000) 1.A., Cobble, et ai, High resolution laser-driven proton radiography, J. AppJ. Phys. 92, 1775 (2002) K. Ledingham, et ai, High power laser production of short-lived isotopes for positron emission tomography, 1. Phys. D 37, 2341 (2004) R. Kodama, et ai, Fast heating of ultrahigh-density plasma as a step towards laser fusion ignition, Nature 412,798 (2001) V. MaIka, et ai, Electron Acceleration by a Wakefield forced by an intense ultra-short laser pulses, Science 298, 1596 (2002) A. Pukhov, Three dimensional simulations of ion acceleration from a foil irradiated by a short-pulse lasers, Phys. Rev, Lett. 86, 3562 (2001) Z. Najmudin, et ai, Self-modulated Wakefield and forced laser Wakefield acceleration of electrons, Plasma 10, 2071 (2003) K. Krushelnick, et ai, Energetic proton production from relativistic laser interaction with high density plasmas, Phys. Plasma 7,2055 (2000) S. Wilks, et ai, Energetic proton generation in ultra-intense laser-solid interaction, Phys. Plasma 8, 542 (2001) A. Pukhov, et ai, Two-dimensional particle in a cell (PIC) Simulation, AppJ. Phys. B 74, 355 (2002) Nasr Hafz, et ai, Near - GeV electron beam from a laser Wakefield accelerator in the bubble regime, Nuc. Instr. & Methods, Phys. Research A 554, 49 (2006) B. M. Hegelich, et ai, laser acceleration of quasi-monoenergetic MeV ion beams, Nature 439, 441 (2006)

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1-3. Contributed Papers

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ENERGY LEVELS, OSCILLATOR STRENGTHS, LIFETIMES, AND GAIN DISTRIBUTIONS OF S VII, Cl VIII, AND Ar IX WESSAMELDIN. S. ABDELAZIZ, National Institute of Laser Enhanced Sciences, Cairo University, Egypt TH. M. El-SHERBINI Laboratory of Lasers and New Matrials, physics Department, Faculty of Science, Cairo University, Egypt Energy levels, oscillator strengths, and transition probabilities for the

I S2 2S2 2p6, 2p 531

(I = 0,1,2), 2p 541 (I = 0,1,2,3) states in S VII, CI VIII, and Ar IX are calculated using COWAN

code. The Correlation and relati vistic effects are considered. The calculations are compared with other results in the literature. A good agreements are found. The calculations are used in the determination of reduced populations for 14 fine structure levels of S VII, CI VIII, and Ar IX ions over a wide range of electron density (from 10+ 16 to 10+24 em" ) at various electron plasma temperatures. The gain coefficients are determined and plotted against the electron densities.

1. Introduction

Almost coincident with the first observations of laser action in the IR and visible spectral regions in the 1960s, the search started for lasers operating at much shorter wavelengths. Measurements of definitive high output lasing at wavelength shorter than the ultra-violet was elusive, until the mid 1980s when conclusive evidence for "X-ray laser" operating at 209 A was produced from neon-like selenium [1]. In recent years, due to their peculiar structure of closed shells, Ne-Iike ions have been widely applied in the laboratory and in astronomical plasmas. The laboratory application is shown by the successful X-ray laser in the energy level of 2p5 3p - 2p5 3s of Ne-like ions based on the mechanism of collisional excitation of electrons [2] . Since the I 990s, much progress in experimental techniques has been achieved, but experimental data of atomic parameters are still limited, and theoretical calculations carried out. Laser produced plasmas are now well known as suitable lasant media for amplification of soft X-ray energy range of the electromagnetic spectrum. There are several schemes proposed and examined in producing laser plasma condition for X-ray lasing efficiently at shorter wavelengths. Plasma based recombination lasers [3] collisionally pumped [2,3] are examples of such schemes. The dynamics of laser-produced plasma parameters such as the electron and ion temperatures and the density can be modeled by fluid hydrodynamic codes. Some examples of hydrodynamic codes include MEDUSA [4], and LASNEX

33

34

[5]. Plasma transient collision ally pumped, using picosecond Chirped pulse amplification (CPA), X-ray lasers [6], using a capillary discharge [7], a free electron laser [8], optical field ionization of a gas cell [9] are also examples of such schemes. Among various pumping techniques for the X-ray lasers the collisional pumping of different materials in the Ne-like ionization state between the 3p-3s energy levels have shown a more stable and higher output. The purpose of this work is to present the results of our calculations of energy levels, oscillator strengths, and transition probabilities of S VII, Cl VIII, and Ar IX ions, and to compare the results with other literature data. The atomic data obtained are used together with the evaluated reduced population of excited levels, to calculate gain coefficients for laser transitions in these neon-like ions under study.

2. Computation of atomic structures

2.1. Model of Central Force Field In quantum mechanics, various physical processes can be summed up by Schrodinger equation, i.e. (I)

In the non-relativistic case (the influence of relativistic effect will be discussed later), the Hamiltonian of an atomic system with N electrons is:

Z

112

H =H . +H kin

e -nuc

+H

e -e

=

2

2

"_v2 _,,_e_+ ,,~. ~ 2 ~ ~ i

I

me

i

ri

i>j

(2)

rij

Here Hkim Hem/( and Hee refer, respectively, to the kinetic energy of electrons, the Coulomb potential and the energy of electrostatic interaction of electrons, ri is the distance between the i-th electron and nucleus, and ri,j ::: I ri - rj I. By substituting the Hamiltonian into Schrodinger equation and solving the equation in the case of multiple electrons and multiple energy levels, the wave function is obtained. Now, due to the appearance of the term of interaction of electrons, an exact solution cannot be obtained. On the other hand, the interaction term is comparable with the Coulomb potential term, so it can by no means be ignored. An approximate solution is to adopt the method of central force field. If it is assumed that every electron moves in the central force field of the nucleus and also in the mean force field produced by other electrons, then we have the following effective Hamiltonian:

=I N

H

eff

i

H ieff

N

1 p2

i=l

2 me

Z

= -I {__ i +_e__ v / ff (ri )} ri

2

(3)

35

2.2. Method of calculation The key problem in the application of central field is to find an adequate potential function yeff. For this, in recent decades many effective method of calculation have been developed. Among them the more important ones are the potential model, Hartree-Fock theory, semi-empirical methods. In the following we present a brief introduction of the semi-empirical methods. Semi-empirical methods try to calculate atomic structures via solving the simplified form of the Hartree-Fock equation. The most typical is the HartreeFock-Slater method. Afterwards, Cowan et al. revised this method and developed the RCNIRCG program used in our work [10]. The merit of the program is its extreme effectiveness, and the shortcoming is its inability to estimate the precision.

2.3. Configuration Interaction In the above-stated model of central force field, every electron can be described with a simple wave function. The overalI wave function of atoms may be expressed with the folIo wing Slater determinant: =_1 [((JI(:XI)

cp

JNi.. . ((IN

(XI)

((JI(~N)] ..

(4)

((IN (XN )

In reality, such a description is not very precise. The best wave function should be a linear combination of wave functions with single configurations, and these wave functions possess the same total angular momentum and spin symmetry. This method is called the interaction of configurations. In the computation of atomic structures, consideration of the configuration interaction is the basis requirement for a program.

2.4. Relativistic correction In a non-relativistic system, the oscillator strengths and dipole transitions under LS-coupling can be calculated. In calculating forbidden transitions, jjcoupling must be used, and for this relativistic effects have to be taken into account. Generally speaking, the effects may be treated in two ways. One is inclusion of Breit-Pauli operator in the non-relativistic equation, and other is direct solution of the Dirac equation. For the former, a mass velocity term, the Darwin term caused by the electric moments of electrons and the spin-orbit term are added to the Hamiltonian of the model of central force field [11]. For relativistic correction, the program RCNIRCG [10] restore to the Breit-Pauli correction.

36 2.5. Weighted oscillator strengths and lifetimes The oscillator strength f(yi) is a physical quantity related to line intensity I and transition probability Wen'), W

(rr') = 2w 2~2 V(rr')1

(5)

me

With, I Cl gWen') Cl glf(n')1 = gf. By Sobelman[12] Here m is electron mass, e is electron charge, y is initial quantum state, w = (E (y)-E (y'))/h, E(y) initial state energy, g = (21 + 1) is the number of degenerate quantum state with angular momentum 1 (in the formula for initial state). Quantities with primes refer to the final state. In the above equation, the weighted oscillator strength, gf, is given by Cowan [10]: 8 22 (6) gf = 1l" mcaoCF S 3h

'

Where g is the statistical weight of lower level, f is the absorption oscillator strength, () = (E (y)-E (i))lhc, h is planck's constant, c is light velocity, and ao is Bohr radius, and the electric dipole line strength is defined by:

s=I(AJll p1 IlY'J')1

2

(7)

This quantity is a measure of the total strength of the spectral line, including all possible transition between m, m' for different lz eigenstates. The tensor operator pi (first order) in the reduced matrix element is the classical dipole moment for the atom in units of eao. To obtain gf, we need to calculate S first, (or its square root):

s~~=(AJllplIlY'J').

(8)

In a multi configuration calculation we have to expand the wavefunction

Iy./)

in terms of single configuration wa vefunctions, lower levels:

IPl) For both upper and

lyJ)= L Y;, IpJ)·

(9) f3 Therefore, we can have the multi configurational expression for the square root of line strength: (10) s~~ = Y

I I Pi (P] IIplllp'] ') 13 13'

to make

yJ

The probability per unit time of an atom in specific state

37

a spontaneous transition to any state with lower energy is

P (r] ) =

L A (r] ,r \] \)

(11 )

where A (yf , y'f \) is the Einstein spontaneous emission transition probability rate, for a transition from the state. yf to the state y'f \ The sum is overall state r Il l with E(rIJ I )<E(rJ ). The Einstein probability rate is related to gf with the following relation [10]: (12)

gA

me Since the natural lifetime -r( yf) is the inverse of transition probability, then: (13) which is applicable to an isolated atom. Interaction with matter or radiation will reduce the lifetime of any state.

3. Computation of gain coefficient The possibility of laser emission from plasma ions of various members of Ne-like ions via electron collisional pumping, in the XUV and soft X-ray spectral regions is investigated at different plasma temperatures and plasma electron densities. The reduced population densities are calculated by solving the coupled rate equations [13-16]. Nj [

LA

ji

+ Ne (

i<j

Ne

L C~ L C;i ) ] = +

i<j

i>j

[LNiC~ + LNiCi~ i <j

]+

i <j

(14)

LNiAij . i <j

Where Nj is the the population of level j, A ji is the spontaneous decay rate from level j to level i, C;i is the electron collisional excitation rate coefficient, and C ~ is the electron collisional deexcitation rate coefficient, which is related to electron collisional excitation rate coefficient by [17, 18].

C~= Ci~[ b. ]exp [~Ej/KTe]

(15)

gj

Where gi and gj are the statistical weights of lower and upper level, respectively. The population ofthe/h level is obtained from the identity [14,15,19].

38

N j = [ Nj

Nr

] [

N r ] [ Nt ] N e Nt Ne

(16)

Where Nr is the total number density of all levels of the ion under consideration, and Nt is the total number density of all ionization stage. The populations calculated from Eq. (14) are normalized such that [15,14,20]. 14

N

j=]

Nr

L)-j ] = 1

(17)

Where 14 is the number of all the levels of ion under consideration. After application of electron collisional, collision in the lasant ion plasma will transfer the pumped quanta to other levels, and resulted in population inversions then produced between the upper and lower levels. Once a population inversion has ensured a positive gain through F>O [21].

F=~[Nu _NI] Nu gu Where

N

_u_ and

gu

(18)

gl

NI

- - are the reduced populations of the upper level and lower

gl

level respectively. Eq. (18) has been used to calculate the gain coefficient for Doppler broadening of the various transitions in the S VII, Cl VIII, and Ar IX ions. (19)

the gain coefficient is expressed in terms of the upper state density (Nu). This quantity depends on how the upper state is populated, as well as on the density of the initial source state. The source state is often the ground state for a particular ion. Here KT; represents the ion kinetic temperature in eV. fl == 2Z, where Z is the atomic mass number. 4. Results and Discussions

4.1. Energy levels and Oscillator strengths: Adopting the program RCNIRCG [10], we have computed the parameters of atomic structures of S VII, Cl VIII, and Ar IX respectively. The energy levels considered in the calculation have 65 fine structures ranging from ground state Is2 2S2 2p6 to 2p53l (1= 0,l,2)and 2p54l (1= 0,1,2,3) states. Our computation has yielded the energy level intervals of electric dipolar spectral transitions, oscillator strengths and transition probabilities. In our calculation of wave functions, the relativistic correction is taken into consideration.

39 The data bases, including tables of parameters, wavelengths, energy levels, weighted oscillator strengths and transition probabilities for the S VII, CI VIII and Ar IX spectrum, are available in the electronic version of this paper only [on the world wide web, at http://www.niles.edu.eglftp/Acr8173.tmp.pdf] 4.2. Gain distributions 4.2.1. Level populations

The reduced population densities are calculated by solving the coupled rate Eq. (14) using the CRMO code [22] for solving simultaneous coupled rate equations for 14 fine structure levels in every ion. Our calculations for the reduced populations as a function of electron densities are plotted in figures(1 to 9) at three different plasma temperatures (114, 112,3/4 of the ionization potential) for S VII, CI VIII, and Ar IX ions. In the calculations, we took into account spontaneous radiative decay rate and electron collisional processes between all levels under study. The behavior of level populations of the various ions can be explained as follows: in general, at low electron densities the reduced population density is proportional to the electron density, where excitation to an excited state is followed immediately by radiation decay, and collisional mixing of excited levels can be ignored. This results are in agreement with that of Feldman et.al.[15,16,23]. At high densities (N >10 2°), radiative decay to all levels will be negligible compared to collisional depopulations and all level populations become independent of electron density and are approximately equal (see figures 1 to 9). The population inversion is largest where electron collisional deexcitation rate for the upper level is comparable to radiative decay for this level [15,22].

40

1.E-01 1.E-02 c

.Q

1.E-03

_

2 4 -6 8 D 10 12

_1 --6--3 _5 --+-7 _ 9 j, 11 -13

1§

::::J 1.E-04 a. 0 a. i.E-OS -c Ql () 1.E-06 ::::J -c ~ 1.E-07 .

-~14

1.E-08 . 1.E-09 15

16

17

18

20 21 19 log Ne(cm3)

22

23

24

25

Figure I . Reduced population of S VII levels after electron collisional pumping as a function of the electron density at temperature 114 ionization potential

1.E-01 1.E-02 c

1.E-03

0

~ ::; 1.E-04 a. 0 a. i.E-OS -c

_1

Ql

()

::::J

-c ~

1.E-06 1.E-07

2 4

_5

-6

--+-7 _ 9

--8 D

10

11

..-- 12

-13

-~14

j,

1.E-08

_

--6--3

1.E-09 15

16

17

18

19

20

21

22

23

24

25

log Ne(cm3)

Figure 2. Reduced population of S VII levels after electron collisional pumping as a function of the electron density at temperature 112 ionization potential

41 1.E-01 1.E-02 c

o

1.E-03 -

~ "S 1.E-04 a.

8..

-+-1 ___ 2 -6-3 ---*- 5 ____ 64 -1-7 8 -+- 9 0 1 ---.t.- 11 ~ 1 -13--1

1.E-05

"0

g 1.E-06 .

"0

~ 1.E-07

1.E-08 1 .E-09

.l......--.1._ _-----"_ __ _- - - - ' - _ - ' - -----'-_-'-------"

15

16

17

18

19 20 21 log Ne(cm3)

22

23

24

25

Figure 3. Reduced population of S VII levels after electron collisional pumping as a function of the electron density at temperature 3/4 ionization potential

Where the labels in the above figures refer to the following fine structure levels

1- (2P1 /2 3S 1/2 )1

8- (2P1/2 4S 1/2 )1

2- (2P1/2 3P1/2 )1

9- (2P1/2 4P1/2 )1

h

3- (2P1/2 3P1/2 )0

10- (2P1/2 4P3/2

h 5- (2P1/2 3d 3/2 h 6- (2P1I2 3d s/2 h

11- (2P1/2 4P1/2 )0

7 - (2P1/2 3d 3/2 )1

14- (2P1/2 4d 3/2 )1

4- (2P1/2 3P3/2

12- (2P1/2 4d s/2 h 13- (2P1/2 4d 3/2 h

1.E·01 1.E·02 1.E-03 c: o ~ 1.E·04 "5 & 1.E-05 -+-1 -g ---ir-3 g 1.E·06 ---ilE-5 1? 1.E·07 --+-7 -+- 9 1.E·08 .. 11 1.E.09 L-_ _~~_~_ _ _~_~J.._ _..:: 13=___ 15 16 17 18 19 20 21 22 23 24 25 Co

"0

____'c..:J

log N.(cm-3)

Figure 4. Reduced population of CI VIII levels after electron collisional pumping as a function of the electron density at temperature 1/4 ionization potential

42 1.E-01 c 1.E-02 0 ~ 1.E-03 "S 1.E-04 0.. 0 0.. 1.E-05 "0 Q) 1.E-06 () :::J "0 1.E-07 ~ 1.E-08 1.E-09

-+-1 --0-3

_2

~5

4 -+-6

21

23

- t - 7 ~- 8 -+- 9 0 10 - . - 11 --*- 12 -13--14

15

16

17

18

19

20

log N e {cm·

3

22

24

25

)

Figure 5. Reduced population of Cl VlII levels after electron collisional pumping as a function of electron density at temperature 112 ionization potential

1.E·01 1.E·02 1.E·03

§

'iii

1.E-04

8.

1.E·05

~

1.E-06

~

~

-+-1 --0-3 ~5

-t-7 -+- 9

1.E-0?

_2 4 -+-6 ~- 8

10 12 -13 --14 ____~_~__~=====:;:::::._ 0

~- 11

1.E-OB 1.E-09

L 15

16

1?

1B

19 20 Log N, (em" )

21

22

23

24

25

Figure 6. Reduced population of Cl VllI levels after electron collisional pumping as a function of the electron density at temperature 3/4 ionization potential

Where the labels in the above figures refer to the following fine structure levels

43

1- (2P1 /2 3S1/2 )1

8- (2P1 /2 4S 1/2 )1

2- (2P1 /2 3P1 /2 )1

9- (2P1 /2 4P1 /2 )1 10- (2P1 /2 4P3/2 h 11- (2P1 /2 4P1 /2 )0 13- (2P1 /2 4d 3/2 h

3- (2P1 /2 3P1 /2 )0 4- (2P1 /2 3P3/2 h 5- (2P1 /2 3d 3/2 h 6- (2P1 /2 3d 5/2 h

12- (2P1 /2 4d 5/2 h 14- (2P1 /2 4d 3/2 )1

7- (2P1 /2 3d 3/2 )1

1.6-01 1.6-02 . c 0

§

1.6-03 .

:::J

1.6-04

8..

1.6-05

a. "0 CD

c..>

-+-1 -ir- 3 -lIE- 5 -1- 7 -+- 9 • 11 -13

1.E-06

:::J

"0

~

1.E-07

___ 2 4 ---*- 6 --8 0 1 11' 1 - -1

1.6-08 1.6-09 15

16

17

18

19 20 21 log N. (crTJ'l)

22

23

24

25

Figure 7. Reduced population of Ar IX levels after electron collisional pumping as a function of the electron density at temperature 1/4 ionization potential

1.E·01 1.E·02 l.E·03

:, ~ 1.E-04

_ 2 -+-1 ---lr- 3 4 _._5 --'-6 -5 1.E-06 ~ - - 8 -+- 7 l.E·07 10 0 -+- 9 11 _._ 12 l.E·08 -13 -14 l.E.09L-----~~-~-========~~

i~

1.E-05

•

15

16

17

18

19

20

21

22

23

24

25

log N,(cm·'j

Figure 8. Reduced population of Ar IX leve ls after electron colli sion al pumpin g as a fun cti on of the elec tron density at temperature 112 ionization potenti al

44 1.E-01 1.E-02 ____ 2

§ 1.E-03

-+-1 -(r-3

~ "3 1.E-04 0.

8. 1.E-05

-

-/- 7 -+- 9 11 10 -13

"C Ql

g "C

~

_____ 64

~5

1.E-06 1.E-07

--8 0 10 12 --14

'*

1.E-08 1.E-09

.l...-_ _ _ _ _ _- - - ' - _ - ' - _ - - - " - - - _ - ' - - - _ L . . - - - - ' _ - - '

15

16

17

18

19

20

21

22

23

24

25

log Ne(crITJ) Figure 9. Reduced population of Ar IX levels after electron collisional pumping as a function of the electron density at temperature 3/4 ionization potential

Where the labels in the above figures refer to the following fine structure levels

1- (2P1 /2 381/2 )1

8- (2P1 /2 48 112 )1

2- (2P 1/2 3P1 /2 )1 3- (2P1 /2 3P1 /2 )0

9- (2p 1/2 4P1 /2 )1

l2 l2 6- (2P1 /2 3d 5/2 h 4- (2P1/2 3P3/2 5- (2P1 /2 3d 3/2

7- (2P1 /2 3d 3/2 )1

10- (2P1 /2 4P3/2 l2 11- (2p1 /2 4P1 /2 )0 13- (2P 1/2 4d 3/2 l2 12- (2P1 /2 4d 5/2 h 14- (2P1 /2 4d 3/2 )1

4.2. 2. Inversion factor As we mentioned before, laser emission will occur only if there are population inversion, or in other words, for positive inversion factor F>O. In order to work in the XUV and X-ray spectral regions, we have chosen transitions between any two levels producing photons with wavelengths between 30 and lOOOi\. The electron density at which the population reachs collisional equilibrium approximately equal to AlD, where A is the radiative decay rate and D is the collisional deexcitation rate [15]. The population inversion is largest where the electron collisional deexcitation rate for the upper level is comparable to the radiative decay rate for this level.

45

For increasing atomic number Z, the population inversion occur at higher electron densities, this is due to the increase in the radiative decay rate with Z and the decrease in collisional deexcitation rate coefficient with Z [23] .

4.2.3. Gain coefficient As a result of population inversion there will be positive gain in laser medium. Eq. (19) has been used to calculate gain coefficient for the Doppler broadening of various transitions in the S VII, Cl VIII, and Ar IX ions. Our results for the maximum gain coefficient in cm 1 for those transitions having a positive inversion factor F>O in the case of S VII, Cl VIII, and Ar IX ions at different temperatures are calculated and plotted against electron density in figures (10 to 18). The figures show that the population inversion occurs for several transitions in the Ne-like ions, however, the largest gain occurs for the 2ps 3p - 2ps 3s transition in the three ions. This laser transition was observed with the highest output irradiances for Nelike ions in various laboratories (see for example ref. [24 D. This short wavelength laser transitions was produced using plasmas created by optical lasers as the lasing medium. For the ions in the neon-isoelectronic sequence, the rates for electron collisional excitation from the I S2 2S2 2p6 ground state to the I S2 2S2 2ps 3p configuration are greater than the rates for excitation from the ground state to the I S2 2S2 2ps 3s state. The radiative decay of the 2ps 3p level to the ground level is forbidden, while the 3s level decays very rapidly to the ground level. For electron densities and electron temperatures that are typical of laboratory high-density plasma sources, such as laser produced plasmas, it is possible to create a quasistationary population inversion between the 2ps 3p and 2ps 3s levels. Our calculations have shown that under favorable conditions large laser gains for this transition in the XUV and soft X-ray regions of the spectrum can be achieved in the neon like S VII, Cl VIII, and Ar IX ions. The gain calculations were performed at electron temperatures equal to 114, 112 and 3/4 the ionization potentials at different electron densities. It is obvious that the gain increases with the temperature as the maximum gain increases with atomic number. Moreover, the peak of the gain curves shifts to higher electron densities with the increase of atomic number. These results are in agreement with the results of Li and Nilsen [25] from scaling laws for electron density and gain coefficients in low -Z neon like X-ray lasers and also with the results of Feldman et al [16] for the scaling of laser gain and the plasma parameters with atomic number Z in the neon isoelectronic sequence.

46

6.E+02 5.E+02

--+-1/4I.P. ____ 1/2I.P. --l:r- 3/4 I.P.

4.E+02 ~t:

3.E+02

()

C

'iii Ol

2.E+02 1.E+02 1.E-02 1.E+15

5.E+16

1.E+17

2.E+17

2.E+17

3.E+17

N. (crITl)

Figure 10. Gain coefficient of laser transition (2plI2 3p'12)' - (2plI2 3s ,n), in S (VII) against electron density at different temperatures

5.E+01 4.E+01 4.E+01 ~t: ()

3.E+01 3.E+01

C 2.E+01 'iii Ol

2.E+01 1.E+01

5.E+00 1.E-02 1.E+15

5.E+16

1.E+17

2.E+17

2.E+17

3.E+17

Figure II. Gain coefficient of laser transition (2p'l2 3p'l2)o - (2p'l2 35,12), in S (VII) against electron density at different temperatures

47 1.E+03

-+-1/4I.P.

1.E+03

___ 1/21.P.

1.E+03

-to u

----{r--

8.E+02

314 I. P.

.~ 6.E+02 OJ

4.E+02 2.E+02 1.E-02

Lm~~t±~~=~=:!---.,---~----,

1.E+15

5.E+16

1.E+17

2.E+17

2.E+17

3.E+17

Ne(crrfJ) Figure 12. Gain coefficien t of laser transition (2p1l2 3pJ12h - (2p1l2 3s'12)' in S (VII) against electron density at different temperatures

8.E+03 7.E+03 6.E+03 ;:--5.E+03

to

.2. 4. E+03 c

·~3.E+03 2.E+03

-+-1/4 loP. ___ 1/2 loP.

1.E+03

----{r--

3/4 I. P.

1.E-02 dM~d::±~.------.-------,------_ 1.E+15

2.E+17

4.E+17

8.E+17

1.E+18

1.E+18

Figure 13. Gain coefficient of laser transition (2p1l2 3p '12) ' - (2plI2 3s'12) ' in CI (VIII) against electron density at different temperatures

48

9.E+02 B.E+02 7.E+02 6.E+02 ~

E 5.E+02 () C 4.E+02

'co

Cl

-+-1/4I.P.

3.E+02

1/21.P.

2.E+02

---ft- 3/4 I. P.

1.E+02 1.E-02 . 1.E+15

2.E+17

4.E+17

6.E+17

B.E+17

1.E+1B

1.E+1

Figure 14. Gain coefficient of laser transition (2pJn 3p ln)o - (2PI123sll2)1 in CI (VIII) against electron density at different temperatures

3.E+04 2.E+04

~2 . E+04 ()

-+-1/4I.P. 1/21.P. ---ft- 3/4 I.P.

C

·~1.E+04

5.E+03 1. E-02 mn~;:""~==*=~L,----~--~-r------'---1.E+15

1.E+1B

1.E+1B

Figure 15. Gain coefficient of laser transition (2pll2 3pl12h - (2p1/2 3s1/2)1 in CI (VIII) against electron density at different temperatures

49

1.E+03 1.E+03 ",1.E+03

~B.E+02 ~6 . E+02 "'4.E+02

1.E+ 15

l.E+1?

2.E+ 1?

3.E+ 1?

5.E+ 1?

6.E+1?

?E+1?

B.E+1?

Figure 16. Gain coefficient of laser transition (2p 1/2 3P ln) 1 - (2Pln 3s 112)1 in AI (IX) against electron density at different temperatures

2.E.02 2. E+D2

I .E +02 I.E ...02

":5 l.E..02 l a. E-<-o\ 6. E ~ Ol

4.E+OI

l.E +17

2.E+ 17

3.E. 17

4.E... 17

5.E+ 17

6.E t 1?

7. E. I?

8.E. 17

N.(em ])

Figure 17. Gain coefficient of laser transition (2p ll2 3pln)o - (2P II2 3S 1/2 )1 in AI (IX) against electron density at different temperatures

4.E+03 1 4.E+03 3.E+03

E

~

c:

2.E+03 .

'ro0> 2.E+03 1.E+03 - + - 1 /41.P. 5.E+02 1.E-02

1/2I.P.

_!.'fIJ~~~~~:!=~:::::~L-~~~~~~~~~.l:---l!r--~=~3/~4~1~.P~.JI

1.E+ 15

1.E+ 1?

2.E+1?

3.E+1? 4.E+ 1? N. (cm ·' )

5.E+ 1?

6.E+ 1?

7.E+ 1?

B.E+1?

Figure 18. Gain coefficient of laser transition (2P II2 3pJ12h - (2P I12 3sll2)1 in Ar (IX) against electron density at different temperatures

50

Conclusion This paper presents calculations of fine structure levels, oscillator strengths, and radiative decay rates for S VII, Cl VIII, and Ar IX ions. We shown that there is a good agreement between our results which obtained using COW AN code and the other values from NIST. The analysis that have been presented in this work shows also that electron collisional pumping (ECP) is suitable for attaining population inversion and offering the potential for laser emission in the spectral region between 50 and 1000 A from ions of the neon-isoelectronic sequence (S VII, Cl VIII, and Ar IX). This calss of lasers can be achieved under the suitable conditions of pumping power as well as electron density. If the positive gains obtained previously for some transitions in ions under study (S VII, Cl VIII, and Ar IX) together with the calculated parameters could be achieved experimentally, then successful low cost electron collisional pumping XUV and soft X-ray lasers can be developed for various applications. The results have suggested the following laser transitions in the neon-isoelctronic (S VII, Cl VIII, and Ar IX) plasma ions, as the most promising laser emission lines in the XUV and soft X-ray spectral regions(see table 10). Table 10. Parameters of the most intense laser transitions in S VII, Cl VIII, and Ar IX Elasmas: Ne (cm,3)

Ion

A(A)

a (cm'l)

S VII

1003.55

5.21E+02

1.82E+17

(2pll2 3pll2 )1-(2pI/2 3s ll2 )1 Cl VIII

833.595

7.27E+03

8.67E+17

(2p1l2 3Pl/2 )1-(2pll2 3s1/2 )1 Ar IX

727.698

1.22E+03

5.55E+17

(2pll2 3pll2 )o-(2pll2 3s ll2 )1 S VII

906.628

4. 24E+01

1.82E+ 17

(2p1l2 3pll2 )o-(2pll2 3s ll2 )1 Cl VIII

820.589

8.15E+02

6.94E+17

(2pI12 3pll2 )O-(2pI/2 3S 112 )1 ArIX

712.947

1.66E+02

4,44E+17

(2pll2 3p3/2 )z-(2pll2 3s ll2 )1 S VII

903.094

1.28E+03

1.82E+17

(2pll2 3P312 h-(2pIl2 3S 112 )1 Cl VIII

805.803

1.99E+04

6.94E+17

(2EII2 3E3/2 )r(2EII2 3s 112 )1 ArIX

697.97

3.66E+03

4,44E+17

transition (2p 112 3p 112 k(2p 112 3s 1/2

)I

51

References 1. Matthews DL, et al. Phys. Rev. Lett. 54, 110, (1985) 2. Nilsen J., J. Quanta. Spectros. Radiat. Trans. 47,171, (1992) 3. Sukewer S, et al. Phys. Rev. Lett. 55, 1753-6, (1985). 4. J. Christiansen, et aI., Comput. Phys. Commun. 7, 271 (1974). 5. G.B. Zimmermann, et aI., Comments Plasma Phys. Controlled Fusion 11,51 (1975). 6. King RE, et al. Phys. Rev. A . 64, 053810, (2001). 7. Rocca n, et al. phys. Rev. lett. 73, 2192, (1994). 8. Feldhaus J, et al. lnst. Phys. Conf. Ser. 159, 553-6, (1999). 9. Lemoff BE, et al. Phys. Rev . Lett. 74, 1574-7, (1995). 10. R. D. Cowan,"the theory of atomic structure and spectra" (Berkeley: University of California Press, 1981). II.Hartree D.R., Salpeter E.E., Quantum Mechanics of One- and Twoelectron Atoms, Berlin & New York: Springer-Verlage, (1657). 12.1. Sobelman," Atomic Spectra and radiative Transitions" (Berlin: Springer, 1979). 13. U. Feldman, A. K. Bhatia, S. Suckewer; J. Appl. Phys. 45(5),21882197,(1983). 14. U. Feldman, J. F. Seely, and G. A. Doschek; J. appl. Phys.59(12), 39533957, (1986). 15. U. Feldman, G. A. Doschek, J. F. Seely, and A. K. Bhatia; J. appl. Phys.58(8), 2909, (1985). 16. U. Feldman, J. F. Seely, and A. K. Bhatia; J. appl. Phys.56(9), 24752478, (1984). 17. G. chapline and L. Wood, Phys. Today 28, 40 (1975). 18. A. V. Vinogradov and V. N. Shlyaptsev, Sov. J. Quantum Electron. 10. 754 (1980). 19. U. Feldman, J. F. Seely, and G. A. Doschek; J.de Physique, C6-187, (1986). 20. M. J. Seaton; J.Phys. B:At.MoI.Phys. 20 P.P. 6363 (1987). 21. 1.1. Sobel'man "Introducrion to the Theory of Atomic Spectra", International Series Of Monographs In Natural Philosophy, Pergamon Press, Vol. 40, (1979). 22. S. H. Allam, CRMO computer code, private communication; (2003). 23. U. Feldman, J. F. Seely, and A. K. Bhatia; J. appl. Phys.58(11), 39543958, (1985). 24. G. J. Tallents, J. Phys. D. Appl. Phys. 36, R259 (2003). 25. Y. Li and J. Nilsen, physica scripta 57, 237 (1998).

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THE GAIN DISTRIBUTION ACCORDING TO THEORETICAL LEVEL STRUCTURE AND DECAY DYNAMICS OF W 46+ H.M. HAMED, National Institute of Laser Enhanced Sciences, Cairo University, Giza, Egypt WESSAMELDIN. S. ABDELAZIZ, National Institute of Laser Enhanced Sciences, Cairo University Giza, Egypt A. FARRAG, Laboratory of Lasers and New Materials, physics Department, Faculty of Science, Cairo University, Giza, Egypt MOHY MANSOUR, National Institute of Laser Enhanced Sciences, Cairo University, Giza, Egypt Th. M. El-SHERBINI Laboratory of Lasers and New Materials, physics Department, Faculty of Science, Cairo University, Giza, Egypt.

Level structure, oscillator strengths, and transition probabilities are evaluated for I S2 2S2 2p 6 3s 2 3p 6 3d 10 , I S2 2S2 2p 6 3s 2 3p 6 3d" 41 (1=0, I ,2,3,4), I S2 2S2 2p 6 3s 2 3ps 3d 10 41 (1=0,1,2,3,4), and I S2 2S2 2p 6 3s 1 3p6 3d lo 410=0,1,2,3,4) states inW4
1. Introduction

An important objective in the development of X-ray lasers is to deliver a coherent, saturated output at wavelengths toward the water window [i].such saturated X-ray lasers are required for holography [2] and microscopy [3] of biological specimens and for deflectometry [4], interferometry [5], and radiograohy [6] of dense plasmas relevant to inertial confinement fusion and

53

54

laboratory astrophysics [5]. Ni-like X-ray lasers, in principle, have a more favorable scaling· of laser wavelength with drive-laser energy [7,8] . Ni-like tungsten ion are of particular interest for X-ray lasing wavelength close to the range of water window. For high-Z ions, although there are a few studies on the energy levels, oscillator strengths, and transition probabilities [9-13]. Hagelstein [9] calculated the lowest 107 fine-structure levels of Ni-like Gd ion, belonging to Is2 2S2 2p6 3s2 3p6 3d 1o , Is2 2S2 2p6 3s2 3p6 3d9 41 (1=0,1,2,3,4), Is2 2S2 2p6 3s 2 3p 5 3dlO 41 (1=0,1,2,3,4), and Is2 2S2 2p6 3s 1 3p6 3d 1o 41 (1=0,1,2,3,4) configurations, and the radiative rates between the levels using YODA code. Aggarwal et al. [10] reported the energy levels and radiative rates for allowed transitions of the Ni-like Nd, Sm, Eu, Ta, and W ions using GRASP code. Zhong et al. [14] calculated the energy levels, transition probabilities, and electron impact excitations for Ni-like tantalum using FAC code. The purpose of this work is to present the energies of 107 fine structure levels, the oscillator strengths, the transition probabilities between them in W 46+ ion. The atomic data thus obtained are used to calculate reduced population of W 46+ excited levels over a wide range of electron density and at various electron temperatures. The gain coefficients are also calculated. 2. Computation of atomic structures

2.1. Model oleentral Force Field In quantum mechanics, various physical processes can be summed up by Schrodinger equation, i.e. (1)

In the non-relativistic case (the influence of relativistic effect will be discussed later), the Hamiltonian of an atomic system with N electrons is:

n

2

H =H km. +H e-nuc +H e-e

Ze 2

e2

=" - V ,~ - ,,-+ ,,-. ~ 2 f--! 1

me

2

1

~

I»

(2)

~j

Here H kim H e-nuc and H e.e refer, respectively, to the kinetic energy of electrons, the Coulomb potential and the energy of electrostatic interaction of electrons, Ti is the distance between the i-th electron and nucleus, and TiJ = I Ti - Tj I. By substituting the Hamiltonian into SchrOdinger equation and solving the equation in the case of multiple electrons and multiple energy levels, the wave function is obtained. Now, due to the appearance of the term of interaction of electrons, an exact solution cannot be obtained. On the other hand, the interaction term is comparable with the Coulomb potential term, so it can by no means be ignored. An approximate solution is to adopt the method of central force field. If it is assumed that every electron moves in the central force field of

55 the nucleus and also in the mean force field produced by other electrons, then we have the following effective Hamiltonian:

He!!

N

N

i

i=l

= LH ie!! = - L

1 p2 Z 2 {_ _ i +_e__V /!! ('i)} 2 me 'I

(3)

2.2. Method of calculation The key problem in the application of central field is to find an adequate potential function Vff. For this, in recent decades many effective method of calculation have been developed. Among them the more important ones are the potential model, Hartree-Fock theory, semi-empirical methods. In the following we present a brief introduction of the semi-empirical methods. Semi-empirical methods try to calculate atomic structures via solving the simplified form of the Hartree-Fock equation. The most typical is the HartreeFock-Slater method. Afterwards, Cowan et al. revised this method and developed the RCNIRCG program used in our work [15]. The merit of the program is its extreme effectiveness, and the shortcoming is its inability to estimate the precision.

2.3. Configuration Interaction In the above-stated model of central force field, every electron can be described with a simple wave function. The overall wave function of atoms may be expressed with the following Slater determinant: =_1 [rpl

(:XI)

cI>.JN!.

. rpN (XI)

rpl

(~N)

1

..

(4)

rpN (XN )

In reality, such a description is not very precise. The best wave function should be a linear combination of wave functions with single configurations, and these wave functions possess the same total angular momentum and spin symmetry. This method is called the interaction of configurations. In the computation of atomic structures, consideration of the configuration interaction is the basis requirement for a program.

2.4. Relativistic correction In a non-relativistic system, the oscillator strengths and dipole transitions under LS-coupling can be calculated. In calculating forbidden transitions, jjcoupling must be used, and for this relativistic effects have to be taken into account. Generally speaking, the effects may be treated in two ways. One is inclusion of Breit-Pauli operator in the non-relativistic equation, and other is direct solution of the Dirac equation. For the former, a mass velocity term, the

56

Darwin term caused by the electric moments of electrons and the spin-orbit term are added to the Hamiltonian of the model of central force field [16]. For relativistic correction, the program RCNIRCG [15] restore to the Breit-Pauli correction.

2.5. Weighted oscillator strengths and lifetimes The oscillator strength f(yy') is a physical quantity related to line intensity I and transition probability Wen'), W

2w

2 2

Or') = _e_ 3 It (yy')1

(5)

me

With, I a gWen') a glf(n')I = gf. By Sobelman[17], Here m = electron mass, e = electron charge, y = initial quantum state, w = (E (y)-E (y'»/h, E(y) initial state energy, g = (2J + 1) is the number of degenerate quantum state with angular momentum J (in the formula for initial state). Quantities with primes refer to the final state. In the above equation, the weighted oscillator strength, gf, is given by, Cowan [15]: 2 = 8:a2 meaoCT S (6)

gf

3h

'

Where g is the statistical weight of lower level, f is the absorption oscillator strength, 0" = (E (y)-E (y'»/hc, h is planck's constant, c is light velocity, and ao is Bohr radius, and the electric dipole line strength is defined by:

(7) This quantity is a measure of the total strength of the spectral line, including all possible transition between m, m· for different Jz eigenstates. The tensor operator pi (first order) in the reduced matrix element is the classical dipole moment for the atom in units of eao. To obtain gf, we need to calculate S first, (or its square root): (8)

In a multiconfiguration calculation we have to expand the wavefunction

IrJ )

In terms of single configuration wavefunctions,

for both upper and lower levels:

IPi )

57

Iy1) = Lp

Y ;,

1,81).

(9)

therefore, we can have the multiconfigurational expression for the square root of line strength:

s~~

=

IfJ IfJI

(P] II pl llpl]l)

Y /31

The probability per unit time of an atom in specific state,

(10)

y1

to make a spontaneous transition to any state with lower energy is

L A (r I ,r'I ' )

P (r I ) = where

A (yI, yl1 I)

(11)

is the Einstein spontaneous emission transition

probability rate for a transition from the state.

y1

to the state yl1 I

,

The sum is over all state ylJI with E(yl]l) <E(yJ). The Einstein probability rate is related to gf with the following relation [15]: (12)

gA

me

Since the natural lifetime T(y1) is the inverse of transition probability, then: (13)

which is applicable to an isolated atom. Interaction with matter or radiation will reduce the lifetime of any state.

3. Computation of gain coefficient The possibility of laser emission from plasma ions of various members of Ne-like ions via electron collisional pumping, in the XUV and soft X-ray spectral regions is investigated at different plasma temperatures and plasma electron densities. The reduced population densities are calculated by solving the coupled rate equations [18-21]. Nj

[L

Aji + Ne

i<j

Ne

(L Cf; + L C;i)] = i>j

i<j

~ N.C~IJ + L.J ~ N.C~IJ [ L.J I

i<j

I

i<j

]+ "" ~ i<j

N.A.. I lJ·

(14)

58 Where Nj is the the population of level j, A ji is the spontaneous decay rate from level j to level i, C;i is the electron collisional excitation rate coefficient, and C ~ is the electron collisional deexcitation rate coefficient, which is related to electron collisional excitation rate coefficient by [22-23].

Cf;= CZ[ b. ]exp [Lllij/KTe]

(15)

gj

Where gj and gj are the statistical weights of lower and upper levele, respectively. The population of the jth level is obtained from the identity[l9,20,24].

Nj

=[ N

j ] [

NI

NI ] [ Nt ] N e Nt Ne

(16)

Where NI is the total number density of all levels of the ion under consideration, and Nt is the total number density of all ionization stage. The populations calculated from Eq. (14) are normalized such that [19,20,25]. (17)

Where 14 is the number of all the levels of ion under consideration. After application of electron collisional pumping, collision in the lasant ion plasma will transfer the pumped quanta to other levels, and resulted in population inversions then produced between the upper and lower levels. Once a population inversion has ensured a positive gain through F>O [26].

F = .b.-[Nu

Nu gu Nu gu

_

N[]

(18)

g[

N

Where - - and __ I are the reduced populations of the upper level and lower

g[

level respectively. Eq. (18) has been used to calculate the gain coefficient for Doppler broadening of the various transitions in the W46 + ion. (19)

the gain coefficient is expressed in terms of the upper state density (Nu). This quantity depends on how the upper state is populated, as well as on the density of the initial source state. The source state is often the ground state for a particular ion. Here KTj represents the ion kinetic temperature in eV. ~=2Z, where Z is the atomic mass number.

59 4. Result and Discussions 4.1. Energy levels and Oscillator strengths: Adopting the program RCN/RCG [15], we have computed the parameters of atomic structures of W XXXXVIL The energy levels considered in the calculation have 107 fine structures ranging from ground state Is2 2S2 2p6 3s2 3p6 3dlO to the excited Is2 2S2 2~6 3s 2 3 f 6 3d9 410=0,1,2,3,4), Is2 2S2 2p6 3s2 3ps 3dlO 41 (1=0,1,2,3,4), and Is2 2s 2p 6 3s 3p6 3d 10 410=0,1,2,3,4) states. Our computation has yielded the energy level intervals of electric dipolar spectral transitions, oscillator strengths and transition probabilities. In our calculation of wave functions, the relativistic correction is taken into consideration. The data bases, including tables of parameters, wavelengths, energy levels, weighted oscillator strengths and transition probabilities for the W 46+ spectrum, are available in the electronic version of this paper only [on the world wide web, at http://www.niles.edu.eglftp/acr4694.tmp.pdf]

4.2. Gain distributions 4.2.1. Level populations The reduced population densities are calculated for 14 fine structure levels [(3d 3/2 4s ll2 h. (3d s/2 4pll2h, (3d 3/2 4pll2h, (3d312 4P312 h, (3d s12 4ds12h, (3d s/2 4dsd4, (3d 312 4ds12h, (3d 312 4d s12)3, (3d 3/2 4d3do, (3d 3/2 4fsl2h. (3d 3/2 4f7/2h, (3d 3/2 4f7l2h, (3d312 4f7/2)4, (3d 3/2 4fsdd are calculated by solving the coupled rate Eq.

(14) using the coupled equations eRMa code [27] for solving simultaneous coupled rate equations. Our calculations for the reduced populations as a function of electron densities are plotted in figures(1 to 3) at three different plasma temperatures (114, 112,3/4 of the ionization potential) for W 46+ ion. In the calculations we took into account spontaneous radiative decay rate and electron collisional processes between all levels under study. The behavior of level populations of the various ions can be explained as follows: in general, at low electron densities the reduced population density is proportional to the electron density, where excitation to an excited state is followed immediately by radiation decay, and collisional mixing of excited levels can be ignored. This result is in agreement with that of Feldman et.al.[20,21,28]. At high densities (N e >10 23 ), radiative decay to all levels will be negligible compared to collisional depopulations and all level populations become independent of electron density and are approximately equal (see figures 1 to 3). The population inversion is largest where electron collisional

60

deexcitation rate for the upper level is comparable to radiative decay for this level [20,28].

1.E-01 1.E-02 c 1.E-03 0 ~ 1.E-04 _ 2 --+-1 :; 1.E-05 4 ---&-3 0.. 0 ~5 -+-6 0.. 1.E-06 9 -1- 7 '0 1.E-07 (]) --+- 10 0 11 u ---&- 12 ~ 14 :::J 1.E-08 '0 - 1 3 ---&-8 ~ 1.E-09 l.E-lO 1. E-11 16 17 18 19 20 21 22 23 24 25 26

Figure!. Reduced population ofW46+ levels after electron collisional pumping a function of the electron density at temperature 114 ionization potential

1.E-01 1.E-02 c 1.E-03 0 1.E-04 ~ 1.E-05 'S 0.. 1.E-06 0 0.. '0 1.E-07 (]) u 1.E-08 :::J '0 1.E-09 ~ 1.E-10 1.E-11 16

-+-1

____ 2

---'___ 3 5

4 -+-6

- + - 7 -M- 9 - + - 10 0 11

---A-- 12 ___ 14 - 1 3 ---.- 8

17

18

19

20

21

22

23

24

25

26

log Ne (cm- 3 )

Figure 2. Reduced population of W46+ levels after electron collisional pumping as a function of the electron density at temperature 112 ionization potential

61 1.E-01 1.E-02 5 1.E-03 ~ 1.E-04 ~ 1.E-05 & 1.E-06 -g 1.E-07 !5 1.E-08 1.E-09 ·

¥

--+- 7

1.E-lO .

1.E-11

.1....._-'---_ _ _ __

16

_

~1

-+-3 ____ 5

17

18

19

_ __

20

21

2 4

---'-6 -

9

~ 10

- X

11

-+- 12 -13

_814

_

22

_

-'--_

23

~

-'---_'-------.J

24

25

26

log Ne(cm·3 ) Figure. (3) reduced population of W46+ levels after electron collisional pumping as a function of the electron density at temperture 3/4 ionization potential

where the labels in the above figures refer to the following fine structure levels

1- (3d3/24s1/2h 2- (3d s/2 4P1/2h 3- (3d 3/2 4P1/2)2 4- (3d 3/2 4P3/2 )1

8- (3d3/24ds/2h 9- (3d 3/2 4d 3do 10- (3d 3/2 4fs/2h 11- (3d 3l2 4f7/2)s

5- (3ds/24ds/2)1

12- (3d3l24f7/2h

6- (3ds/24ds/2)4 7- (3d3/24ds/2)2

13- (3d 3/2 4f7/2)4

14- (3d3l24fs/2)1

4.2.2. Inversionfactor As we mentioned before, laser emission will occur only if there is population inversion, or in other words, for positive inversion factor F>O. In order to work in the XUV and X-ray spectral regions, we have choosen transitions between any two levels producing photons with wavelengths between 30 and 1000A.The electron density at which the population reachs collisional equilibrium approximately equal to AID, where A is the radiative decay rate and D is the collisional deexcitation rate [20]. The population inversion is largest where the

62

electron collisional deexcitation rate for the upper level is comparable to the radiative decay rate for this level.

4.2.3. Gain coefficient As a result of population inversion there will be positive gain in laser medium. Eq. (19) has been used to calculate gain coefficient for the Doppler broadening of various transitions in the W46+ ion. Our results for the maximum gain coefficient in cm- l for those transitions having a positive inversion factor F>O in the case of W46 + ion at different temperatures are calculated and plotted against electron density in figures (4 to 6). The figures show that the population inversions occur for several transitions in the W 46+ ion, however, the largest gain occurs for the W46 + ion at (3d 312 4ds12 h (3d 312 4p3/2)l transition. These short wavelength laser transitions can be produced using plasmas created by optical lasers as the lasing medium. For W 46+ ion the rates for electron collisional excitation from the Is2 2S2 2p6 3s2 3p63dlO ground state to the Is2 2S2 2p6 3s 2 3p63d94d configuration are greater than the rates for excitation from the ground state to the 1S2 2S2 2p6 3s2 3p63d94p state. The radiative decay of the 3d94d level to the ground level is forbidden, while the 3d94p level decays very rapidly to the ground level. For electron densities and electron temperatures that are typical of laboratory high-density plasma sources, such as laser produced plasmas, it is possible to create a quasistationary population inversion between the 3d94d and 3d94p states in W 46+ ion. Our calculations have shown that under favorable conditions large laser gains for this transition in the XUV and soft X-ray regions of the spectrum can be achieved in the nickel like W ion. The gain calculations were performed at electron temperatures equal to 114, 112 and 3/4 of the ionization potentials at different electron densities. It is obvious that the gain increases with the temperature.

63 4.E+D2 3.E+02 3.E+02 -E u 2.E+02 C 2.E+02 'roOJ 1.E+02 5.E+01 1.E-02 1.E+15

- o - 1/4I.P. -o-1/2I.P. ---+-- 3/4 I. P.

2.E+19

4.E+19

8.E+19

1.E+20

Figure 4. Gain coefficient of laser transition (3d sf2 4dsf2 ) 1 - (3d 3f2 4P3f2 ) 1 against electron density at different temperatures 3.E+05

2.E+05

';"E

2.E+05

U

C 'ro

1.E+05

OJ

5.E+04

-o-1/2LP. ---+--3/4 LP.

1.E-02 . . . .~!Fl:b[J,,~I--,.--~-----------~-~ l.E+1S 1.E+19 2.E+19 3.E+19 4.E+19 5.E+19 6.E+19 7.E+19 B.E+19 9.E+19

Figure5. Gain coefficient of laser transition (3d 312 4d s12 h - (3d 312 4p 3/2 )1 against electron density at different temperatures

64 1.E+04

9.E+03 B. E+03 7 .E+03 . c-

6.E+03 ·

E

% S.E+D3 .~ 4.E+D3 · 3.E+03 2.E+03 1.E+03

1.E{)2 _ _IIIrlRkOi=l:1--------~--~-~--~--~ 1.E+1S

1.E+19

2.E+19

3.E+19

4.E+19

S.E+19

6.E+19

7.E+19

B.E+1 9

Figure6.Gain coefficient of laser transition (3d3/2 4d 312 )O - (3d 312 against electron density at different temperatures

9.E+19

4P3/2 ) I

Conclusion This paper presents calculations of fine structure levels, oscillator strengths, and radiative decay rates for W XXXXVII ion. We shown that there is a good agreement between our results which obtained using COW AN code and the other available experimental and theoretical values. the analysis that have been presented in this work shows that electron collisional pumping (ECP) is suitable for attaining population inversion and offering the potential for laser emission in the spectral region between 50 and 150 A from the W 46 + ion. This calss of lasers can be achieved under the suitable conditions of pumping power as well as electron density. If the Positive gain obtained previously for some transitions in ions under studies (W 46 + ion) together with the calculated parameters could be achieved experimentally, then successful low cost electron collisional pumping XUV and soft X-ray lasers can be developed for various al:plications. The results have suggested the following laser transitions in the W4 + plasma ion, as the most promising laser emission lines in the XUV and soft X-ray spectral regions. Table 4. Parameters of the most intense laser transitions in W46 + ion plasma:

Transition (3d sn4d sn )1-(3d3n4P3n) I

;\(A)

123.638

a (cm- I ) 3.03E+02

Ne (cm· 3) 6.46E+ 19

65

(3d3124d5I2h-(3d3124p3/2) I

72.291

2.31E+05

6.46E+19

(3d3124d312)O-(3d3124p3/2) I

64.104

9.32E+03

6.46E+19

Where

A: is the wavelength of laser transition in angstrom. a: is the gain coefficient in (cm· I ). Ne: is the electron density in (cm· 3). References 1. 2. 3. 4. 5. 6.

R.C Eleton, "X-RAY LASERS", Academic Press, INC. (1990). J.E. Trebes, S.B. Brown, et al. Science 238,517 (1987) . L.B. Da Silva, J.E. Trebes, et al. Science 258, 269 (1992) . D. Ress, L.B. Da Silva, et al. Science 265,514 (1994). R. Cauble, L.B. Da Silva, et al. Science 273, 1093 (1996) . D.H. Kalantar, M.H. Key, L.B. Da Silva, et al. Phys. Rev. Lett. 76,3574 (1996). 7. J.P. Christiansen, D.E.T.F. Ashby, K. V. Roberts. Comput. Phys. Commun. 7, 271 (1974) . 8. M.F. Gu, Astrophys. J. 582,1241 (2003). 9. P.L. Hagelstein, Phys. Rev. A 34, 874 (1986) 10. K. M. Aggarwal, et al., At. Data Nucl. Data Tables 74, 157 (2000) . 11. H.L. Zhang, D.H. Sampson, C.J. Fontes. At. Data Nucl. Data Tables 48, 91 (2000) . 12. U.1. Safronova, W.R. Johnson, J.R. Albriton, Phys. Rev. A 62, 052502 (2000) . 13. C.Z. Dong, S. Fritzsche, L.Y. Xie, J. Quant. Spectrosc. Radiat. Transfer 6, 447 (2003) . 14. J. Y. Zhong, et al. At. Data Nucl. Data Tables 89, 101 (2005) . 15. R. D. Cowan, "the theory of atomic structure and spectra" (Berkeley:University of California Press, 1981). 16. Hartree D.R., Salpeter E.E., Quantum Mechanics of One- and Two-electron Atoms, Berlin & New York: Springer-Verlage, (1657). 17. I. Sobelman," Atomic Spectra and radiative Transitions" (Berlin: Springer, 1979). 18. U. Feldman, A. K. Bhatia, S. Suckewer; J. Appl. Phys. 45(5),21882197,(1983). 19. U. Feldman, J. F. Seely, and G. A. Doschek; J. appl. Phys.59(12), 3953-3957,( 1986). 20. U. Feldman, G. A. Doschek, J. F. Seely, and A. K. Bhatia; 1. appl. Phys.58(8), 2909, (1985). 21. U. Feldman, J. F. Seely, and A. K. Bhatia; 1. appl. Phys.56(9), 24752478, (1984).

66 22. G. Chapline and L. Wood, Phys. Today 28,40 (1975). 23. A. V. Vinogradov and V. N. Shlyaptsev, SOy. J. Quantum Electron. 10. 754 (1980). 24. U. Feldman, J. F. Seely, and G. A. Doschek; J.de Physique, C6-187, (1986). 25. M. J. Seaton; J.Phys. B:At.MoI.Phys. 20 P.P. 6363 (1987). 26.1.1. Sobel'man "Introducrion to the Theory of Atomic Spectra", International Series Of Monographs In Natural Philosophy, Pergamon Press, Vol. 40, (1979). 27. S. H. Allam, CRMO computer code, private communication; (2003). 28. U. Feldman, J. F. Seely, and A. K. Bhatia; J. appl. Phys.58(11), 39543958, (1985).

RAMAN SPECTROSCOPY AND LOW TEMPERATURE PHOTOLUMINESCENCE ZnSexTel_x TERNARY ALLOYS A.SALAH,G.ABDELFATTAH,Y.BADR National Institute of Laser Enhanced Science (NILES), Cairo University, Egypt

I. K. ELZAWAWY Solid State Physics Department, National Research Center (NRC), Cairo, Egypt We investigated Low-Temperature Photoluminescence (PL) spectra of ZnSexTe\.x were grown from the melt where OSxSO.202, the spectra of ZnSexTel.x showing a broad band which may be attributed to self activated emission. The broad self activated (SA) emission band have been assigned to various crystalline defects, such as dislocations and vacancies or their combination with impurities, The phonon properties of ZnSexTel.x alloys grown from the melt have been studied by Raman scattering. ZnSeTe like longitudinal optical phonon modes and ZnSeTe like transverse optical phonon mode were observed in the room temperature Raman Spectra. The Raman scattering in ZnSexTel.x ternary alloys exhibit one mode behavior.

1. Introduction The mixed crystals of II-VI compound semiconductors have attracted much attention for applications to optical devices. Zinc tellurides have a direct band gap corresponding to a wavelength of the green-light region at room temperatures, and it is one of the promising materials for green light emitting devices. Graded alloys of ZnSexTe).x and digital alloys utilizing thin ZnSe and ZnTe layers are used as contact layers for Zinc selenide based optoelectronic devices in order to increase p-type doping [I, 2]. Photoluminescence spectroscopy is a contactiess, nondestructive method of probing the electronic structure of materials, Raman scattering is a useful characterization technique to study crystal structure, disorder, and phonon properties in compound semiconductors.

67

68

The phonon properties of ternary alloys have been investigated extensively by means of Raman scattering. They have been classified into three different types as follows: (1) a one-mode type behavior, i.e., their spectra show one set of longitudinal optical (LO) and transverse optical (TO) phonon modes over the entire composition range; (2) a two-mode type behavior, i.e., their spectra show two sets of LO and TO phonon modes associated with the respective constituent compounds; and (3) an intermediate- type behavior. From the point of view of lattice vibrations, phonon behavior in alloys are also interesting, Previous Raman investigations of Znl_xMgxSe [3] and Znl_xMgxTe [4] exhibited the two-mode behavior. On the other hand, results of Raman scattering in ZnSel_yTey have been studied and found to exhibit the one-mode behavior [5-8].

2. Experiment ZnSexTel_x ternary alloys were grown from the melt. The compositions of the ZnSe xTel_x were analyzed by the (Energy Dispersive X-ray Analysis) EDX micro analytic unit attached to the SEM. with (Li/Si) detector at accelerated voltage 25 KeV. Temperature dependence Raman spectra of ZnSe were carried out in the temperature range from liquid nitrogen temperature up to 358 K as well as room temperature Raman Spectra of ZnSeTe Samples in back scattering configuration by FT -Raman spectrometer. The FT-Raman spectra were measured by using BRUKER FT-Raman spectrometer of type RFS 100/S, which is attached to BRUKER-IFS 66/S spectrometer. The diode Pumped, air cooled Nd:YAG laser source with maximum laser power of 1500 mW is controlled by the software. The system is equipped with the proprietary high sensitivity liquid nitrogen cooled Ge diode. This FT-Raman attachment offers fluorescence-free Raman spectra with 1064nm excitation; The Specac Variable Temperature Cell (PIN 21525) was originally designed for FT -IR transmission studies of liquid or solid samples at various temperatures ranging from -190°C to 250°C. The cell consists of a vacuum refrigerant dewarlcell holder assembly. The Photoluminescence Spectra were measured using Ar+ laser 488 nm with a power of 90 mW and the spot area of the laser beam was about 2mm, the laser beam is incident up on a mirror which reflects it to the sample then reflected by a spherical mirror to the monochromator, filter OG 515 is used. The filtered output signal (PL signal) was introduced to the slit of the monochromator

69

of a length of 750 mm [SPEX 750M] with a grating (1200 grimm), the resolution of the monochromator is I AD. The PL signal was detected by photomultiplier detector (185-850nm) uvglass; the output signal was amplified using the lock-in technique [SR51O] where the laser beam was chopped mechanically while the reference signal having the same frequency of the chopped beam was connected to the input of the lock-in amplifier. The PL signal was connected (output of the detector) to the input of the amplifier while the output of the amplifier was a displayed using the computer software program. The sample was placed in the pumped liquid helium path cryostat (CTICRYOGENICS), with an electrical heater (SCIENTIFIC INSTRUMENT INC. 9620-1) and control equipment, to reach and hold any temperature from 8K to 300K.

3. Results and Discussion It was observed that the emission lines of Zn, Se and Te were present in the energy range investigated (0-20 Ke V) which is represented in Fig. (1) and the chemical composition results of ZnSe xTel_x are shown in Table (1).

Table (I) Chemical composition of ZnSe xTel_ x by EDX

Atomic Percentage Se

Te

Zn

0

0.00

50.18

49.82

0.038

1.85

46.31

51.84

0.048

2.33

46.15

51.52

0.166

7.54

37.98

54.48

0.202

8.93

35.22

55.85

I

34.94

0.00

65.06

70

200

Zn

100

h __________ x= 0 _ ,L,,

o

~

100

x=O.048

x=O.166 108

50

x=O.202 101l

Se

x=1

o

o

5

10

15

Energy (KeV)

Fig. (I) Energy Dispersive X-ray Analysis EDX of ZnSe, Tel_x

20

71

1- Raman Spectra: ZnSe Single Crystal The room temperature Raman spectrum of ZnSe single crystal showed bands at 140.8,208,251.2 cm", which could be assigned as 2TA, TO, LO respectively. The obtained longitudinal optical (LO) and the transverse optical (TO) of ZnSe crystal are in good agreement with the previous work [9, 10, 11]. Temperature dependence Raman spectra of ZnSe were carried out in the temperature range from liquid nitrogen temperature up to 358 K as shown in Fig. (2). ZnSe 0.06 '. , - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ,

-358K -348K -323K -273K -223K 173K 153 K 123K -113K

0.05

0.04

~ 0.03

0.02

0.01

50

1DO

150

200

250

300

350

4DO

450

5DO

Waven umber (Crn-1)

Fig. (2) Temperature dependence Raman spectra of ZnSe

The vibrational spectral bands are characterized by three parameters I( v), v and D.v. The variation of each parameter with temperature might help in understanding the temperature behavior of ZnSe crystal. Studying the temperature dependence of each parameter yielded the following: Studying the 2T A mode shows that the 2TA shifts to lower phonon energy as the temperature increases and intensity as well as its spectral width increases with increasing the temperature as shown in Fig. 3(a, b, c). Studying the LO mode shows that the LO shifts to lower phonon energy as the temperature increases and intensity as well as its spectral width increases with increasing the temperatUFe as shown in Fig. 4(a, b, c).

72

(a) -_._------------_._-----_.-_._- -

150 148 146 144

E

S?-

142

" t1 0

140

0

138

"'"

136

a.

134

e

" e

"

e

e

e

e e

Cl.

''""

132 0.~28

•

(b) 0.020

•

•

::i

~0.Q15

~

• •

U)

" 0.010

l!l E

••

0.005

•

(c)

0.080

•

45 40

•

35

E

S?-

30

I

25

s:

•

•

::;

•

•

"- 20 15

•

10 100

•

•

150

200

250

300

350

T (K)

Fig. 3(a, b, c) The temperature dependence of the band parameters of 2TA bands

400

73

(a) 255

•

254

•

E 253

8 c 0

t50

• • •

252

Co

-"

•

•

Cll 251
c..

250

•

•

0.06

(b)

0.05

0.04 :J

"

i

" "

"

"

; 0.03 'iii

c

2

.s

0.02

""

"

0.01

" II(I)Q

(C)

9.5

x x

9.0

x x

8.5

E

8.0

::2:

7.5

8

x x x x

I

:s:lJ..

7.0 6.5 6.0

x

5.5 100

150

200

250

300

350

T(K)

Fig. 4(a, b, c) The temperature dependence of the band parameters of LO

400

74 However we recommend that you keep an initial version of this file for the shift of Raman modes with temperature is a manifestation of anharmonicity in the vibrational potential energy, which results in the decay of phonons into vibrations of lower frequencies. As shown in Fig. 3(a), Fig. 4(a). The influence of temperature on the phonon energy determined by Raman scattering is primarily connected with the thermal expansion of the crystal lattice [121. The FWHM of Raman modes increases with increasing the temperature, as shown in Fig. 3( c) and Fig. 4( c), this increase in the spectral line width may be attributed to increasing the decay rate of phonon into some phonons with lower energies due to phonon-phonon interaction 1121 .

2- Raman Spectra of ZnSeTe Samples In order to account for the effect of substitution of Te by Se on the Raman bands we considered samples of the type ZnSe xTel.x having x = 0, 0.038, 0.048, 0.166, 0.202 and I where x is the percent of selenium as shown in Fig. 5, the variations occurring in the vibrational bands of the component Zn Sex Te I,x for the mentioned above 6 values. Analysis of the Raman spectra of the component under the investigation shows that: The 2TA mode appears at 140.6 cm'l at ZnSe shifted in a linear manner to 109 cm' l and Fig. (6) shows the linear dependence of the peak position (1I) on the concentration of Se. The same behavior was obtained for the other two modes of 175.6 cm,l and 251 cm' l almost with the same rate as shown in Fig. (7) . Our results showed that

75

0.1 0 .04 0.0 0 .02

-

0.04 0.00

::J

~ 0.02

-

>- 0 .06 .!Q 0.00 c Q)

C 0 .03 0.4 0.00 0.3 0.2

OOOS 0.0 0.03

0 .00 0

100

200

300

400

wavelength (Cm"1)

Fig. 5 Raman Spectra of ZnSexTe \.x at room temperature

500

76 the dependence of the band position on the concentration of Se in the matrix is having general trend. That the shifting of 2T A, LO, TO from ZnTe where its WLo = 204.4 cm -I and WTo = 177.S cm -I (which agree with ref. [13]) to ZnSe where its WLo = 251.2 cm -I and WTo = 20S cm -I and the various concentration of Se obey linear behavior .Bearing in mind that the ZnSe is in the form of single crystal while ZnSeTe sample are in the polycrystalline phase.

145~-----------------------------------------------,

140 135

~ 130 ~

i; 125 Cii

c: Q)

120

,g

115

c: o c:

a. 110

105

100L-------------__- -__- - - - - - - -__- - - - - - - -__- - - -__--~ 0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

concentration(se percent)

Fig. (6) The band position 2TA with Se concentration

0.9

77

0.0

0.2

0.6

0.4

0.8

1.0

250

E 240

~ >.

LO

~ 230 Q) c:

*

Q)

c: 220 o c: ~ 210

a..

**

200~--------------------------------------~

210 205

E 200

~

~

....

TO 195

~ 190

Q)

§

185

c:

~

a..

180

175

181

0.0

0.2

0.4

0.6

0.8

1.0

X of Zn Sex Te 1 _x

Fig. (7) The band position LO, TO with Se concentration

The ternary materials 1141 show difference composItIon behaviors dependent on the differences in the masses of the element Se and Te (i .e. on the existence of an energy -forbidden gap between the optical phonon frequencies of the binary materials ZnSe and ZnTe). For material like ZnSeTe, the LO mode of

78 pure ZnTe changes into the LO mode of pure ZnSe with increasing Se content and the TO mode of ZnTe changes into the TO mode of ZnSe. This behavior is called single or one-mode behavior. Raman studies show that the lattice dynamics are characteristic of single-vibrational-mode behavior over the entire alloy range.

4-1 Photoluminescence measurements In order to choose the excitation line, we measure the absorbance of the samples using spectrometer (YARIAN Cary BIO 50) in the range 200 nm to 900nm as shown in Fig. (8), and we observed maximum absorbance in the range 200-500 and any excitation line in the range can be used as an excitation source. 1.8 , . - - - - - - - - - - - - - - - - - - - - - - - - - = = == -x=o

- x=O.038 -x=O,048

1.6

200

300

400

500

600

700

800

Wavelength (nm)

Fig. (8) The Absorbance of ZnSe xTel -x Crystals

The energy gap calculated from the absorbance measurements and fitted to Yegard's law at room temperature, Yegard's law states that Eg(x)=a+ b x+ c x 2 where Eg(x) is the band gap of ZnSexTel_x using Eg(O) the optical energy gap of ZnTe which equal to 2.26 ey1151, Eg(1) the optical energy gap of ZnSe which equal to 2.67 1161 at room temperature and Eg(Se=0.68)=2.18 ey1171, by substituting in Yegard's law for determining the constants a, band c from the three equations. We get the following equation: Eg(x) =2.26-1 .238x+ 1.648x 2

79

2.9 • Vegard's law • experimental

2.7

-

Poly. (Vegard's law)

-

Poly. (experimental)

2.5

2.3 :>~ C1

w

-

2.1

1.9

1.7

1.5

°

0.2

0.4

0.6

0.8

1.2

x (the percent of Se in ZnSe(x) Te(1-x))

Fig. (9) Energy Gap measurement as a function of x

First we used HeCd laser with a wavelength 326 nm as an excitation source to measure the Photoluminescence of ZnSexTel_x but no excitonic peaks and no clear spectra were observed, this may be due to the poor crystallinity of the samples and the relatively low power 10 mW of the HeCd laser. The PL spectra of ZnSexTel_x Crystals were measured in the 500-950 nm wavelengths using Ar+ laser of wavelength 488 nm. At a constant excitation laser intensity 90 mW . The low temperature PL measurements of our ZnSexTel_x at 25 K are shown in Fig_ (10).

80

20

ZnTe

19 18 17 - - x=0.038

16 15 14 13 ~

::J

.i ~

'00

12 11 10

c

9

C

8

Q)

7 6 5 4 3 2 0 500

600

700

800

900

1000

Wavelength (nm)

Fig. (10) The low temperature PL measurements of ZnSexTe l_x at 25 K

Where the broad bands of the ZnSe xTe., are summarized in the following table (2). And DAP is observed about 2.3 eV are summarized in table (3).

81

Table (2) The broad bands of the ZnSe xTe_ x at 25 K the main broad band x

the assignments

A (nm)

Ref.

Eg(eV)

0

663.2

1.868

0.038

623

1.989

0.048

680

1.822

0.166

595.25

2.081

[ 19]

0.202

587

2.111

[19]

1

695

1.783

[18]

[ 18] self activated (SA)

Table (3) DAP is observed about 2.3 eV at 25 K the band x

A (nm)

the assignments

Ref.

(DAP) about 2.3 eV

[ 18]

Eg(eV)

0

539

2.299

0.048

535

2.316

0.202

542

2.286

1

539

2.299

Deep level emission of Zn (SA) observed in both ZnSe and ZnTe, But the y band is observed in ZnSe, ZnTe and at x=0.048. The appearance of this band might be attributed to the lattice imperfection; this y band was observed in other II-VI semiconductors l20I .

82 The broad self activated (SA) emission band has been assigned to various crystalline defects, such as dislocations and vacancies or their combination with impurities! 19!.

Conclusion The room temperature Raman spectrum of ZnSe single crystal showed bands at 140.8,208,251.2 cm- I , which could be assigned to 2TA, TO, LO respectively. The shift of Raman modes with temperature is a manifestation of anharmonicity in the vibrational potential energy, which results in the decay of phonons into vibrations of lower frequencies. The FWHM of Raman modes increased with increasing the temperature, this increase in the spectral line width may be attributed to increasing the decay rate of phonon into some phonons with lower energies due to phonon-phonon interaction. The influence of temperature on the phonon energy determined by Raman scattering is primarily connected with the thermal expansion of the crystal lattice. The dependence of the band position on the concentration of Se in the matrix is having general trend as that of the peak position. The shifting of 2T A, LO, TO from ZnTe where its O)Lo = 204.4 cm- I and O)To = 177.8 cm- l to ZnSe where its O)Lo = 251.2 cm- I and O)To = 208 cm- I and the various concentration of Se obeys linear behavior .Bearing in our mind that the ZnSe is in the form of single crystal while ZnSeTe sample are in the polycrystalline phase. The LO mode of pure ZnTe changes into the LO mode of pure ZnSe with increasing Se content and the ZnTe TO changes into the ZnSe TO. This behavior is called single or one-mode behavior. Raman studies showed that the lattice dynamics are characteristic of single-vibrational-mode behavior over the entire alloy range. Low-Temperature Photoluminescence (PL) spectra were measured on six samples, the spectra of ZnSexTel_x showed a broad band which may be attributed to self activated emission. The broad self activated(SA) emission band have been assigned to various crystalline defects, such as dislocations and vacancies or their combination with impurities. DAP is observed about 2.3 eV at x=O, 0.048, 0.202 and 1. The band of a self activated (SA) photoluminescence is properly studied in A2B6 compounds. It is a donor -acceptor recombination nature and is determined to DA associate {V Zn +D+)O as acceptor, with the components in the nearest points in a unit cell .

83

References [1]

W. Lin, X. Yang, S.P. Guo, AElmoumni, F. Fernandez, and M.e. Tamargo, Appl. Phys. Lett. 75, 2608 (1999). [2] D. Albert, J. NUrnburger, V. HHock, M. Ehinger, W. Faschinger, and G.landwehr, Appl. Phys. Lett. 74, 1957 (1999). [3] D. Huang, e. Jin, D. Wang, X. Liu, J. Wang, X. Wang, Appl. Phys. Lett. 67 (1995) 3611. [4] L.K. Vodop'yanov, E.A. Vinogradov, N.N. Melnik, V.G. lotnitchenko, J. Chevallier, J.e. Guillaume, J. Phys.(France) 39 (1978) 627. [5] S. Nakashima, T. Fukumoto, A Mitsuishi, 1. Phys. Soc. Jpn 30 (1978) 1508. [6] AJ. Pal, 1. Mandai, 1. Alloys Compounds 216 (1995) 265. [7] A Kamata, H. Yoshida, S. Chichibu, H. Nakanishi, J. Crystal Growth 170 (1997) 518. [8] V.Yu Davydov, et al Proc. Int. Workshop on Nitride semiconductors IPAP Conf.series pp 657-660. [9] FJ. Wang, D. Huang, XJ. Wang, X.X. Gu and G.e. Yu, 1. Phys.: Condens. Matter 14 No 21 (3 June 2002) 5419-5431. [10] D. Sarigiannis, J.D. Pecj, TJ. Mountziaris, G. Kioseoglou, A. Petrou. MRS Proceedings, v .616, 41-46, 2000. [11] Ja-Chin Jan, Shou-Yi Kuo, Sun-Bin Yin and Wen-Feng Hsieh. , Chinese Journal of Physics Vo1.39, No.1 February 2001. [12] M. Szybowicz, M. Kozielski, F. Firstz, S. Legowski, H. Meczynska, Cryst. Res. Technol. 38, No. 3-5, (2003) 359-365. [ 13] J. Camacho, A Cantarero, I. Hermindez-Calder6n and L. Gonzalez, Journal of Applied Physics (November 15, 2002 ) Volume 92, Issue 10, pp. 60146018. [14] Lan R. Lewis, Howell G.M. Edwards, "Hand book of Raman Spectroscopy", Chapter 12 (Bianca Schreder and Wolfdand Kiefer). [15] T. Mahalingam, V.S. John and PJ . Sebastian, 1. Phys.: Condens. Matter 14(2002) 5367-5375. [16] S. Darwish, AS. Riad and H.S. Soliman, Semicond. Sci. Techno1.1995 (10) 1-7. [17] Ching-Hua Su, S. Feth, Shen Zhu and S.L. Lehoczky, J. Appl. Phys. Vol. 88, No.9 (Nov. 2000) 5148-5152. [18] Choon-Ho Lee, Gyoung-Nam Jeon, Seung-Cheol Yu and Seok-Yong Ko, J. Phys. D: Appl. Phys. 28 (1995) 1951-1957. [19] Q. Liu, H. Lakner, e. Mendorf, W. Taudt, M. Heuken, K. Heime, J. Phys. D: Appl. Phys. 31(1998)2421-2425.

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AUTOMATED POLARIZATION-DISCRIMINATION TECHNIQUE TO MINIMIZE LIDAR DETECTED SKYLIGHT BACKGROUND NOISE, PART I

YASSER Y. HASSEBO'

Math/Engineering Dept., LaGuardia Community College of the City University of New York 31-10 Thomson Ave., Long 1sland City, NY 11101, USA

KHALED ELSA YED

Department of Physics, Faculty of Science, Cairo University, Egypt

SAMIRAHMED

Remote Sensing Lab, The City College of the City University of New York Convent Ave, New York, NY 10031, USA Much research has been done on lidar Signal-to-Noise Ratio (SNR) improvements, particularly for lidar daytime operations. Skylight background noise confines lidar daytime operations and disturbs the measurement sensitivity. Polarization selective lidar systems have, formerly, been used mostly for separating and analyzing polarization of lidar returns for a variety of purposes. In our previous work, we devised in the remote sensing laboratory at the City College of New York a pOlarization discrimination technique to maximize lidar detected SNR taking advantage of the natural polarization properties of scattered skylight radiation to track and minimize detected sky background noise (BOS). This tracking technique was achieved by rotating, manually, a combination of polarizer and analyzer on both the lidar transmitter and receiver subsystems, respectively. The polarization orientation at which the minimum BOS occurs, follows the solar azimuth angle, even for high aerosol loading. This has been confirmed both theoretically, assuming single scattering theory, and experimentally. In this article, a design to automate the polarization discrimination technique by real time tracking of the azimuth angle to attain the maximum lidar SNR is presented. With an appropriate control system, it would then be possible to track the minimum BOS by rotating the detector analyzer and the transmission polarizer simultaneously, achieving the same manually produced results. Analytical results for New York City are summarized and an approach for applying the proposed design globally is investigated. Keywords: Polarization, Control System, Lidar SNR Remote Sensing, Skylight noise, Azimuth Angle.

* [email protected], Tel: +1 (718) 482-6092, Cell: +1 (917) 403-0512, Fax: +1 (718) 6092059

85

86 1. Introduction

Polarization selective lidar systems have, formerly, been used mostly for separating and analyzing polarization of lidar returns, for a variety of purposes, including examination of multiple scattering effects and for differentiating between different atmospheric scatterers and aerosols. 1·6 For instance, Polarization Diversity Lidars (PDL is a lidar with two channels to detect two polarizations) 7·8 are famous lidars to measure and detect clouds. Mie scattering is the basic theory to distinguish between cloud phases (liquid and solid) where the backscattering from non-spherical (e.g., crystal phase) particles changes the polarization strongly, but the spherical (water droplets) particles do not. 9 Both spherical and non-spherical cloud particles have a degree of depolarization (J = I II ) due to the multiple scattering effects, where I l are .L

II

L'

II

respectively the perpendicular and the parallel intensity components for the incident light. It is well known that the degree of depolarization in non-spherical cloud particles is greater than the degree of depolarization of spherical particles depolarization (5., )5, ). Previously, we succeeded in extending the polarization lidar approach to improve lidar Signal-to-Noise (SNR). 13· 16 In our efforts, among others, to improve lidar SNR, we devised a manual polarization selective scheme to reduce the sky background signal (BOS). This approach led to improvements in SNR up to 300% and attainable Ii dar ranges improvement above 30%, which are important considerations in daylight lidar operations. The principles of operation for the polarization discrimination technique are well-documented 13· 16 and are reviewed briefly below. The approach discussed in our polarization selective scheme is based on the fact that most of the energy in linearly polarized elastically backscattered lidar signals retains the transmitted polarization I, 6, while the received sky background power observed by the lidar receiver shows polarization characteristics that depend on both (1) the scattering angle e" between the direction of the lidar and the direct sunlight, and (2) the orientation of the detector polarization relative to the scattering plane. In particular, the sky background signal (BOS) is minimized in the plane parallel to the scattering plane, while the difference between the in-plane component and the perpendicular components (i.e., degree of polarization) depends solely on the scattering angle. For a vertically pointing lidar, the scattering angle Bsc is the same as solar zenith angle e,. The degree of polarization of sky background signal observed by the lidar is largest for solar zenith angles near Os == 90" and smallest at solar noon. 10·12 The essence of the approach (previously reported) is therefore to first determine, manually, the parallel component of the detected sky background signal (BOS) with a polarizing analyzer on the receiver, thus minimizing the detected BOS. This parallel component in a scattering plane makes an angle equal to the azimuth angle with respect to the reference axis. Simultaneously we orient manually the polarization of the outgoing lidar signal

87 so that the polarization of the received lidar backscatter signal is aligned with the receiver polarizing analyzer. This ensures unhindered passage of the primary lidar backscatter returns, while at the same time minimizing the received sky background signal (BGS), and thus maximizing both SNR and attainable lidar ranges. The system geometry and measurements approach for the polarization discrimination scheme is weB-documented 13-16 in our previous publications. Section 2 introduces Polarization selective scheme globalization. Diurnal variations in BGS as functions of different solar angles are given and the SNR improvement is shown to be consistent with the results predicted from the measured degree of linear polarization, with maximum improvement restricted to the early morning and late afternoon. Automated control system will present in Section 3, where the proposed controller instruments and the model description will be discussed. Conclusions and discussion are presented in Section 4

2.

Polarization Selective Scheme Globalization Solar Zenith Angle Impact on SNR The SNR improvement factor ( G

imp )

is plotted as a function of the

local time, Figure 1a, and the solar zenith angle, Figure 1b. Since the solar zenith angle retraces itself as the sun passes through solar noon , it would be expected that the improvement factor (G imp ) would be symmetric before and after the solar noon and depend solely on the solar zenith angle. This symmetry is observed in Figures 1a and 1b for measurements made on 19 February 2005 and is supported by the relatively small changes in optical depth (AOD) values obtained from a collocated shadow band radiometer, (morning 't =0 .08, afternoon 't = 0.11 )

-

/,ooJ

lL

"'-

:, ~~ . .

r--

1

-

J

G I",

Figure lea). G imp in detection wavelength of Figure l(b). G im" in detection wavelength of 532 nm verses local time (NYC EST) on Feb 19.05 532 nm verses solar zenith angle on Feb 19.05

88

Solar Azimuth Angle Impact On SNR While the magnitude of the SNR improvement factor is to some extend diminished due to scattering and depolarization, it is still important to confirm if the scattering plane defining the maximum and minimum polarization states has changed. Within the single scattering theory, the polarization orientation at which the minimum BGS occurs should equal the azimuth angle of the sun (see previous papers 13.16). To validate this result, the polarizer rotation angle was tracked (by rotating the detector analyzer) over several seasons since February 2004 and compared with the azimuth angle calculated using the U.S. Naval Observatory standard solar position calculator 21 (14 April 2005). As expected, the polarizer rotation angle needed to achieve a minimum BGS closely tracks the azimuth angle as shown in Figure 2.

_ _ Azimuth .ngle

i

___ -

Pol.rl~.r

rot..tlnliil angle

[). ...... 240

--~

~ --+----+_-+-----+.~_+___+_-+__---+--~

+-1-----.

Azimuth

ngle

'---i

_---,

/ ,~ '----I----+-/~

------

/

Loca, Tim.

Figure 2. Comparison between solar azimuth angle and angle of polarization rotation needed to achieve minimum Ph: 14 April 2005

While it is intuitive that the maximum noise suppression should occur when the receiver polarization is parallel to the scattering plane in the single scattering regime, we have also examined the orientation of the scattering plane for the case of multiple scattering. However, we confirmed that even for high optical depth (multiple scattering regimer 0" = 0.5 ), the maximum noise improvement factor occurs when the differential azimuth angle is zero (i.e. the scattering plane and the observation plane are the same). \3·16 This relationship is significant since it allows us to design an automated approach that makes use of a pre-calculated solar azimuth angle as a function of time and date to automatically rotate and set both the transmitted lidar polarization and the detector polarizer at the orientations needed to minimize BGS. With an appropriate control system, it would then be possible to track the minimum BGS by rotating the detector analyzer and the transmission polarizer simultaneously to maximize the SNR, achieving the same results as would be done manually as described above. An integration of an automated approach is proposed in the following section.

89 3. Automated Control System The approach proposed here is a global shared control system that can be used with !idar virtually for all ground-based, in situ probes (airborne), and spacebased !idar platforms. In this paper, we concentrate on typicallidar ground based stations. By knowing the longitude, the latitude and the azimuth angles during a given day, an optimization system can be applied to maximize !idar signal-tonoise ratio and corresponding !idar range automatically. We are proposing a design for an automated negative feedback position control system to minimize !idar BGS and maximize the SNR and its attainable range using our polarization discrimination 'technique which device by us previously. 13-16 The main advantages of this automated control system are: potential for automated data collection, fast and accurate lidar operations, applicability to different !idar configurations (vertically pointing and scanning lidars) and for different types of !idar returns (Rayleigh, Mie, Raman, DIAL, Doppler, and florescence lidars, and globalization. Finally, in the new era of remote sensing including ground-based, in situ probes (airborne), and space-based !idar platforms, this approach can be adopted, with some differences, to many space borne applications. In section 3.1 the typical information exchange between lidar devices is discussed. The control system design process is introduced in section 3.2. In section 3.3 the proposed controller instrument is discussed. Finally, in section 3.4 the control model is described.

A Typical Information Exchange Between Lidar Subsystems • •

• •

The research presented in this paper is based on the following !idar parameters, hypothesis and assumptions: The experimental results are to be carried out with monostatic (coaxial in the lab and biaxial in the vehicle) elastic (Mie and Rayleigh) scattering lidars, for which the wavelength of backscattered observation is the same as that of the laser The lidars used are !idars operating in the Visible spectral range. All experimental results shown above were taken during the daytime operations at the CCNY site, USA (longitude 73.94 W, latitude 40.83

N) • •

The polarization is assumed to be linear polarization (the polarizer is to pass a single polarization and extinguish the orthogonal polarization) The single scattering regime and clear sky conditions were assumed

Figure 3 shows typical information exchanges needed, and which summarizes the interactions used as the basis for the control model operation.

90

Figure 3. Typical information interactions between lidar devices

Flow for Azimuth Angle and Position Correction The first step in a control system design is to obtain a configuration, identification of the key components of the proposed lidar system to meet a requirement 'goal". In this section we introduce the sequential design of an automated negative feedback position control system to improve Iidar SNR. This includes the controller goal, the variable parameter to be controlled, proposed hardware to be used in the control system, and finally the flow for the system setup and the SNR experiment. Controller Goals 1- Minimize the lidar BGS 2- Maximize the Lidar return signal 3- Control system with fast response and accurate results Components to be control: Generally, the lidar optical components and the electronic devices are discussed in section two and listed in table I. We fixed most of these components and devices except the components that we desired to control. These components to be controlled are: • • •

The polarization device at the receiver subsystem The polarization device at the transmitter subsystem Power-meter at the receiver subsystem

91

Proposed Controller Instruments The polarization devices at both subsystems are mounted on the rotation stages. Since we wish to rotate the polarizer at the receiver according to the azimuth angle, we select a rotation stage as the actuator. These stages can be controlled using controller devices as shown in Fig 4 and Fig 5. Programmable logic control (PLC) can be also used as a controller. Also since the microprocessor calculation speed is fast compared to the rate of change of the azimuth angle and the input signal we can consider a microprocessor as a good position controller model with very accurate measurements. A well-known closed loop position control model is the PICOMETER closed loop driver model 8751-C and! or 8753. This model and its communications adapter cables, and the setup 22 are shown in Fig. 5 and 6.

Device to control

Desired position (voltage)

Process

Actual position

+ Measyred position (voltage) Power-meter Feed back Sensor

Figure 4. Block diagram of a negative feedback position control system to minimize lidar BGS

Model 8722 ClJfflm AdflpflY

~·· · ·i~ ~,I !

Modet8721

to'

COlt)'1/.

Cab/tJ,

t

MocfeI8351

nJ?Y Picomota* AdWlIY

Mod4I!SJOX or 8310 PJcc)m~AcrlRJtQf"5

~ CIJbb Prov£Jed ; t Mifl Power SLpfNy

'- - - '

~~~~ Mocs.f$1$1

Modni 6752

ipk;-oJ Joystick

floomet ConlroiMF M06IrI8723 3' COOlm (''sbiil

5~

ModGI8401

RCf;XY Smge

Model 8724 One Of M0f8 Comm OIbfe(s) 1Aodei$7$311ndlOl' Moct.t8751-C iPk;o Drlier(.s-)

Figure 5: The Intelligent Picomotor network can be configured for different motion control applications 22 (User's Guide: Intelligent Picomotor Control Modules)

92

(a)

(D)

Figure 6. (a) Model 8751-C Closed- Loop Driver With (b) Model 8310 Closed-Loop Picomotor 22

Model Description We have developed an instrument control model design suitable for simulating a sequential theoretical design of an automated negative feedback position control system to minimize lidar sky background signal (BGS) and maximize the SNR and its attainable range. The model can be described in four stages. The first stage deals with creating a source data pool (such as date, time and the corresponding azimuth angle, and location), and then prepares the system to start. The second stage explains how to minimizing BGS at the receiver subsystem. The third stage describes how to maintain a maximum lidar return using a polarizer at the lidar transmitter subsystem. Finally the fourth stage illustrates data collection and processing. The flow chart of this proposed design is presented in Figure 7.

Model flow Stage 1: Creating a source data pool 1- Get the lidar lab longitude and latitude 2- Create a data pool for the azimuth angle for this position according to date and time (lO minuets step) 3- Reset control system timer Stage 2: Minimizing BGS at the receiver 4- Block the lidar transmitted beam 5- Get the azimuth angle from the data pool 6- Rotate the polarization device at the receiver subsystem according the azimuth angle 7- Measures the BGS (use it as an offset) Stage 3: Maximizing lidar return signal 8- Unblock the transmitted beam 9- Measure the lidar return signal 10- Rotate the polarization device at the transmitter subsystem to maximize the lidar return signal (use a "For loop" supported with Power-meter and/or Labview interface) Stage 4: Data collection! processing 11- Start collecting/saving lidar data 12- Stop saving after 8 mins

93

13- Check control system timer to start the second period of measurement exactly after 10 mins from the previous period 14- Repeat steps 4 to 13

/' l - - I

Sl \

!

(!) \

f ~ \

- /- - -- ---"' - - - --------;7 Get new time and Azimuth angle

"\ 1

I 1

1 CO \

I

1 (]) \

1

( 'E .- \\

1 J

I.f;;; \

\~.l _____ _

I

"\ 1 1 I

1

J

I

/'c

l-------

_f*----~

( 0\\ (

1

.-

"\

:s \

( 1

18\

( al \

! 10 \ I Cl \

1

I

\

1

1

T >10 mins ___-N-O~

'... . .l _____ _

J

I

Figure 7: Flow chart for automated lidar system setup and the SNR improvement

94 4. Conclusion and Discussion A polarization discrimination technique was used to maximize lidar detected SNR taking advantage of the natural properties of the scattered skylight radiation to track and minimize detected sky background noise (BGS). This tracking technique was achieved in the previous work by rotating, manually, a combination of polarizer and analyzer on both the lidar transmitter and receiver subsystems, respectively. Lidar elastic backscatter measurements at 532 nm, carried out continuously, but manually, during daylight hours, and showed a factor of .JW improvement in signal-to-noise ratio and the attainable lidar range up to 34% over conventional un-polarized schemes .. In this article, a design for an automated negative feedback position control system to minimize lidar sky background signal (BGS) and maximize the SNR and its attainable range was presented and the same factor of improvement of SNR was established. This approach can be employed for any place and time. This can be achieved by knowing the longitude, the latitude and the azimuth angles during a given day in a certain location. The main advantages of this automated control system are: potential for automated data collection, fast and accurate lidar operations, applicability to different lidar configurations (vertically pointing and scanning lidar), and for different types of lidar returns (Rayleigh, Mie, Raman, DIAL, Doppler, and florescence lidars), and globalization, as well as to lidars operated on aircraft or space platforms, with some differences, such as the A-Train.

Acknowledgements This work is partly supported by a 2007-2008 Professional Development Grant administered by the Educational Development Initiative Team (EDIT) of LaGuardia Community Collage.

References 1.

2. 3. 4.

5.

6.

R. M. Schotland, K. Sassen, and R. 1. Stone, "Observations by lidar of linear depolarization ratios by hydrometeors," 1. Appl. Meteorol. 10, 10111017, (1971) K. Sassen, "Depolarization of laser light backscattered by artificial clouds, " Appl. Mete. 13,923-933 (1974) C. M. R. Platt, "Lidar observation of a mixed-phase altostratus cloud," 1. Appl. Meteorol. 16,339-345 (1977) K. Sassen, "Scattering of polarized laser light by water droplet, mixedphase and ice crystal clouds. 2. Angular depolarization and multiple scatter behavior," 1. Atmos. Sci. 36, 852-861 (1979) C. M. R. Platt, "Transmission and reflectivity of ice clouds by active probing," in Clouds, Their Formation, Optical Properties, and Effects, P. V. Hobbs, ed. Academic, San Diego, Calif., 407-436 (1981) Kokkinos, D. S., Ahmed, S. A. "Atmospheric depolarization of lidar backscatter signals" Lasers '88; Proceedings of the International

95

7. 8.

9. 10. 11. 12.

13.

14.

15.

16.

17.

18.

19.

20. 21. 22.

Conference, Lake Tahoe, NV, A90-30956 12-36, McLean, VA, STS Press, 538-545 (1989) G.P.Gobbi, "Polarization lidar returns from aerosols and thin clouds: a framework for the analysis," Appl. Opt. 37,5505-5508 (1998) N. Roy, G. Roy, L. R. Bissonnette, and J. Simard, "Measurement of the azimuthal dependence of cross-polarized lidar returns and its relation to optical depth," Appl. Opt. 43,2777-2785 (2004) J. Hansen, and L. Travis, "Light Scattering in Planetary Atmospheres, "Space Science R. 16,527-610 (1974) Takashi Fhjii and T. Fukuchi. Laser Remote Sensing, Taylor and Francis Group (2005) Sassen, K. "Advanced in polarization diversity lidar for cloud remote sensing." Proc. IEEE 82: 1907-1914 (1994). Sassen, H. Z. K., et al. "Simulated polarization diversity lidar returns from water and precipitating mixed phase clouds." Appl. Opt. 31: 2914-2923 (1992). Yasser Y. Hassebo, Barry Gross, Min 00, Fred Moshary, and Samir Ahmed "Polarization discrimination technique to maximize lidar signal-tonoise ratio for daylight operations" Appl. Opt. 45, 5521-5531 (2006) Yasser Y. Hassebo, B. Gross, F. Moshary, Y. Zhao, S. Ahmed "Polarization discrimination technique to maximize LIDAR signal-to-noise ratio" in Polarization Science and Remote Sensing I/, Joseph A. Shaw, J. Scott Tyo, eds., Proc. SP/E 5888,93-101 (2005) Yasser Y. Hassebo, Barry M. Gross, Min M. 00, Fred Moshary, Samir A. Ahmed "Impact on lidar system parameters of polarization selection I tracking scheme to reduce daylight noise" in Lidar Technologies, Techniques, and Measurements for Atmospheric Remote Sensing, Upendra N. Singh, ed., Proc. SP/E 5984, 53-64 (2005) S. Ahmed, Y. Hassebo, B. Gross, M. 00, F. Moshary, "Examination of Reductions in Detected Skylight Background Signal Attainable in Elastic Backscatter Lidar Systems Using Polarization Selection", in 23rd International Laser Radar Conference (ILRC), Japan (2006) Agishev, R. R. and a. A. Comeron "Spatial filtering efficiency of monostatic biaxial lidar: analysis and applications." App. Opt. 41: 75167521 (2002). Yasser Hassebo, Ravil Agishev, F. Moshary, S. Ahmed, Optimization of biaxial Raman lidar receivers to the overlap factor effect, in the Third Annual NOAA CREST Symposium Hampton Virginia, USA, April (2004) Yasser Hassebo, Khaled El Sayed, "The Impact of Receiver Aperture Design and Telescope Properties on lidar Signal-to-Noise Ratio Improvements", in AlP Conference Proceedings 888,207-212 (2007) Welton, E., J. Campble, et al. First Annual Report: The Micro-pulse Lidar Worldwide Observational Network, Project Report (2001). Solar Calculator Webpage: http://aa.usno.navy.mil/dataidocs/AltAz.html User's Guide: Intelligent Picomotor Control Modules

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LASER INTERFEROMETRIC MEASUREMENTS OF THE PHYSICAL PROPERTIES FOR He, Ne GASES AND THEIR MIXTURE N. M. ABDEL-MONIEM Physics Department, Faculty of Science, Tanta University, Egypt M. M El-MASRY, B. EL-BRADIE AND F. M. EL-MEKA WY Laser Physics Laboratory, Physics Department, Faculty of Science, TanIa University, Egypt A Mach-Zehner interferometer MZI illuminated with He-Ne Laser 632.8nm is used for measuring the refractive index for He. Ne gases and their mixture HeNe. The measurements are carried out at different pressures and temperatures. The error factors of the refractive index measurements for He. Ne and HeNe gases are equal to ±1.7xlO-5 • ±9.SxlO- 6 and ±7.2SxIO- 5 respectively. Some calculations of the electrical properties are carried out such as the optical permittivity dielectric susceptibility and specitic refractivity from the determination of the refracti ve index. Also. the molecular radii of the gases under investigation are computed then the transport coefficients (diffusion. viscosity and thermal conductivity) are calculated. All of these calculations are carried out at different pressures and temperatures. The experimental results of refractive index for the above mixture are compared with the results estimated using one of the mixing rules and a good agreement is achieved. Also. some physical parameters are compared with other values in another literatures.

1.

Introduction

The inert gases are excellent as filling gases for electrical discharges, since they do not react with the electrodes and tubes containing them. Both helium and argon are available in industrial quantities which they are used in welding to shield the hot metal from the atmosphere, especially in the case of reactive metals. Helium is often used as an inert atmosphere in growing semiconductor crystals and for similar processes. It has small atomic mass which leads to large thermal velocities, rapid diffusion and easy heat transfer. The rapid diffusion makes helium a good carrier gas for gas chromatography. Helium is also used as a driver gas in hypersonic wind tunnels. The high thermal conductivity and its zero neutron capture cross section make helium a good coolant in gas-cooled nuclear reactors, though its low density works against it. A mixture of gases is common for many applications. A discharge through a mixture of helium and neon creates a population inversion in the neon that can be used in a laser. The laser has made a tremendous impact on science and technology. During this time, laser based research has undergone rapid development and has seen wide use due to its unique properties through forty years old, the non-contact nature of laser-based techniques makes them valuably unique.

97

98 Non-contact measurement techniques have played a significant role in the investigation of thermal and fluid phenomena. The most popular aser-based techniques are the laser interferometer technique ll .S1 .

2.

Theoretical Background

In this paper, the relation between the refractive index and all parameters are presented. The refractive index of a transparent optical medium is defined as a factor which the phase velocity is decreased relative to the velocity of the light in vacuum. i.e. Refractive index n =v (Speed of light in vacuum)/c (Speed of light in material) From this definition, the refractive index of a vacuum is equal to one while in practice air makes little difference to the refraction of light in vacuum. Since the velocity of light is reduced when it propagates through transparent gases, liquids and solids, the refractive index of these substances is always greater than one and the value of the absolute refractive index can be used assuming the incident light is in the air. So, we will take the exact value of refractive index of air into account because the refractive index values of the gases under investigations are closed to the refractive index of air.

2.1.

The Electrical Properties

According to Maxwell's theory I6.7] the dielectric constant is given by; £=n 2 (1) where n is the refractive index From the relations between the dielectric displacement, the polarization and the dielectric susceptibility Ke, we can get the relation between Ke and £ as the following; Ke=£-l (2) By Lorenz in Copenhagen l81 and Lorentz in Leydenl91 for a gram molecule of a substance M of density p the total volume is MI p and the molar refraction is given by; p=[(n 2 -l)/(n 2+2)](M/p) (3) the value (n 2 _1)/(n 2 +2) is known as the specific refractivity Asp of a dielectric llOl . Form the clasusius-Mosotti and Lorenz-Lorenzi 11.121 equations the molecular radius (r) can be calculated from the following equation; (M/p) Asp

= (411:/3) r 3 NA

where, NA is Avogadro's number

(4)

99

2.2.

The Transport Coefficients

The fonnula of the diffusion (D), the viscosity (T]) and the thermal conduction (x) can be obtained using the kinetic theory, the continuity equation and the rigorous theory for rigid sphere molecules'13 las follows; D = 2.6280 X 10 3 (T3JM) 1/2 / P r/ T] = 2.6693

X

10-5

(MT

)1/2/

cm2/sec

(J2 grnlcm sec

x= 1.9891 x 1O-4(TJM )112/(J2= (1514) (RIM) T] cal/grnlcm sec

(5)

(6) (7)

where, M is the molecular weight, R is the gas constant, T is the temperature and (J is the molecular diameter.

2.3.

Gas Mixtures

For any two gases with refractive indices nl and n2, the refractive index of its binary gas mixture is given by the following relation! 141; n = n] XI + n2 X 2 (8) where, XI and X 2 are the mole fractions per volume of the two gas components. The diffusion coefficient of a binary mixture is obtained from the following relation' 151;

(9) The viscosity and thermal conductivity of gas mixtures were driven by and Wassiljewa!16] as; (10)

where MI and M2 are the molecular weights of species I and 2. The thermal conductivity of binary mixtures l131 is given by; Xmix

3.

= 1989.1

X

10-7 [T(M I + M 2) / 2MIM211/2 /(J

(11 )

The Experimental Set Up

The experimental set up has six major sections are shown in Fig. (1) where; He-Ne laser as a light source (I), Gas sample's cell (II), temperature control system (III), pressure control system (IV), evacuation system (V) and set-up and performance of MZI. (VI).

100

..

Water inlet

VI

,............................... :............................................................. .I!?..~i!f.l!lU:n.p..l!mp. ........ :

············r············· Water feed house

Digital thermometer

Monochromater

Eye

Gas container II ------....

Pressure control

Figure I The experimental set up.

4.

Measurements

To measure the refractive index (n) of the gas under investigation, the experiment is arranged as shown in Figure 1. The gas's cell is evacuated by using the vacuum system to the pressure 2x 10-5 mbar where the gas's valve is closed then it is opened to transport the gas to the gas's cell. There are two cases of study, the first is the studying of the change of n with the temperature (T) at constant pressure n(T)p. Second is the studying of the refractive index (n) as a function of the pressure (P) at constant temperature n(Ph. The temperature of the gas under investigation is. changed by passing the heated water, around the gas's cell through the outer cylinder. The temperature is controlled at definite temperature (T ,) by controlling the rate of heated water flow. Here, the temperature of the gas becomes constant at T, and the gas's pressure is changed by using the micrometer screw. Then, the pressure is recorded using the Hg manometer to be PI and the change in the number of

101

interfering fringes ~N is detected by counting the fringes. Therefore, the relationship between ~N and ~P at constant temperature can be drawn as shown in figure2. From this Figure, the value of ~N/~P is obtained. Then, the refractive index can be computed using the following relation l17l ; n (P s)

= (")Jt )( MI / ~P )Ps + no

(12)

where, n(PJ is the refractive index at pressure Ps; A is the wave length of the laser light; t is the thickness of the cell; MI is the change in the number of fringes count; ~P is the change in the pressure and no is the refractive index of air. The pressure of the gas is increased to become P2 at the same temperature TI and the change in the fringes number is recorded at different gas pressures P3 , P 4, ... etc, This process is repeated so different values of n(Ph are obtained. The temperature of the gas is increased to a higher value T2 and the change of n as a function of P are plotted at the value of T 2. This step is repeated at different temperatures T 3, T 4 .... These relationships between nand P at constant temperatures, which denoted as n(Ph , are plotted, Also, the relations between n and T at constant P which denoted as n(T)p can be studied by plotting the relations between nand T at different constant values of P.

5.

Results and Discussion

The refractive indices of He, Ne and their binary mixture HeNe at temperature within the range 293 - 353 k and at pressure within the range 55 - 85 cmHg are measured. The accurate value of the refractive index for air is obtained firstly. Then, n of He, Ne and thier binary mixture HeNe gases are measured. Figures 3 represents the relations between nand T at constant values of P for He gas while Figure 4 gives the relations between nand P at constant values of T for Ne gas. In Figure 5, the variation of the measured refractive index values for HeNe gas mixture with pressure at temperature T=303 K is studied and compared with the calculated values using the mixing rules of equation (8) Some macroscopic parameters are calculated for the gases under investigation from the experimental data of the refractive indices such as permittivity E, dielectric susceptibility Ke, and the specific refractivity Asp using the relations (1-3), respectively. These three important macroscopic parameters give an information about the properties of a given dielectric gas in a large volume as shown in Figures 6-8, Figure 8 also shows the variation of dielectric constant of Helium-Neon gas mixture with pressure at temperature T=303 K and comparing it with the calculated values using Kraszewski expression 118 1, Since the three transport coefficients, the diffusion coefficient

102

D, the viscosity coefficient 11 and the thermal conductivity coefficient X, are inversely proportional to the square of the diameter of the molecule, the radius of the gas molecules under investigation are determined. Table I shows the molecular diameters of He and Ne gases compared with some literature values. Then, the transport parameters D, 11 and X, can be studied as a function of gas pressure P and gas temperature T as shown in Figures 9-11. Also, a comparisons between the evaluated values of the transport coefficients for helium and Neon gases and some literature values are presented in Table 2.

Table I A comparison between the evaluated values of molecular diameters for He and Ne gases and some literature values l3 , 17 1 Measured value in AU

Literature value in A 0

Ne T= 273K

P=I atm.

2,92

2.58 1151

He T= 293K

P=I atm

1.2

1.9 1191

Table 2 A comparisons between the evaluated values of the transport coefficients for He, Ne gases and some literature values I18 ,19,20.22.1 Measured values

1. Diffusion coefficient Viscosity

Thermal conductivity

He,

0,864 at T=323K P=latm 140 X 10.6 at T=293K P=latm 260,5x10 6 at T=293K P=latm

2. Ne

Literature values

3. He I20,21)21

0,507 at T=293K P=latm

0,851 at T=328K P=latm

312.9 x 10'" at T=293K P=latm

194,lxI0'" at T=290K P=latm

115,57 xIO'" at T=293K P=latm

360.36x I 0'" at T=296,7K P=latm

4.

Ne120,221 0.473 at T=293K P=latm 311.1xI0'" at T=290K P=latm 115.7IxI0·6 at T=296,7K P=latm

103 30

•

0

1=293 K

25 20 ~15 :E 13

"'~10

.'0 OJ

15 7:

0 -5 70

75

80

85

90

100

95

P cmHg

105

Figure 2 Number of shifted fringes of Helium gas vis the pressure change at 632.8 mm. wavelength and Pi =76 Cm.Hg.

1.00035

•

•

0

... 1.00030

1.00025

...t:.

•

0

• 0

0

/';.

...

•

•

0

t:.

...

•

•

t:.

...

0

•

•

0

•

1.00020

•

0

•

/';.

...

•

0

•

300

310

•

0

• 320

0

...

/';.

t:.

•

0

•

1.00015

1.0001 rt 290

•

0

330

0

• 340

P=B5 P=BO P=76 P=70 P=65 P=60 P=55

cmHg cmHg cmHg cmHg cmHg cmHg cmHg

• 0

... /';.

• 0

• 350 TK

Figure 3 Refractive Index of Helium vis temperature at constant pressure.

360

104

• 0

...

1.00040

t;.

• 0

•

1.00035 x

~'"

T=293 T=303 T=313 T=323 T=333 T=343 T=353

K K K K K K K

"> B 1.00030

~ a:

•

1.00025

0

...

50

...

0

... t;.

...

...

t;.

0

•

•

•

•

55

60

65

70

t;.

•

t;.

• 0

•

80

85

0

• • 0

•

•

...

...

•

t;.

•

0

0

0

0

0

i

1.00015

0

t;.

t;.

1.00020

•

•

•

•

•

•

0

75

P em. Hg

90

Figure 4 Refractive Index of Neon vis pressure at constant temperature.

UXXJ36

• re-~c-'j 0

taXX34

re-~exp

I

1.CXXJ32

t

0 0

•

OOJ3O

'" > g1.00:J28 il

0

'"

1.00:J26 1.00024

1.00:J22

0

•

1.00:J20

50

55

60

65

70

75

00

85

90

P ITessure clnHg

Figure 5 Refractive index of helim-Neongas mixture (exp) and Helim-Neon calculated by equation (1.70) vis pressure at temperature T=303 K.

105 0..0.0.0.8

0.0.007

g :0 "a

~

0..0.0.0.6

0..0.0.0.5

u

0

• 0

0;

'" t'1

•

•

'"

0

0

t'1

'" 0

•

t'1

•

0

•

290.

30.0.

310.

•

320.

'" •

0

•

0

'" •

t'1

0

0..0.0.0.3

•

0

'"

t'1

P=85vmHg P=80cmHg P=76cmHg P=70cmHg P=65 cmHg P=60 cmHg P=55cmHg

•

0

'" •

•

•

•

0

t'1

0

0..0.0.0.4

•

0

t'1

0

•

•

'" •

•

•

'5 :6

is

•

330.

t'1

0

340.

• 350.

360. TK

Figure 6 Dielectric susceptibility of Helium vis temperature at constant pressure.

0.00028

• 0

0..00026

... t>.

•

0..00024

::;,

0

•

":; 0..00022 t)

~1) 0..00020

T= 2ffi T=303 T=313 T= 323 T= 333 T=343 T=353

.....

.~

'u

0..00018

•

1)

0-

til

;-

0..00016 0..00014

50

•

0

...

0

...

t>.

0

...

...

t>.

...

t>.

•

•

t>.

• 0

0

•

65

70.

• 0

• •

55

60

•

0..00010.

•

•

0

0 t>.

0..00012

•

•

• 0

• 0

...

...

t>.

t>.

•

• 0

• •

0

•

0

0

75

80

85 Pall;g

Figure 7 Specific refractivity of Neon vis pressure at constant temperature.

90

106

•

(HeNe) expo (HeNe) cal.

0

I

1.00070

c

0

0

1.00065

~ c 0

<.)

•

0

•

1.00060

•

<.)

·c ti V 1.00055

0

.,

0

•

0

Q,I

1.00050

0 1.00045

1.00040

•

•

0

•

+---..,---.,-----.----r---.---.---.------j 55 60 70 75 90 65 80 85

50

P pressure cmHg Figure 8 Dielectric constant of helim-Neon gas mixture (exp) and helim-Neon calculated by

"Kraszewskiexpression" vis pressure at temperature T=303 K.

1.6

•

0

N

.,c..i

1.4

E '-'

1.2

...

/).

•

~

".,

'u b:., 0

0

•

P=85 P=80 P=76 P= 70 P=65 P=60 P=55

cmHg cmHg cmHg cmHg cmHg cmHg cmHg

•

.~

• •

0

/).

/).

~

•

is

ci

~

0.6

0

•

/).

~

~

•

...0

...0

/).

...0

•

•

•

•

• /).

/).

•

/).

0

0

0

0

•

0

•

:::: 0.8

it::

•

•

•

1.0

U c

•

0.4 290

300

310

320

330

340

350

TK 360

Figure 9 Diffusion coefficient of Helium vis temperature at constant pressure.

107 0.00060

0.00055

0
•

•

0.00050

0

•

{),.

{),.

0.00045

T

'Vi 0

• 0

•

T

0 0.00040

•

t)

'" > ..c:

T {),.

{),.

bJ)

C

T=293K T=303K T = 313 K T = 323 K T=333K T=343K T = 353 K

0

0

Ul

S -'2 S

•

•

0

•

0.00035

T

0

•

• 0

•

•

• •

0

•

0

• • 0

{),.

•

{),.

0

T

•

0

• 0

{),.

T

{),.

T T

•

0.00030

0

•

0

•

0.00025 50

55

60

65

70

75

80

85

PcmHg

90

Figure 10 Viscosity of Neon vis pressure at constant temperature.

0.00040

• 0

oj
Ul bJ)

•

0.00035

"0

E

{),.

~ ~

u

0.00030

T

0

:~

0

"0

•

u::l

"

0.00025

0

u

•

• 0

• {),.

... 0

•

~

E ....
T =293 T=303 T =313 T =323 T =333 T =343 T =353

0 T

{),.

• 0

• b.

... 0

•

• 0

•

• •

0

•

0

•

{),.

...

{),.

...

0

•

0

•

0.00020

u

0

•

{),.

... 0

•

•

K K K K I( K K

• 0

•

{),.

... 0

•

0.00015 50

55

60

65

70

75

80

85

P cmHg

90

Figure 11 Thermal conductivity of Helium-Neon gas mixture vis pressure at constant temperature.

108

6.

Conclusion

1- The MZI and the gas flow system (GFS) have been combined and used successfully to determine the refractive indices (Rrs) of some gases and their binary mixtures (He, Ne, HeNe) as a function of pressure, n(Ph, and temperature n(T)p.

2- The related physical parameters (optical permittivity, dielectric susceptibility, and specific refractivity have been efficiently studied as a function of both pressure and temperature. From these studies, the physical parameters are increased with increasing of the pressure at constant pressure, while these parameters are decreased with increasing of the temperature at constant pressure. 3- For the binary mixture HeNe gas, good agreement have been achieved between the experimental results and the calculated one using some mixing rules. 4- The dependence of the diffusion coefficient and viscosity on the temperatures and pressures have been studied perfectly for the gases under investigations. The results of the diffusion coefficient give good agreement with the ultra kinetic theory of gases. 5-A good agreements have been obtained between our measured values and the other literatures values.

7. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [ 13] [14] [15]

References A.J.T. Holmes, and J.R. Conzens, J. Phys. D: Appl. Phys., 8,4004 (1975). Y.P. Kathuria, 1. Opt. 22 [49-15], (1991). Carolyn R. Mercer, NASA Lewis Research Center, E- 11213, (1998). Y. Chen, S.J. Kirkpoitrick, S.A. Prahl, Proceedings of the Oregon Academy of Science, 38,44, (2002). Valentin Korman et aI., 1. Opt. A: Pure Appl. Opt. 6781-786, (2004). C.D. George, P.M. Thomas and C.D. Joseph, "Physical and Theoretical Chemistry" S. Chandal Co. (1970). D.1. Schlueter and E.R. Peck, J. Opt. Soc. Am., 48, 313, (1957). Lorenz: Wied. Ann., 11, 70, (1880). Lorentz, H.A.: Wied. Ann., 9, 641, (1880). August Chelkouski "Dielectric Physics" PWN. Polish Scientific Publishers, (1980). R. Clausius, "Mechanishe Wormetheorie" 2 (Braunschweig, 2 nd ed., P62, (1979). O.F. Mosotti, Mem. Soi. Modena, 14,49, (1950). Joseph O. Hirschfelder, Chari as F. Curtiss, R. Byron Bird "Molecular Theory of gases and liquids" copyright, USA. (1954). http://www.nv.cc.va.us/home/mbobriklhybridrefract.htmJ Hirschfelder, Joseph 0., Curtiss, Charles F., and Bird, R. Byron: Molecular Theory of gases and liquids. John Wiley & Sons, Inc., p531, (1954).

109

[16] Wossiljewa, A.: Heat Conduction in Gaseous Mixtures. Phsik Zs., Vol. 5, pp. 737-742, (1904). [17] Yuam Shi, Man Wli-Ning, Yu Jin and Gao Jin-Yue, Chinese Phys., Lett., 18, 364, (2000). [18] A. Kraszewski, S. Kulinski, M. Matuszewski, J. Appl. Phys. 47(4) 12751277, (1976). [19] www.cirris.com/testingiaircraftlhelium.pdf [20] Saxena S.c., Mason E.A., Molec. Phys. 2(4), 379, (1959). [21] R.c. West, M.G. Astle (Eds), CRC. Handbook of Chemistry and Physics, (1979). [22] Winn E.B., Phys. Rev. 80(6), 1024, (1950).

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1-4. Posters

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ANALYTICAL STUDIES OF LASER BEAM PROPAGATION THROUGH THE ATMOSPHERE

M. I. EL-SAFTAWY, AFAFM. ABD EL-HAMEED and N.SH. KHALIFA National Research Institute of Astronomy and Geophysics, Helwan, Cairo, Egypt

The present work deals with the studying of the laser beam propagation through the earth's atmosphere. The linear mechanism of laser atmospheric interactions is taken in our consideration. Under this assumption, the analytical model describing the atmospheric attenuation of the laser beam power during a long rang propagation is studied. The laser power at the surface of the satellite and that reflected from the satellite's retro reflectors to the ground telescopes at the station are discussed in details. Simulation study is applied for the second harmonic Nd-YAG laser. The obtained results are interpreted for the data measured by Helwan Satellite Laser Ranging (SLR) station for various satellite configurations at different atmospheric conditions. Keywords: Laser propagation, atmospheric effects, Beam spreading; Laser power attenuation, Satellite Laser Ranging and satellite laser reflector array

1. Introduction The atmosphere is a blanket of air of thickness over 400 miles surrounding the Earth. This envelope of gases changes from the ground up and consists of four distinct layers each of which has its own characteristics (e.g. density, temperature, constituents, ... ect). Atmospheric components and weather conditions affects the laser beam propagation. Small-scale dynamic changes of the index of refraction of the atmosphere result in beam deformation (e.g. beam wander, beam spreading and distortion of the wave front or scintillation). Moreover, the laser power is attenuated by the absorption and scattering of laser photons by different atmospheric constituents which can be classified into two classes; aerosols and gaseous molecules. Two different mechanisms of atmospheric interactions illustrate the laser power attenuation; linear and nonlinear mechanism. Linear interactions produce a linear decrease in the laser beam intensity and it can be considered as the dominant atmospheric effect l - 13 . Moreover for a moderate laser peak power, nearly about 4 GW, there is no significant contribution of non-linear effect to the overall beam propagation l4 .

113

114

The purpose of this paper is to point out the power attenuation of the laser beam used in satellite laser ranging stations under the mechanism of linear atmospheric interactions. In addition, simulated studies for laser power received by two satellites' retro-reflector array with different configurations will be performed.

2. Modeling of Atmospheric Effects The density of the Earth's atmosphere decreases from ground up. So, the attenuation of the laser power can't be considered as constant over the whole atmosphere. The power attenuation is described by the improved version of Lambert-Beer's law which deals the attenuation coefficient as a function of the distance traveled by the laser beam through its propagation and integrates attenuation coefficient over the path distance l5 . The laser intensity of a laser beam, sa (R ) , received at range R may be describes as: R

sa (R)

=S (0)

-f e

u(R)dR

0

(l.a)

Where the suffix "a" refers to the atmospheric attenuation intensity. The total attenuation coefficient, (J'(R), is the contributions of the absorption and scattering of laser photons by different aerosols and gaseous molecules and can be described as: (J'( R )

= (J':~ ( R )

Where, (J':~ (R),

+ (J'j:~ ( R ) + (J':;;; ( R ) + (J':;~l ( R ) ,

0':;;; (R),

(l.b)

O'~~ (R) and O':;~l (R) are the attenuation

coefficients at distance, R, due to aerosols scattering, aerosols absorption, molecular scattering and molecular absorption respectively.

2.1 Power Attenuation of Second Harmonic Nd-Yag For beams of wave length - 532 nm, the contribution of absorption of both aerosol and molecules absorption coefficient to the total attenuation coefficient can be neglected 2. 6.16-19,33. Therefore, the total attenuation coefficient can be reduced to the form:

(2)

115

The lower layers of the atmosphere are almost the densest pareo. So, the power attenuation through the lower atmospheric layers are considered to be of dominate effect over the whole atmosphere. 2.1.1 The Molecular Scattering Coefficient (j~~ (R)

Through the lower atmosphere, the density of molecules varies exponentially with height as given by the following relation 5, 21

N ( h) = N (0) e( -h/ho ! ,

(3)

Where N(h) is the density of atmospheric molecules at height h, N(O) is the density at the sea level (h o - 7 km). Consequently, the molecular scattering coefficient varies with height and can be given by5, 21 (jmol ( scat

h)

= (jmol ( 0) ( -h/h scat e

o )

(4)

,

Where (j~:: (0) is the molecular scattering coefficient at the sea level. However, the laser beam is fired at some angle, ¢, known as the elevation angle, which related to the height h through the following simple geometrical relationship shown in the figure below; as:

h =R sin¢.

(5)

~

h~ Beam Range and Height

Laser source

116

Substituting from Eq. (5) into Eq. (4), the extinction coefficient due to molecular scattering over range R becomes: mo1 (R) = a mo1 (0) e(-R sint/J/h ascat scat

(6)

o ) •

2.1.2 The Aerosols Scattering Coefficienta:~ (R) The aerosols scattering coefficient has a great value at the lower atmosphere and strongly reduced above 21 . For homogenous atmosphere, the

"".1 Km -1 for typical clear air conditions, "" 1 Km-1, in haze conditions, "" 10 Km- 1 for fog conditions (with a visibility of roughly 4 Ian), and"" 397 Km- 1 for a dense fog aerosols scattering coefficient, a:::t , has empirical values

with a visibility of lO meters l • 18.22.24. Back to Eq. (2), the total attenuation coefficient will be: a(R)

mol (0) e(-Rsint/J/h = a scat

o )

+aare (R) scat

(7)

.

Substituting into Eq. (1.1), the laser intensity, Sa (R) , received at range R is given by: (8)

2.1.3 Propagation through Vacuum For long range space laser application (e.g. satellite laser ranging), the beam leaves the atmosphere and propagates through vacuum. Virtually there is no matter to absorb or scatter the laser photons and the beam will spread as follow 5

s,.(R)=

p~

:rR

2

e

(9.a)

With (9.b)

Where the suffix "s" refers to beam spread through vacuum, Po is power at the laser source,

e is the beam divergence, Dl is the diameter of the laser

transmitter, and

A is the laser wavelength.

117

Atmospheric effects and beam spread result in an overall attenuation of the beam strength. Consequently, the intensity of a laser beam fired through the Earth's atmosphere from a ground station by an angle ¢ to a satellite at rang R will be:

sl(R)~

P

~

_[[~~ (O)ho ][l-fu 2

e

e

sin(¢)

(_ R sin(¢))]+~, ]

P

ho

.em

(10)

7lR Satellite laser ranging technology make use of lasers to measure ranges from ground stations to satellites equipped with specially designed reflectors to return the incoming laser pulse back to the transmitting site. The laser reflecting array consists of number of corner cubes made of highly homogeneous fused silica with external coating of reflectivity specified to exceed 75% at 532 Angstrom 25 . Each corner cube acts as a separate source, thus an interference pattern is produced in the returned beam. This pattern will move across the ground station as the satellite moves along its orbit26 . Therefore, the returned laser intensity depends on the shape and thermo-optical properties of the satellite laser array. So, the intensity received at the ground station will be: (11)

where p is the reflectivity of each laser reflector, Dll is the diameter of each reflector and n is its number. The parameter X which represents the ratio of the area of the laser retro-reflector array to the total satellite area differs from one satellite to another according to the shape of the laser array.

3. Numerical Simulation of the Atmospheric Beam Propagation

Propagation of the second harmonic Nd-YAG laser, used for satellite laser ranging at Helwan station, has been simulated. The intensity of the NdYAG laser at two satellite laser reflector array of different shapes is estimated. The parameters of laser system are described in table 1 and the system setup is illustrated in figure 1. The following simplifying assumptions are adapted:

118

Table 1. The parameters of the used laser system

Nd-YAG Semi train laser

1. 2.

.53)J.m

Energy

80mj

Pulse Width

17 Psec

Repetition Rate

Up to 5 Hz

Beam Divergence

0.1 - 1 mrad

Receiver Diameter

40 em

The lower atmosphere is the first 50 Jan of the Earth's atmosphere 2o . The inscribed circle of each reflecting corner cube has a diameter

Dll 3.

Wavelength

The

= 27 X 10-3 m 27. molecular

scattering

weather coefficient a:~

coefficient

at

the

sea

level

for

(O"s:~(0)=1.7xlO-5m-I)28 while for clear

A=532nmis

condition,

the

aerosols

scattering

=.0001 m -I.

The accuracy of range measurements by Helwan SLR station is few centimeters (- ±4cm intensity.

), with an error don't exceed 10-4 for the laser

119

CCDCom,,,

Figure 1. Setup of Satellite Laser Ranging System Used at Helwan SLR Station

3.1 Laser Intensity at Symmetric Satellite Laser Array The Experimental Geodetic Satellite (EGS) known as 2

AJISA! with

CaSPAR ID 8606101 has a spherical shape with 215x 10- m diameter29 • It carries 120 laser retro reflector assemblies having 1436 corner cube reflector3o • The laser retro-reflectors distributed symmetrically over the satellite surface, so the parameter X = .5. By applying the model for one satellite path in 2004, November, 11 from 17.3966111 to 17.5748334 universal time, the relations between the laser intensity in units of watt / m and the satellite range in units of meter m during the time of observation are plotted in the following figures. Figure 2 illustrates the behavior of the laser intensity slat the satellite surface with respect to the satellite range. It is found that as the satellite range decreases, the laser intensity S 1 increases. Similar behavior for the laser intensity S 2 received at the ground station is illustrated in figure 3.

120

-7 ~-R

2600000

2400000

I

2200000

350000

300000

!!?

.:;t 250000

g> '"

~

::>

2000000

en

~

'"

OJ

a::

200000 ::

3

1800000

-Y

150000

1600000 17.38 17.40 17.42 17.44 17.46 17.48 17.50 17.52 17.54 17.56 17.58

Time of laser shots

Figure 2. Relation between the measured range and the estimated laser intensity at the satellite surface.

~-R

2600000

220000 200000

2400000

180000

2200000

140000 !!? .:;t

160000

I 'g>" a:: '"

~ ::>

120000 ~ 2000000 100000

~ OJ

80000

1800000

~ ~ ~

60000 40000

1600000

17.38 17.40 17.42 17.44 17.46 17.48 17.50 17. 52 17.54 17.56 17.58

Time of laser shots

Figure 3. Relation between the measured range and the estimated laser intensity recei ved at the ground station

Moreover, the relations between the laser intensity in units of

watt / m and elevation angle measured in degrees during the time of observation are plotted in figure 4. The figure illustrates the behavior of the laser intensity slat the satellite surface with respect to the satellite elevation angle. It is found that as the satellite elevation angle increases, the laser intensity S 1

121

increases too. Similar behavior for the laser intensity station is also shown in figure 5.

S2

received at the ground

65 ~¢

Q)

350000

- - s1

60

~

55

~

...'"

50

~

45

'"

40

'? OJ

35

200000 ::

300000

Cl

c:

.2

n;

III

250000

~ III ~

3

>

~

ro

:J

c:

OJ

or

30

'"

150000 25 17.38 17.40 17.42 17.44 17.46 17.46 17.50 17.52 17.54 17.56 17.56

Time of laser shots

Figure 4. Relation between the measured elevation angle and the estimated laser intensity at the satellite surface

450000 65 60

Q) ~

55

OJ

'" :s ....

50

~

45

c:

c:

40

0

~

35

>

~ Ql

--S2

30

f I~

!

I

400000 350000

s·

\

p

Cl
f

~-¢

1"

300000

"\

ro

:J

!!?

250000

\

-<

'"'"

200000,? OJ

\..

\

150000 ::

3

\.

100000 50000

25 17.38 17.40 17.42 17.44 17.46 17.48 17.50 17.52 17.54 17.56 17.58

Time of laser shots

Figure 5. Relation between the measures elevation angle and the estimated laser intensity received at the ground station

122

3.2 Laser Intensity at Annulus Satellite Laser Array The Ocean Topography Experiment! Poseidon rrusslOn known as Topex/Poseidon spacecraft with COSPAR ID 9205201 is an active satellite of

.019cm 2 / g to

complex shape qf area to mass ratio varies from

.140cm 2 / g and total mass of 2500 kg3 !. Its retro-reflector array is an annulus ring of 150 cm diameter comprised of 192 corner cubes and the parameter

X = .0505102

27.

Applying our model for one satellite path as an example in 2005, August, 8 from 17.4848334 to 17 .6040556 universal time, the relations between the laser intensity and the satellite range during the time of observation are plotted and discussed as follows: Figure 6 illustrates the behavior of the laser intensity s! at the satellite surface with respect to the satellite range. The figure shows that, as the satellite range decreases, the laser intensity s! increases. Similar behavior for the laser intensity

S2

received at the ground station is illustrated in figure 7.

2400000

---R

--S1 2300000

~I

0

2200000

.s

1')

I

0> C

~

300000 280000 ~ (1)

260000

2100000

~

Q)

320000

:::J ~.

-<

240000 ~

2000000

220000 ~ 1900000 200000

~

~

1800000

180000

1700000

160000 17.48

17.50

17.52

17.54

17.56

17.58

17.60

17.62

Time of laser shots

Figure 6. Relation between the measured range and the estimated laser intensity at the satellite surface

123

2400000 2300000

l e

2200000

g

350000

-R J --82 "

2100000

I

300000

5" 250000

<J)

IX

'"c IX '"

C)

g ~

200000

2000000

~

~ III

1900000

150000 ;::::

3

--Y

1800000

100000

1700000 +--.---r--.-~r--r--'---r-~--.---r--r--'---r-~---r50000

17.48

17.50

17.52

17.54

17.56

17.58

17.60

17.62

Time of laser shots

Figure 7. Relation between the measured range and the estimated laser intensity recei ved at the ground station

The variations of the laser intensities s 1 and s 2 with the elevation angle ¢ are shown and plotted in Figures 8 and 9 respectively. The figures clarify the same behavior as that in the case of symmetric array but with different values depending on the array construction. 50 .---r-~---r--r--'--'---r-~--,---r--r--'---r-~---r340000 - - 1 - - rP --81

48 46

320000

44

300000

Q) ~

42

280000 5"

0)

CD ::J

'"

40

""-

38

~

~

..!E

260000

<J)

C)

36

240000 ~

'"c

34

220000 ~

~

32

c 0

> ..!E

30

Q)

28

200000

§'

--Y 180000

26

160000

24 17.48

17.50

17.52

17.54

17.56

17.58

17.60

17.62

Time of laser shots

Figure 8. Relation between the elevation angle and the estimated laser intensity at the satellite surface

124 50 48

-"""'-¢

46

--82

Q) 44

e

0) Q)

~

....

~

350000

300000

42

::J

40

250000

38

~

en ~

~

0)

36

CO

34

~

150000 ~

c c 0

32

>

30

Q)

28

~ ~

200000

\

26 24

100000

'" -=-~

+--'-_'--'-r-_-.-r-_-.-.-_-.-r-~50000

17.48

17.50

17.52

17.54

17.56

17.58

17.60

17.62

Time of laser shots

Figure 9. Relation between the elevation angle and the estimated laser intensity recei ved at the ground station

4. Conclusion

For Helwan SLR system, the analytical model represents the laser intensity reaching to the satellite surface that returned back to the ground telescope in the station. The obtained results show the dependence of laser intensity on the laser system and satellite range. Moreover, the returned intensity depends on various parameters of satellite's configuration; the number of corner cubes and the shape of the retro-reflector array which are differ from one satellite to another.

References 1.

2. 3.

J.C. Ricklin., F.D. HammeIS.,Eaton., and S.L. Lachinova., Springer,2005. P.B.Harboe and J.R Souza. journal of microwaves and optoelectronics, 3:4, (2004) A.,Akbulut Efe, A.M.,Ceylan F., Ari Z,Telatar, H Ilk Gokhan and S,Tugac Ankara University Scientific Research Projects, Project No: 2001-00-00-006.

125

4.

5. 6. 7. S. 9. 10. 11. 12. 13. 14. 15. 16. 17. IS. 19. 20. 21. 22. 23. 24. 25.

26.

27.

I. Kim , R Stieger, 1.A Koontz., C. Moursund., M. Barclay , P. Adhikari, 1. Schuster, E. Korevaar, R Ruigrok., and C. DeCusatis, Opt. Eng. 37(12),3143-4155 (1998). P.E Nielsen., Library of Congress Cataloging in Publication Data (1994). P.E Grotzinger., Laser wireless Inc , (2005). A.S. Bashkin, V.N.,Beznozdrev, N.A. Pieogog Quantum electronics 33(1) 31-36 , (2003). Accetta, Handbook, volume 2: Atmospheric Propagation of Radiation, (1993) H. Weichel., SPIE, Bellingham W A, (1990). W.E. Martin and RJ Winfield., Applied Optics, 27, 3, (1988). V.E. Zuev., Consultants Bureau (Plenum), New York, (1982). FG Gebhardt .,AppI.Opt. 15,1479,(1976) W.E.K. Middleton., U. of Toronto Press, Toronto, 1952. J.Kasparian, Private communications, (2005). R M.Goody and. Y. L,Yung "Atmospheric radiation: theoretical base",2nd ed. Oxford University Press, (1989). L.G Stephens., Oxford Universitt press, Inc, (1994). C.FBohren and Huffman D.R , Wiley- interscience publication,1983. I. Kim, E. Korevaar and B. McArthur, Proceeding of SPIE, 4214, optical wireless communications Ill, (2001). G. Li., G. Chadha, and C.R Philbrick, Aerosol Science and Technology, (2000). E Danielson.,and J.,AbramsLevin E.,"Meteorology", second edition, McGraw-Hili Companies (2003). F Reif, Fundamentals of Statistical and Thermal Physics, New York: MCGraw-Hill, (1965). M.1. El-Saftawy and M Ibrahim., Nriag Journal of Astronomy and Astrophysics, special Issue, (2004) G.A. Miner and P.D. Babb., NASA technical memorandum 4420, (1993). E. J McCartney., Optics of the Atmosphere, J. Wiley & Sons, New York, (1976). http://209 .S5.165.104/search?g=cache:dbjAistK3M4J :cddis.nasa.gov/ lw 14/docs/papers/tar 1a tum. pdf+satellite+laser+retroreflector+array+description&hl=en&ct=clnk&cd=2 RG. Sellar., RL. Phillips., L.c. Andrews., c.Y. Hopen, D.M Shannon., J.J. Huddle, A. Marcos., J. Bachelor, and K. Van., Shuttle Small Payloads Project Symposium's presentations, (1999). http://ilrs.gsfc.nasa.gov/satellite missions/list of satellites/topexlinde x.html

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28. O.F.Prilutsky, and M.N. Fomenkova., Science & Global Security , 2, 7, (1990). 29. http://www.nasda.go.jp/projects/sat/egs/index e.html 30. M. Sasaki, and H. Hashimoto, "Launch and Observation of the Experimental Geodetic Satellite of Japan', IEEE Transactions on Geoscience and Remote Sensing, 25:5, Sept. (1987) . 31. P. G.Antreasian, and G. W Rosborough,. "Prediction of radiant energy forces on the OPEXIPOSEIDON spacecraft", 1. Spacecraft and Rockets, 29(1), 81-90, (1992).

II - Laser Applications in Engineering 11-1. Invited Lectures

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LASER TECHNIQUES IN CONSERVATION OF ARTWORKS:

PROBLEMS AND BREAKTHROUGHS RENZO SALIMBENI and SAL V ATORE SIANO

Institute of Applied Physics "Nello Carrara" - CNR, Via Madonna del Piano n.10, 50019 Sesto F.no (Fl), Italy

After more than thirty years since the first experiment in Venice, only in the last decade laser techniques have been widely recognised as one of the most important innovation introduced in the conservation of artworks for diagnostics, restoration and monitoring aims. Especially the use of laser ablation for the delicate phase of cleaning has been debated for many years, because of the problems encountered in finding an appropriate setting of the laser parameters. Many experimentations carried out on stone, metals and pigments put in evidence unacceptable side effects such as discoloration and yellowing after the treatment, or scarce cleaning productivity in respect of other techniques. Many research projects organised at European level have contributed to find breakthroughs in laser techniques that could avoid such problems. The choices of specific laser parameters better suited for cleaning of stone, metals and pigments are described. A series of validation case studies is reported.

1. Introduction

The remnants of past civilizations are an important part of the historical and cultural identity of the population of each country. This is certainly true for countries where their history has left worldwide renowned cultural heritage, as in Mesopotamia, Egypt, China, Europe, India, Centre America, hosting very ancient monuments dated thousands years ago. In many archaeological sites or in the underground of cities a stratification of several historical layers may be found, revealing objects, tools and artworks. The situation of conservation of monuments, historical buildings and museum collections, spread throughout the entire world shows today a number of risks of natural origin, (earthquakes, floods, fires, wind, sand) and other risks depending on the human factor (intentional damage, war destructions, anthropogenic deterioration, air pollution, wrong or absent regulations). The uniqueness of each piece of this treasury justifies the need of the most developed means in order to preserve the material itself against the many sources of deterioration. Because of this, the conservation community has always explored the potential of newly developed science and technology for solving the problems they are everyday facing. Since the opening of a modern meaning of restoration, chemistry has been mostly involved, providing reactants, poultices for consolidation and cleaning, coatings for protection. Physics as discipline has also given very important contributions as microscopy, optical and X-ray investigations. Laser and opto-electronic techniques came in about thirty years ago [1], giving immediately very promising diagnostic and restoration procedures. The

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evolution and spread of laser techniques took necessarily many years, because of many factors: first of all the lack of scientific background in the conservation institutions, and secondly the need for more developed laser instrumentation. Nevertheless restoration interventions employing Nd:YAG laser cleaning took place during the years 80's in Italy, and along the early 90's in France and in the United Kingdom. In the 90's also in Greece and in Germany investigations using Excimer lasers began. For many years the experimentation of laser cleaning techniques remained limited because of problems that did not allow a faithful acceptance by the conservators community. For this reason many projects tried to find correct solutions regarding the application of lasers for cultural heritage preservation. The aim of this paper is to present a selection of studies that could demonstrate to provide real breakthroughs for the specific laser cleaning problems previously observed on stone, metals and pigments. The conservation studies here reported are necessarily examples of problems arising in European sites, but considering the flexibility of most of the laser technologies here presented, their value is of pertinence also for the complex variety of problems that can be found under very different environmental situations in every part of the world .

2. Laser Cleaning of Encrustation on Stone The physical process involved is laser ablation of inorganic (sometimes also organic) layers composing the deterioration crust. In facts the large variety of stone materials typically employed in artworks, monuments and historical buildings have the common problem of being under the complex process of interaction with the environment [2]. Outdoor monuments and also collections of artworks hosts in galleries experience every day the result of chemical and physical deterioration processes. Stones exposed to urban environments develop on the surface the typical sulphation process, with calcium carbonate turned in gypsum, carbon particles deposits, finally leading to a weakening of the material stability and in the worst case to a loss of historical materials or of their artistic value.

Figure I. Ultrathin section of degraded marble, showing the black encrustation, a patina layer and calcite crystals .

In many cases a restoration intervention encounters most of the problems being due to previous interventions, made out with the state of the art technology of some tens years ago. Generally speaking we may say that any invasive addition of

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extraneous material could have a negative exit after some time, because of the difficulty to foresee their behaviour. Somehow the restoration intervention becomes often an extraordinary need, urged by serious conservation problems. An important contribution would certainly be to innovate the intervention with a methodology providing a minimal invasive action for the degraded material removal, and also the possibility to make reversible the addition of extraneous materials. Laser cleaning is a good candidate for this task. The most important characteristics observed since the beginning have been: Laser cleaning is essentially a surface treatment, where only a thin layer limited to a few microns or less than a micron is directly involved by absorption of light, while chemical methods usually perfuse with solvents internal layers without control; Accurate control of the removal depth, due to the very progressive action of the laser, removing pulse after pulse the encrustation; The cleaning process terminates by itself whenever the encrustation is totally removed also if the substrate is accidentally exposed to the laser radiation. The physical basis for such characteristics is the "optical contrast" between the dark encrustation and the light colour stone.

Laser beam (F, A)

Figure. 2. Schematic view of the two materials M, (crust) over M2 (stone)

If the optical absorption coefficient UI of MI is higher than the absorption coefficient U2 of M 2 , then the extinction length 01 of the laser radiation in the material MI will be shorter than the extinction length 02 in the material M 2.

Consequently the energy amount needed for the ablation of the crust will be lower than the one needed for ablation of the stone.

132 mabl [lJg/pulse] dabl [lJm/pulse]

Operative Ifluence

Figure. 3. Typical ablation curves for cleaning cases.

Figure 3 reports the typical differentiation observed between the ablation curve of the crust (M 1) and the ablation curve of the stone substrate (M2)' The fluence threshold for the crust is significantly lower than the one of the stone. A suitable choice of the operative fluence will determine a selectivity of the ablation effects and the "self-termination" effect, i.e. the absence of effects if the stone receives a laser shot, because such operative fluence is not sufficient to ablate the stone. Because the extinction length in the typical sulphation crust of Nd:YAG laser wavelength may be in the order of a few microns or less, each laser pulse at the operative fluence may remove progressively thin layers of the crust, achieving the expected good control of the cleaning process. Furthermore the focussability of laser beams in small spots, where the conditions for ablation are reached, makes the cleaning very precise also spatially, allowing the restorer to follow easily the morphology of the artwork and aiming the beam where is needed. In conclusion the expectations outcoming from the initial experimentations were promising an almost ideal tool to remove progressively and selectively the deteriorated layers, without any effect on the underlying historical material in good conservation state. Unfortunately many studies and experimentations were still needed to achieve the full potential of laser cleaning for stone.

133 3. Problems Associated with Cleaning of Stone Nd:YAG lasers operating in Q-switch mode have been employed since the beginning, after the first pioneering test by J. Asmus [1] in Venice in the 1972, using ruby lasers. The interest in laser cleaning started again in the '90s in France [3] with the restoration of many churches, employing Q-switch Nd:Y AG lasers for the cleaning of portals of cathedrals in Amiens, Mantes-La JoIie, Paris, Chartres, Saint Denis etc. Another group was studying laser cleaning of artefacts in Liverpool [4] still using Q-switch Nd:YAG lasers, while in Crete [5] also excimer laser begun to be considered for icons and paintings, and in Germany [6] some groups considered the problems of historical glass as candidates for excimer laser cleaning. In Vienna the St. .Stephan cathedral [7] was another important step in the validation of Q-switch Nd:YAG laser cleaning, and in Italy several trials were carried out back in the '70s and in the '80s in Venice, Padua, Cremona [8]. Many of these experimentation put in evidence a series of problems that were discouraging or unacceptable by conservators: Critical fluence range, with risk of excessive cleaning when the fluence rises of a few 10%; Surface yellowing after laser cleaning of the stone encrustations; Unpractical utilisation of the laser instrument in the dusty and weathered condition on the scaffoldings; Low productivity in respect of sand-blasting or pressurised water spray; Discoloration of pigments present as polychromes under the crusts. In facts the typical operative fluence determined by many independent experiments was relatively narrow for the Q-switch Nd:YAG laser, ranging between the fluence threshold set at 0,5-0,8 J/cm2 and the saturation level for plasma formation set at 1,2-1,5 J/cm2 . In other words a fluctuation of the fluence along the spot area of 50% could easily provoke no effect or excessive effect. The intensity fringes typical of Nd:Y AG beams were often marked on the crust at each shot, as evidence of these intensity dependence. The development of high power laser systems, capable to reach 100 W average power, was aimed to rise the productivity in terms of m2/hour, while smaller laser systems could barely reach a fraction of unit area, but not even this achievement could spread the use of laser in professional restoration. The main source of criticism was anyway the effect of yellowing observed in France on the stone after the laser cleaning, because this yellowing needed a further treatment to be eliminated, and finally it turned out that French conservators didn't use anymore lasers after these negative evaluations.

4. Proposal of Other Laser Regimes for Stone Cleaning A critical analysis of the photophysical effects associated with Q-Switch laser cleaning brought our group in Florence to propose free-running mode Nd:YAG lasers for experimental cleaning. The motivation to leave Q-Switch was due to the intense mechanical forces associated with the plasma generation and its expansion dynamics. We could demonstrate that the blast wave following to Q-switch laser cleaning was able to couple significant pressure to the substrate. Free-running mode laser would have on the other hand very long pulse widths, in the order of hundreds of microsecond up to millisecond, and consequently

134 photothermal effects could take place, inducing a large extent of heat affected zone. So, in conclusion, a Short Free Running Nd:YAG laser (SFR) was developed and tested, with a typical duration of a some tens of microseconds [9]. According to the dependence of the affected zone with square root of time,

td l12 , where D is the heat diffusivity. For stone materials Ztherm may be in the order of a micron if tL is in the order of tens of microseconds, consequently there are negligible thermal effects for the case of stone cleaning in this regime. Ztherm=(D

100

'i' VI

"S

~

OB SFR 50 iJsec

80

a

60

~

40

XB SFR 80 iJs

.6.

LlB SFR 90 iJS

.6.

c

•

• Column SFR 120 iJs

.6.

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~ ~

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Fluence (Jlcnt] Figure 4. Ablation rates with SFR laser for cleaning of samples (8) and of a tortile column made of encrusted marble. at various pulsewidths

The ablation process in the microsecond regime was found to be more expensive in terms of energy expenditure, because the fluence threshold has also square root dependence with time due to the heat conduction effect. The material removal takes place as a slow vaporisation, which of course is favoured if the material is wet by water. In the wet case the typical threshold is set at 3-4 J/cm 2 but there is no saturation of the curve, because there is no plasma generation. It has to be considered that the Nd:YAG laser output energy without Q-switch is higher of a factor of three in respect of the Q-switch operation, hence this energy expenditure is partially compensated by the better laser efficiency. In Figure4 the operative range for the microsecond regime with SFR laser is reported. It is very wide and the absence of plasma avoids saturation. Consequently the restorer may set up the most suitable fluence without critical side effects. Rising the fluence also the productivity rises linearly, making easy to adapt the settings to the restoration needs. Furthermore no yellowing of stone was observed using SFR laser cleaning, because the slow vaporisation process avoids the problem by itself. An additional advantage of cleaning using SFR lasers in respect of Q-switch lasers is the easy coupling of low intensity microseconds pulses in optical fibres, while high intensity nanosecond pulses may break the fibre facet quite frequently. This SFR laser has been engineered as a reliable laser instrument by EL.EN.Group under the denomination Smart Clean I and II. The two models emit pulses with duration in the range 35-50 microseconds and differ only for the output energy: I J for Smart Clean I and 2 J for Smart Clean II. The beam delivery is provided by a fibre cable long up to 50 m if needed for scaffoldings.

135 In Tuscany in the last years a number of laser restoration were carried out [10] using the SFR laser: in the restoration yard of the church of San Frediano in Pisa, at the Porta della Mandorla by Nanni di Banco in Florence Cathedral [11], at the Porta di San Ranieri of the Cathedral of Pisa, for the many fragments of the original Fonte Gaia by Jacopo della Quercia, formerly set in Piazza del Campo a Siena. In all these restoration activity the SFR laser technique has allowed to discriminate the proper layers removal in very complex stratigraphy overimposing various layers of pigmentation, sulphation, oxalate and so on. Important applications of the technique have been carried out on marble statues severely degraded by exposition for centuries to the sulphation process. Several masterpieces by Donatello (the Prophet Habacuc, the Pulpit in the Prato Cathedral) and Nanni di Banco's Santi Quattro Coronati [12], have been successfully restored using laser cleaning especially when other traditional techniques such as microsandblasting or chemical treatment could not ensure the achievement of the result. This has been the case of gilding traces, left by the action of time in the dresses borders and in the hair. Only the delicate calibration possible with the SFR laser cleaning has allowed preserving them at best. In Greece archaeological pieces such as a marble statue of Hermes, and recently a panel of the west frieze of the Parthenon were cleaned using a Q-switch Nd:YAG laser and combining the emissions at both IR and third harmonic [13]. Their combination of IR and UV radiation could avoid yellowing of the cleaned surface, which was observed using IR emission alone [14, 15].

s.

Laser Cleaning of Metals

Figure 5. Laser cleaning of a Roman coin allows easy reading and dating. On the right a detail from. Porta del Paradiso, by L. Ghiberti, Florence.

Metals experience what is defined as the metal cycle, starting from the mineral, which under the metallurgy techniques invented by other ancestors became metals, then machined in the shape useful for a specific function, finally abandoned and left to the action of oxidation processes and other reactive acid agents present in the air, in the water and in the ground where these objects were lost for centuries. These are the cases of archaeological metals when they are recovered from the excavation sites, or the case of archaeological metals found under the sea. Some examples for testing laser cleaning have been Roman coins completely covered by a thick encrustation of calcareous concretions, with oxides and salts of copper and

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silver. Also other bronze objects, silver objects and iron objects have been submitted to laser cleaning in many trials. In all cases a suitable choice of laser parameters (fluence, wavelength, pulse-width) could discriminate the removal in order to remove the encrustations, without side effects as local melting and preserving stable oxide coatings when they were present. A crucial experience has been made with gold-coated bronze renaissance artworks, where the gilding was suffering a complex deterioration process due to environmental pollution, and leading to micro blistering and loss of the gilding layer. This has been the case of the Porta del Paradiso, a famous masterpiece (1425) by Lorenzo Ghiberti, who won the concourse with Brunelleschi for the most beautiful door of the Baptistry in front of the cathedral in Florence. Many years of analysis and diagnostic studies begun in the 1980 leaded to a chemical approach based on washing with Rochelle salts, in order to clean the outer deposits laying over the gilding layer. Unfortunately washing has determined long term problems of efflorescence of salts. The study of a possible laser approach made possible to clarify that only laser pulses ranging between 100 ns and a few microsecond would allow minimum transient heating to the gold layer, avoiding any local deformation or melting of the gold film[l6]. 111',"1 =

2;F (D)1 1tT

'

This breakthrough originated by a critical analysis of the temperature rise during the transient absorption of laser light: where K is the thermal conductivity, D is the thermal diffusivity and Fa is the laser fluence. In order to avoid the gold film (few microns) suffer any deformation or even melting and loss it is needed to limit the maximum temperature rise. The range over 100 ns duration up to few microsecond ensures that the temperature rise will be limited to two hundreds degrees Co, avoiding any risk of damage for the gold. A Nd:YAG laser operating in Q-switch regime was suitably modified extending the cavity length and achieving a long pulse operation (LQS). After this successful achievement other masterpieces made of gilded bronze were cleaned by LQS laser or SFR laser according to the most appropriate. For example gilding by leaf would be better cleaned using SFR laser with microsecond pulses, because the thickness of the leaf is so small (
6. Laser Cleaning of Paintings, Paper and Polychromes For artefacts composed by materials involving organic fibres and compounds the laser approach encounters the problem of low thermal damage threshold. Furthermore the valuable historical materials have micro dimensional structure with features of sub micron thickness, and this characteristic adds another factor of difficulty to achieve the same selectivity, precision and control well demonstrated for other inorganic materials. The situation here described is the case of paintings, paper and parchment, where the laser cleaning approach has been necessarily different from stone or metals. For the problems encountered in

137

paintings restoration excimer laser ablation was proposed in Greece to achieve sub micron removal of deteriorated varnish and also for repainting removal. The technique was on-line controlled by a LIBS sensor [17], in order to detect any beginning of irradiation of the pigments layer and avoid their unacceptable photo physical darkening. As it was clear in facts, most of inorganic or organic pigments react with very low thresholds to laser radiation producing a change in the colour that has to be absolutely avoided. This is a general problem of pigments [18] based on various metal ions such as copper carbonate (Azurite), lead carbonate (lead white), lead chromate, lead antimonite (Naples yellow), mercuric sulphide (cinnabar), zinc oxide (zinc white), and enamels. Organic pigments also show different degrees of discoloration, but for both types of pigments the presence of varnish avoids the colour change. A project based on this approach [19] developed in The Netherlands a complete system employing an excimer laser, a LIBS sensor and an automated x-y table to position the irradiation spot. Its effectiveness has been validated so far on paintings in The Netherlands. Other groups in USA and Italy are testing the use of Erbium lasers at 2.9 /lm, for the cleaning of deteriorated varnishes on paintings [20].

Figure 6. Cleaning laser system prototype for paper and parchment.

The application of laser techniques for the cleaning of paper and parchment has followed different solutions [21]. For them the organic collagen structure of fibres represents the material to be preserved, besides inks and pigments constituting the graphics or the drawing. Ancient documents on paper or parchment may have problems of readability or conservation, because of accumulated dirt and dust, or fungi and other organic stains. In a series of EC projects a laser cleaning system for high-precision cleaning of flat large area substrates under Laser Class 1 conditions has been developed. It allows restoration of artefacts of organic materials such as paper, parchment, leather, textiles, wood and also inorganic materials such as metals, alloys and ceramics. The laser spot is scanned over the objects through a remote computer control system. A high energy diode-pumped Q-switched Nd:Y AG laser operating at 1064 and 532 nm was installed . The breakthrough result was to understand that the minimum interaction with the collagen fibres was at the green wavelength 532 nm, because of the minimum optical absorption. The workstation features also on-line diagnostic tools such as

138 visible, ultraviolet and fluorescence imaging for the identification and documentation of visible and chemical changes of the irradiated substrate areas. One of the major challenges of precision cleaning was to avoid areas where ink or pigments were present. This was accomplished very precisely by image processing and laser control.

Figure 7. Detail before and after laser treatment of a "brocado" in the Cathedral of Jaca, Spain.

Pigments in frescoes and polychromes in architectures are submitted to several risks of deterioration coming out because of humidity, rain washing, sulphation. An increasing effort is being carried out to approach polychromes found in architectures. An important example of laser cleaning of polychromes has been reported in Spain [22] , from the restoration intervention at the Church of S. Tecla de la Canada (Zaragoza). There were cases of repainting and cases of soot and candle smokes over polychrome chapel arcs and domes. Cases of "brocado" were approached in the Cathedral of Jaca (Chapel of San Miguel). In these cases polychromes are on a metal substrate, now under heavy deterioration and laser cleaning by a Q-switch Nd:Y AG laser was successful to recover the brilliance of the colours without damage to them.

7. Conclusions Laser techniques in conservation are presently a very interesting scientific issue, with significant successful applications and many challenges offering promising fields of research. After more than thirty years of studies and validation the problems put in evidence by the experimentation were successfully assessed by means of specific solutions involving the choice of the laser parameters and determining the most appropriate ablation regime. They are today a well accepted and appreciated professional tool in the hands of restorers. The transfer of scientific and technological findings to laser systems producers and also the transfer of methodology to companies offering restoration services have been a crucial objective of national and European programs. In many countries the national public institutions of conservation have a complete awareness of the innovation determined by lasers in conservation. A number of well renowned masterpieces have been treated by laser cleaning or have been investigated using a laser diagnostic method. The innovation caused by lasers in the conservation sector is sustainable because the advantages in respect with other techniques are now demonstrated, and the improvement in the precision and control of the

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cleaning is actually crucial especially when delicate historical layers have to be preserved. Examples are calcium oxalate on marble, gilding on bronze, paintings, fresco (wall) paintings, antique documents, antique textiles and so on. The use of the laser tools of course has to be restricted to trained restorers, and the development of laser systems equipped with a hand-piece and designed as operator-oriented could meet the end-user favour. As last consideration also cost and reliability of present laser cleaning systems are now acceptable by the endusers, because the last generation of devices has improved their engineering and added a worthwhile value to their performance.

Acknowledgments The authors wish to thank the ICLSA Organising Committee for the financial support, and acknowledge the courtesy of Prof. Wolfgang Kautek and of Prof. Marta Castillejo for availability of Figure 6 and Figure7.

References 1. L. Lazzarini, 1.F. Asmus, M.L. Marchesini, 1st Int. Symposium on the Deterioration of Building Stone, La Rochelle (1972), 89-94. 2. See for example Proceed. of the 9 th Int. Congress on the Deterioration and Conservation of Stone. V. Fassina ed .. Vol. 1-2, Elsevier Science B.V., Amsterdam (2000). 3. V. Verges-Belmin. Restauratorenblatter (1997) 17-24. 4. M.l. Cooper, D.C. Emmony, 1.H. Larson" Optics Laser Technology 27 (1995) 69-73. 5. E. Hontzopoulos, C. Fotakis, M. Doulgeridis, "Excimer lasers in art restoration", SPIE 1810 (1992) 749. 6. C.H.Olainek, K. Dickmann, F. Bachmann, Restauratorenblatter (1997) 89-94. 7. O. Calcagno, M. Koller, 1. Nimmrichter, Restauratorenblatter (1997) 39-44. 8. O. Calcagno "Pulitura laser delle statue del Willigelmo alia porta regia del duomo di Cremona", Conferenza Comune di Cremona (1987). 9. S. Siano, et al., Applied Optics, 36, pp. 7073-7079 (1997). 10. O. Sabatini et al., Journ. Of Cultural Heritage 1,9-19 (2000) 11. S. Siano et aI., in Lasers in the Conservation of Artworks, LACONA V Proceed. Ed. K. Dickmann et aI., 171-178, Springer (2005). 12. S. Siano et al., Journ. Of Cult. Heritage, 4-1 (2003) 123-128. 13. P. Pouli et al., LACONA V Abstract book (2003) 143-145. 14. M. Laboure et aI., Journ. Of Cult. Heritage 1-1 (2000) 21-28. 15. P.Bromblet, M.Laboure, O. Orial, Journ. Of Cult. Heritage 4-1 (2003) 17-26. 16. S. Siano and R. Salimbeni, Studies in Conservation, 46, 269-281 (2001). 17. D. Anglos et al., Restauratorenblatter, 113-118 (1997). 18. M.Castillejo et al., An. Chern, 74, 4662-4671 (2002). 19.1. H.Scholten, 1.M. Teule, V. Zafiropulos, R. M. A.Heeren, Journ. of Cult. Heritage 1, 215-220 (2000). 20. W. Kautek, S. Pentzien, E. Konig, 1. Kruger, Restauratorenblatter, 69-78 (1997). 21. M. L Wolbarsht, A. De Cruz, S. A. Hauger, Journ. Of Cultural Heritage 1, 173-180 (2000). 22. Private communication by CoresaI, Spain.

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11-2. Contributed Papers

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TECHNOLOGY -AIDED HERITAGE CONSERVATION LASER CLEANING FOR BUILDINGS MOHAMED SHOUKR NADA Technical Office Member of Enviromental & Community Service Affairs, Cairo University. Associate Professor of Architectural Engineering, Fayoum University. General Manager of Urban & Architectural Style Control Directorate, The Egyptian National Organization of Urban Harmony, Ministry of Culture.

pai [email protected] Conservation has an important role in bringing the past to life and minimizing the effects of deterioration on the material. There is a range of different treatments for conservation, but it is important to take into consideration to choose suitable techniques and methods for conservation to avoid damage and to use good monitoring, controlling techniques and skilled operators with experience of the process to achieve the most satisfactory results. Cleaning is one of conservation techniques and process, which involve removal of materials from an object or building and to reveal its true conditions, so that appropriate action can be taken to ensure that it survives for many future generations to enjoy. One of the promising Technology-Aided Heritage Conservation (TAHC) for buildings among the cleaning techniques can be Laser cleaning. This research work may address laser uses, techniques, methods, advantages and disadvantages. In addition, it discusses lasers as a method of cleaning architectural detail on historic buildings, rather than large areas of plain stonework. Keywords Technology-Aided Conservation - Urban and Architectural Heritage Conservation Laser Cleaning

1.

Introduction

Conservation can be defined as preservation from loss, depletion, waste or harml . Its also the action which has to be taken in order to prevent causes of decay and manage change dynamically2. Conservation has an important role in bringing the past to life and minimizing the effects of deterioration on the material. There is a range of different treatments for conservation, but it is important to take into consideration to choose suitable techniques and methods for conservation to avoid damage and to use good monitoring, controlling techniques and skilled operators with experience of the process to achieve the most satisfactory results. It is important to know that the main aim of all conservation treatment is to increase the stability of the object being treated. Cleaning is one of conservation ,_ Weaver,Martin E, Conserving Buildings a Manual of Technique and Materials, 1997:1 -Feilden ,Bernard M, Conservation of Historic Buildings, 2003:3.

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techniques and process, which involve removal of materials from an artifact 3 , and "serves not only to improve the aesthetic appeal of an object or building but also to reveal its true conditions so that appropriate action can be taken to ensure that it survives for many future generations to enjoy,,4. There are many different kinds of cleaning methods and techniques such as mechanical and chemical cleaning. However, the choice of cleaning process to use in conservation depend on what will be removed or what will be preserved, this because the distinction between optimum cleaning and over- cleaning is often quite subtle (Figure 1). The method chosen to clean the object must ensure that the cleaning process does not damage the object and the conservator has to make a choice as to the final appearance of the treated object following the cleaning process 5 .

(a) rontaminated

(b) clean

(c) cleaJler

(d) cleanest

(e) over-clean

Figure I.The distinction between optimum cleaning and over- cleaning6 .

Techniques such as micro-blasting will always result in some loss of material from the surface, particularly from a crumbling decayed surface because abrasive particles cannot discriminate between the dirt and the substrate 7 . The loss of surface detail reduces the aesthetic appeal of an artifact and in extreme cases can even lead to deterioration of the material. New technology can offer different methods and process which avoid and minimize damage and giving satisfactory cleaning results. One of the promising Technology-Aided Heritage Conservation (T ARC), for buildings among the cleaning techniques can be Laser cleaning. It has shown a good potential as a cleaning tool in many material categories in conservation

http://epubl.ltu.seI1402-1544/2006/02lLTU-DT-0602-SE.pdf , koh, Yang Sook, Laser Cleaning as a Conservation Technique for Corroded Metal Artifacts,2005 :6. 4 -http://www.buildingconservation.comlarticles/laserllaser.htrn , Cooper,Martin, Recent Developments in Laser Cleaning 5 -http://epubl.ltu.sel1402-l544/2006/02/LTU-DT-0602-SE.pdf, koh, Yang Sook, Laser Cleaning as a Conservation Technique for Corroded Metal Artifacts,2005:7. 6 -http://epubl.ltu.se/1402-154412006/02/LTU-DT-0602-SE.pdf, koh, Yang Sook, Laser Cleaning as a Conservation Technique for Corroded Metal Artifacts ,2005 :7. 7 -http://epubl.ltu.selI402-l544/2006/02/LTU-DT-0602-SE.pdf, koh, Yang Sook, Laser Cleaning as a Conservation Technique for Corroded Metal Artifacts,2005:7. 3 _

145

work 8 • Laser cleaning is an effective technique to provide a high degree of control during cleaning, especially if there is a need to preserve items with surface relief, original tool marking and surface patina9 . It depends on the use of high -intensity light for surface cleaning in order to remove and clean any undesirable contaminant from the reflective underlying surface lO . 2.

What is Laser?

Laser is a unique source of light which provides energy in the form of a very intense monochromatic (i.e. single-coloured), by using well-collimated beam. This can be defined as "the energy per unit area incident on the surface (energy per pulse / beam size at the surface) and is usually measured in joules per square centimeter (J/cm2)"11 . The typical laser beam can spread out only a few millimeters after traveling several meters l2 . When a laser beam interacts with any surface, part of the energy is reflected and the reminder of it is absorbed. The fraction of energy absorbed depends on the wavelength of the laser radiation and on the physical and chemical properties of the surface, its important to know that the laser beam have no effect on a surface unless it is at least partially absorbed 13 .In a typical system the laser head, power and cooling supplies are housed in a single portable unite which weighs about 125 kg and runs off 13AJ240V mains supply. In this case the laser beam is directed by means of a 7-jointed articulated arm with the beam emerging through a pen-like hand piece within which a lens is used to produce a diverging beam l4 .Lasers often share some common properties; they are monochromatic, coherent, have high directionality and usually measured in watts l5 . The light of the laser spreads

-http://epubl.ltu.se/1402-l544/2oo6/02ILTU-DT-0602-SE.pdf ,koh, Yang Sook, Laser Cleaning as a Conservation Technique for Corroded Metal Artifacts,2oo5:iii. 9 _ http://epubl.Itu.se/1402-l54412006/02ILTU-DT-0602-SE.pdf, koh, Yang Sook, Laser Cleaning as a Conservation Technique for Corroded Metal Artifacts,2oo5:3. 10 _ http://epubl.Itu.seIl402- I 544/2006/02lLTU-DT-0602-SE.pdf ,koh,Yang Sook, Laser Cleaning as a Conservation Technique for Corroded Metal Artifacts,2005:5. 11 _ http://www.buildingconservation.com/articles/laser/laser.htm ,Cooper,Martin, Recent Developments in Laser Cleaning 12 _ http://www.buildingconservation.com/articles/laser/laser.htm ,Cooper,Martin, Recent Developments in Laser Cleaning 13 _ http://www.buildingconservation.com/articles/laser/laser.htm ,Cooper,Martin, Recent Developments in Laser Cleaning 14_ http://www.buildingconservation.com/articles/laser/laser.htm ,Cooper,Martin, Recent Developments in Laser Cleaning 15 -http://epubl.ltu.se/1402-l544l2oo6/02/LTU-DT-0602-SE.pdf, Koh, Yang Sook, Laser Cleaning as a Conservation Technique for Corroded Metal Artifacts,2005:9 B

146

out very slowly from the source which means that the laser is able to deliver energy to a surface in a highly controllable manner 16 . Cleaning by laser irradiation involves complex mechanisms such as photothermal, photochemical and mechanical effects on target material 17 • The exact mechanisms which are active depend on the parameters of the laser irradiation and on the physical and chemical prosperities of the surface (Figure.2).

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3.

.

Intervention of Laser

The modern theory of light has begun in the work of Isaac Newton in the 1700s, but the most important theory about lasers was suggested first by Albert Einestine in 191i 9 • In 1957, Charles H.Townes invent the maser (microwave amplification by the stimulated emission of radiation). In 1960, Theodore Maiman demonstrated the first laser which used synthetic ruby, which emitted coherent light at a single wavelength 694 nm at the red end of the visible spectrum20 • After that, many different types of laser have been developed and applied in a wide range of fields. Each type of laser emits a characteristic http://www.liverpoolmuseums.org.uklconservation/technologiesllasercourse p2.asp , Introduction to laser cleaning in conservation Laser cleaning, How does laser cleaning work ? 17 -http://epubl.ltu.seIl402-l544/2006102ILTU-DT-0602-SE.pdf, Koh, Yang Soak, Laser Cleaning as a Conservation Technique for Corroded Metal Artifacts,2005: 11 18 -http://epubl.ltu.selI402-l544/2006102/LTU-DT-0602-SE.pdf, Koh, Yang Soak, Laser Cleaning as a Conservation Technique for Corroded Metal Artifacts,2005:12 19 _ http://epubl.ltu.selI402-154412006102lLTU-DT-0602-SE.pdf, koh, Yang Sook, Laser Cleaning as a Conservation Technique for Corroded Metal Artifacts,2005:9 20 _ http://epubl.ltu.se/1402-l544/2006102ILTU-DT-0602-SE.pdf , koh, Yang Soak, Laser Cleaning as a Conservation Technique for Corroded Metal Artifacts,2005:9 16 _

147

wavelength (infrared IR, visible or ultraviolet UV regions) (Figure. 3), dependent on the type of material that emits the laser light, the laser's optical system, and the way the laser is energized 21 • Lasers come in a wide range of power levels from less than a mill watt to many kilowatts.

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Figure. 3. The electromagnetic spectrum and examples of lasers used to generate at different frequencies 22 .

4.

Uses of Laser

The use of laser cleaning has now become common and available in a number of specialized conservation studios. It is most widely applied to sculpture and monuments to provide sensitive and high-quality cleaning. The use of laser cleaning on buildings has tended to be restricted to areas of sculptural and architectural details, where cleaning of the highest quality is required 23 . -http://epubl.ltu.se/l402-l544/2006102lLTU-DT-0602-SE.pdf, Yang Sook, Laser Cleaning as a Conservation Technique for Corroded Metal Artifacts,2005:9 22 -http://epubl.ltu.selI402-1544/2006/02ILTU-DT-0602-SE.pdf, Koh, Yang Sook, Laser Cleaning as a Conservation Technique for Corroded Metal Artifacts,2005: 10. 23 _ http://www.donhead.comlvol ll3.htrn , Cooper,Martin,Laser Cleaning of Sculpture, Monuments and Architectural Details. 21

148

The most commonly used laser cleaning systems in conservation is the Qswitched Nd: Y AG laser which is usually employed for stone cleaning24. It is extremely reliable, easy to maintain, relatively compact and robust 25 . The Nd: Y AG laser emits short pulses( typically 5-10 ns long) of infrared radiation at a wavelength of 1064nm (or 1.064 x 1O_6m)26. Light at this wavelength has successfully been used to remove dirt and other coatings from a wide range of materials including marble, lime stones, sandstones, terracotta, alabaster, plaster, aluminum, bone, painting, stained glass, ivory and vellum, which show a high contrast between absorption and reflection of the surface contaminants and the substrate27 . It interacts strongly with many unwanted dirt layers and surface accretions, leading to their removal from the artwork. This is caused by the laser quickly heating the dirt, which expands and comes away from the surface. This type of laser is commonly used since most soiling layers are much more strongly absorbing than the underlying substrate at 1064 nm28 in many cases, the light interacts only weakly with the surface of the artwork. This means that providing cleaning is carried out within safe parameters, once the dirt has been removed, further pulses will have no effect on the surface, and the removal process stops as soon as the clean surface is exposed 29 . Therefore, its possible for a conservator to completely remove unwanted layers without over cleaning the valuable surface of the artwork. He controls the cleaning effect through adjustments to the energy in each pulse, the number of pulses fired per second and the distance between the tool and the surface3o . All this lead to preserve any important surface coating, patina and fine surface detail (Figure. 4). Another type of lasers is TEA C02 lasers, which has been successfully used for removing paint from aircraft. "This is due to the fact that the absorption coefficient of paint materials consisting of organic or inorganic compounds is much higher than that of the aluminium substrate,,3! http://www.worldstonex.com/eniInfolten.asp?ICat=128&ArticleID=23 ,Laser Cleaning of Stones. 2~ _ http://www.buildingconservation.com/articles/laser/laser.htm ,Cooper,Martin, Recent Developments in Laser Cleaning 26 _ http://epubJ.ltu.selI402-l54412006/02lLTU-DT-0602-SE.pdf, Koh, Yang Sook, Laser Cleaning as a Conservation Technique for Corroded Metal Artifacts,2005:35. 27 http://epubJ.ltu.se/1402-1544/2006/02/LTU-DT-0602-SE.pdf, Koh, Yang Sook, Laser Cleaning as a Conservation Technique for Corroded Metal Artifacts,2005:35. 28 _ http://www.buildingconservation.com/articles/iaser/laser.htm ,Cooper,Martin, Recent Developments in Laser Cleaning 29 -http://www.liverpoolmuseums.org.uk/conservationltechnologies/lasercourse p2.asp, Introduction to laser cleaning in conservation Laser cleaning, How does laser cleaning work ? 30 -its important to know that the distance between the tool and the surface controls the intensity or spread of the beam, http://www.buildingconservation.com/articies/laser/iaser.htm. Cooper,Martin, Recent Developments in Laser Cleaning 31 -http://epubJ.ltu.selI402-154412006/02/LTU-DT-0602-SE.pdf, Koh , Yang Sook, Laser 24 _

149

Figure. 4 .A Greco -Roman marble head excavated in Shropshire - left after laser cleaning with an Nd: Y AG laser and far left, coverd in soil and whitewash.

The most important cleaning parameter is the energy density, or fluence that should be high enough to remove the dirty layers. This fluence must also be low enough to ensure that the substrate surface is not damaged 32 . Since most types of soiling absorb strongly at l.064mm, cleaning can usually be carried out relatively low fluence ( «IJ/cm2 ) to minimize any risk of damage to the substrate because strong absorption leads to rapid heating and subsequent expansion of a dirt partical33 . In order to enhance the laser cleaning effect, water can be used for this purpose by brushing or spraying a thin coating onto the dirt surface so stubborn deposits of dirt can be removed without having to increase the fluence to unacceptably high levels. By this way, dirt particles become coated with a film of water . The addition of water usually increases the cleaning rate significantl y34 .

5.

Laser Techniques and Methods

There are two general methods of laser have been developed during the last years:

Cleaning as a Conservation Technique for Corroded Metal Artifacts,2005:35. 32-http://epubl.ltu.se/1402-l54412006/02/LTU-DT-0602-SE.pdf , Koh, Yang Soak, Laser Cleaning as a Conservation Technique for Corroded Metal Artifacts,2005 :35. 33-ht1p://www.buildingconservation.comlarticles/laser/laser.htm. Cooper,Martin, Recent Developments in Laser Cleaning 34-ht1p://www.buildingconservation.comlarticlesllaserllaser.htm. Cooper,Martin, Recent Developments in Laser Cleaning

150

1-

2-

6.

Dry laser cleaning (DLC): the surface is irradiated by a short laser pulse. It is assumed that the thermal expansion of the substrate surface plays the major role in the cleaning mechanism as it is thought to accelerate to particle and lead to inertia forces to overcome the adhesion force acting on the particles35 .This technique is useful when the substrate and contaminant layer or particle heated by the laser pulse leading to their ejection or vaporization36 • Steam laser cleaning (SLC): a transparent liquid is condensed onto the surface just before the laser pulse. When the liquid is heated via heat diffusion , particle removal is governed by bubble nucleation and growth at the solid-liquid interface and the subsequent explosive evaporation of the liquid film 37 .

Lasers and the Architectural Details

In cleaning architectural details, a conservator is bound by a professional code of ethics to use techniques that are not abrasive and do not change the original surface color, appearance, texture, and composition. In addition to, concerns about the safety of the procedures38 . There are two types of contaminates to be cleaned from artifacts; foreign matter that has become mixed with the original material, and materials resulting from the chemical and physical deterioration. There are several techniques for analyzing and cleaning architectural details 39 : 1- "Methods include laser-induced fluorescence, where a low-intensity laser gives a fluorescence emission identifiable by its spectral feature to analyze both organic and inorganic materials, such as paints and varnishes,,40. 2- Laser -induced breakdown spectroscopy (UBS), by this technique the spectrum of ionized material is analyzed and the encrustation on metal and stone is ablated . UBS can give more selective, unambiguous results than laser induced fluorescence. 3- Raman spectroscopy, this can be defined as nondestructive laser-based technique in which a laser beam is reflected off a sample and the http://www.uniknostanz.de!FuFlPhysik/LeidererlResearchlDynamics_oCThin_FiImslLaser_ Cleaningllaseccleaning.htm 36 -http://epubl.ltu.seIl402-1544/2006/02ILTU-DT-0602-SE.pdf, Koh, Yang Soak, Laser Cleaning as a Conservation Technique for Corroded Metal Artifacts,2005:12. 37 _ http://www.uniknostanz.de!FuF/PhysiklLeiderer/ResearchIDynamics_oCThin_FilmslLasec Cleaningllaser_cleaning.html . 38 _ htpp:llwww.osa-opn.orglsurvey.cfm , Dawes,Daniel, Lasers and the Fine Art of Art Conservation. 39_ htpp:llwww.osa-opn.orglsurvey.cfm, Dawes,Daniel, Lasers and the Fine Art of Art Conservation 40_ htpp:llwww.osa-opn.orglsurvey.cfm, Dawes,Daniel, Lasers and the Fine Art of Art Conservation 35

151

wavelength that are different from that of the laser are measured. In this technique, the pigments under study are identified through matching of the wavelength of their molecular chemical bonds. Lasers, which induced Fluorescence (LIP), Breakdown Spectroscopy (LIBS) and laser Raman Spectroscopy can be used not only for cleaning or for the analysis of pigments and binding media, but also can be used for determining the degree of ageing and oxidation polymerization process 41 . LIBS presents several interesting possibilities for elemental and in-depth analysis, also, it may be combined with cleaning application. 7.

Principles of Laser-Stone Interaction

The optical characterization of the stone surface including alteration layers and patinas, is the first investigation step to understand the basics of laser cleaning of stone. The response of stone materials to high energy laser pulses at levels suitable for stone cleaning has been studied by means of coherent imaging diagnostics that permitted the observance and analyzing of the very fast processes occurring during laser-stone interaction 42 • It has been found that the short laser pulses in the nanosecond range are more like to cause mechanical damage to the surface of the irradiated material, micro fragmentation and increased porosity of the substrate. The risk of thermally -induced modifications is greater with longer duration pulses up to the millisecond range, where the typical effects of continuous irradiation can be recognized 43 . An experiment has been done on a large collection of stone sample that was obtained from Italian monuments (especially from Siena and Florence), presenting various degradation, and using three different Nd:YAG laser types, one of them (SFR) which is the prototype version of the system developed (Figure. 5). Three main intrinsic aspects has been pointed: l-"Laser cleaning is very precise and progressive because it removes layers of few microns for each laser pulse. This means that cleaning operation follow the microstratigraphy of the alteration layers and can be interrupted at predetermined stratigraphic levels ,,44.

41_

42

http://www.arcchip.czlwl21w12_pouli.pdf. Pouli,P,Lasers in Art Conservation. State of the Art on the Fundamental Research and the Applications carried out at FORTH-IESL . -http://www.worldstonex.com!enllnfolten.asp?ICat=128&ArticIelD=23 ,Laser Cleaning of Stones

-http://www.worldstonex.comlenllnfolten.asp?ICat= 128&ArticleID=23 ,Laser Cleaning of Stones. 44 -http://www.worldstonex.comlenllnfolten.asp ?ICat= 128&Artic1eID=23 ,Laser Cleaning of Stones. 43

152

2- Very weak and highly altered surface can be successfully treated. 3-Chemically complex surface can be cleaned.

Figure. 5 . Phases of laser cleaning on a sample of marble with black crusts collected from the Baptistery of Siena. Fig 3a & fig 3b ," is a stereomicroscopic image of the between cleaned uncovered a well preserved patina of calcium oxalate, where traces of grooves from the original working are still recognizable ,,45

There are also many successful demonstrations of laser cleaning of different types of stone and painted artwork. It could be stated that the success of any laser cleaning application relies on the degree of confinement of the thermal, mechanical and chemical effects, which operate for the removal of the undesired layers 46 •

8.

Laser Cleaning as a Conservation Technique for Corroded Metal Artifacts

"Laser cleaning is an effective technique for assisting in the conservation of metal artifacts since it provide a high degree of control during allowing fragile objects or items with a consideration amount of surface detail to be effectively cleaned ,,47 The main advantages of using pulsed for cleaning metallic

http://www.worldstonex.com!enlInfolten.asp?ICat= 128&ArticleID=23 ,Laser Cleaning of Stones. -http://www.arcchip.cz/w12/w12_pouli.pdf. Pouli,P,Lasers in Art Conservation. State of the Art on the Fundamental Research and the Applications carried out at FORTH-IESL. -http://epubl.ltu.seIl402-1544/2006/02ILTU-DT -0602-SE.pdf , koh, Yang Sook, Laser Cleaning as a Conservation Technique for Corroded Metal Arti facts,2005: 3.

45 _ 46

47

153

archaeological artifacts is that the removal of the crust is well controlled and can be carried out layer by layer . The TEA C02 laser is very suitable for cleaning organic materials from metal artifacts (Figure. 6).

Nd:'1 AG-laser

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9.

Advantages of Laser Cleaning

The increasing of using laser cleaning through out the world due to: 1- Selectivity, its possible to remove layers of dirt without removing any original material from the surface. 2- Non-contact, because the energy is delivered in the form of light so there is no mechanical contact with the surface. 3- Localized action, the laser cleans only where directed. 4- Immediate control and feedback, the condition of the surface can be continuously monitored by the conservator during cleaning. 5- Versatility and reliability. 6- Low environmental impact. 7 - Preservation of surface relief.

10. Disadvantages of Laser Cleaning 1-

48

Laser cleaning does not work on everything. The cleaning of polychrome sculpture leads problems because the different pigments absorb different amounts of radiation.

-http://epubl.ltu.seI1402-1544/2006/02lLTU-DT-0602-SE.pdf , koh, Yang Sook, Laser Cleaning as a Conservation Technique for Corroded Metal Artifacts,2005:36

154

2-

High cost of purchasing.

Conclusion

From what presented in this paper , the following general conclusion can be reached: "The development of laser cleaning systems in conservation has been driven by a desire to refine methods of cleaning employed by conservators. Quality rather than speed has, over the years, been the primary concern of conservators and scientists working in this field. This is the main reason that lasers have often been restricted to the cleaning of sculptural and architectural detail on historic buildings, rather than large areas of plain stonework,,49. When selecting a laser for cleaning, the physical and chemical prosperities of the material must be considered. It is important to use good monitoring and controlling techniques to achieve the most satisfactory results. References

Feildem,Bernard M, "Conservation of Historical Buildings ", Architectural Press, Third edition 2003. 2. Weaver,Martin E,"Conserving Buildings A Manual of Techniques and Materials ", Preservation Press,Jan 1997. 3. C.Fotakis ,"Lasers for art's sake!", Optics and Photonics News 6 (N05),30-35 (1995 ). 4. V.Zafiropulos, S.Georgiou, D.Anglos ,"Lasers in Art Restoration ", Optics and Photonics News (OPN) ,4-5 (November 1999 ). 5. Koh,Yang Sook, "Laser Cleaning as a Conservation Technique for Corroded Metal Artifacts",2005, http://epubl.ltu.se/14021544/2006/021LTU-DT -0602-SE.pdf. 6. Cooper, Martin,"Recent Developments in Laser Cleaning", http://www.buildingconservation.comlarticles/laser/laser.htm ( accessed 16 February 2006 ). 7. Cooper, Martin," Laser Cleaning of Sculpture, Monuments and Architectural Details", http://www.donhead.comlvoI1l3.htm ( accessed 16 February 2006 ). 8. Cooper, Martin," Laser cleaning for historical buildings" ,context 72: dec 2001, http://www.ihbc.org.uk/contexCarchiveI72/laser/cleaning.htrnl 9. "Introduction to laser cleaning in conservation Laser cleaning, How does laser cleaning work 1.

49

-http://www.ihbc.org.uklcontext_archivel72/laser/cleaning.html. Cooper,Martin, Laser Cleaning for historical buildings ,context 72: dec 2001

155

10.

11.

12.

13.

http://www.liverpoolmuseums.org.uk/conservationitechnologies/lase rcourse p2.asp (accessed 16 February 2006 ). "Laser Cleaning of Stones", http://www.worldstonex.com!enllnfolten.asp?ICat=128&ArticleID=23 ( accessed 18 February 2006 ). Pouli,P, "Lasers in Art Conservation", State of the Art on the Fundamental Research and the Applications carried out at FORTHIESL , http://www.arcchip.cz/wI2/wI2 pouli.pdf (accessed 18 February 2006) Group of Prof. Dr. Leiderer , ( Laser Cleaning", http://www.uniknostanz.delFuFlPhysiklLeidererlResearchIDynamics 0 f Thin FilmslLaser Cleaning/laser cleaning.html( accessed 18 February 2006 ). Dawes,Daniel, "Lasers and the Fine Art of Art Conservation", htpp://www.osa-opn.orglsurvey.cfm (accessed 20 February 2006).

156

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TECHNOLOGY SIGNIFICANCE IN CONSERVATION OF THE BUILT HERITAGE 3D VISUALIZATION IMPACT MOHAMED SHOUKR NADA

Technical Office Member of Enviromental & Community Service Affairs, Cairo University. Associate Professor of Architectural Engineering, Fayoum University. General Manager of Urban & Architectural Style Control Directorate, The Egyptian National Organization of Urban Harmony, Ministry of Culture.

pai [email protected] Conserving the built heritage, including architectural and urban monumental sites, has its various methods and tools for restoration. Restoration can be considered as a tool used by archaeologists for preserving monuments. Then, engineers have to play their role in developing different methods and techniques for conservation, and rehabilitation if needed, of the architectural and urban heritages. Accordingly, technological advancements may result in providing a futuristic vision of the project, without conducting experiments on the monument itself exposing it or its elements to distortion or deterioration. This research aims to show up the role and significance of technology and new tools in the conservation of historical built heritage, which may be considered via: • •

Addressing the concept of conservation and restoration and its evolution over time. Revealing new methods and techniques for conservation.

Hence, the research may result in highlighting the role and uses of technology in conservation, comprising: • •

Documentation of the built heritage. Computers programs capabilities that can assist in conservation and rehabilitation.

KEYWORDS Information Technology Aided Conservation, Built Heritage Conservation, 3D Visualization

1.

Introduction

Right from the beginning of the first civilization, documentation of events, historical buildings, culture and significant structure has been of utmost importance for further study and preservation. Historical building can be defined as the one that gives sense of wonder and makes us want to know more about the people and culture produced, even if the first impact is always emotional. The historical buildings have architectural, aesthetic, historical, documentary, archeological, economic, social, and even 157

158

political and spiritual values l . "If it has survived the hazards of 100 years of use-fulness, it has a good claim to being called historic".2 Conservation of cultural heritage for future should be one of the most important activities in our societies. The information, which we can gather from such material, is a valuable key in understanding the past. In recent years, a wide range of techniques have been employed to improve and to facilitate conservation work, which avoids damage and increases the state of preservation of cultural heritage. The uniform and universal causes of decay in an historic building may include the actions of man (which probably produce the greatest damage), and diverse climatic and environmental effects3. Atmospheric pollution and traffic vibration must be considered, and earthquake and flood hazards should be assessed. The key to a successful conservation is a complete understanding of the material from which an artefact is made and the associated process of decay. However, for many materials, the processes of decay are complicated and are still far from clear4. The first essential in approaching an historic building in need to repair, is to determine the cause of decay and to remove or minimize its effect5. So each action involving a physical intervention must be carefully considered and tested against the highest professional and technical standards before the actual intervention takes place6.

2.

The Approaches to Restoration

The treatment of ancient monuments and works of art of the past can be seen to have evolved in three different approaches: 1- The traditional approach, which has probably existed for long in society, in which historic structures are preserved as long as they continue to have use values, or because there is no specific reason for their destruction7 .

Feilden, Bernard M, Conservation of historic Buildings, 2003:1 Feilden, Bernard M, Conservation of historic Buildings, 2003:1 3 _ Feilden, Bernard M, Conservation of Historic Buildings, 2003: I. 4-http://epubl.ltu.seIl402-1544/2006/02ILTU-DT-0602-SE.pdf, koh, Yang Sook, Laser Cleaning as a Conservation Technique for Corroded Metal Artifacts,2005:5. 5 -Ashurst, John, Conservation of building &decorative stone ,1999: 1. 6 _ Weaver, Marin E, Conserving Buildings -a Manual of Techniques and Materials, 1997: I. 7 _ Jokilehto, Jukka, Conservation Principles and Their Theoretical Background, 1988:267. 1_

2 _

159

2-

Romantic restoration is the second approach, which has raised in the Italian Renaissance. This approach respects the achievement of past generations, as reflected in the approach of Leon Alberti, and seen in a certain reluctance to destroy even mediaeval structures 8 .

3-

The third approach is "aiming at the conservation and reevaluation of the authentic object, preservation of its historic stratification and

original

material,

and

avoidance

of

falsification ... 9 Conservation can be defined as preservation from loss, depletion, waste or harm lO .Its also the action which has to be taken in order to prevent causes of decay and manage change, dynamicallyll. There are a range of different treatments for conservation. But, it is important to take into consideration to choose suitable techniques and methods for conservation to avoid damage. And, to use good monitoring, controlling techniques and skilled operators with experience of the process to achieve the most satisfactory results. The modern principles of conservation can be conceived in the following words, "Imbued with a message from the past, the historic monuments of generations of people remain to the present day as living witnesses of their ageold traditions. People are becoming more and more conscious of the unity of human values and regard ancient monuments as a common responsibility to safeguard them for future generations is recognized. It is our duty to hand them on the full richness of their authenticity." 12

Jokilehto, Jukka, Conservation Principles and Their Theoretical Background, 1988:268. Jokilehto, Jukka, Conservation Principles and Their Theoretical Background, 1988:267. 10 _ Weaver, Martin E, Conserving Buildings a Manual if Technique and Materials, 1997:1 II -Feilden, Bernard M, Conservation of Historic Buildings, 2003:3. 12 -Venice charter, 1964.

8 _

9 _

160

3.

Ethics of Conservation

The Following standard of ethics ' must be taken into consideration in conservation work l3 : 1-

The condition of building must be documented before any intervention.

2-

Historic evidence must not be removed, destroyed or falsified.

3-

The intervention must be the minimum necessary.

4-

The methods and materials that are used during intervention must be documented.

It's important to note that any proposed intervention must be reversible or at least not prejudice a future intervention whenever this becomes necessary. It must allow the maximum amount of existing material to be retained and be harmonious in colour, tone, texture, scale and form. The intervention should be less noticeable than original material and being identifiable at the same time l4 . All treatments should take account of the original shape and surface details, materials adhering to the artefacts and also the original nature of the remaining material l5 .

4.

Technology Applications in Conservation and Documentation The science of conservation has grown out of an earlier craft tradition of

restoration and now, involves the application of the theory and practice of technical methods to conservation procedures. Applying conservation techniques demand, not only, a high degree of manual skill, but also, acknowledge of material science and early technology combined with an aesthetic sense l6 . It is important to use the suitable techniques,

Feilden, Bernard M, Conservation of Historic Buildings, 2003:6. Feilden, Bernard M, Conservation of Historic Buildings, 2003:6. 15 -http://epubl.ltu.seI1402-1544/2oo6/02/LTU-DT-0602-SE.pdf, koh, Yang Sook, Laser Cleaning as a Conservation Technique for Corroded Metal Artifacts,2oo5:6. 16 -http://epubl.ltu.seIl402-1544l2oo6/02ILTU-DT-0602-SE.pdf, koh, Yang Sook, Laser Cleaning as a Conservation Technique for Corroded Metal Artifacts, 2005:6. 13 _ 14 _

161

which depend upon the conditions of climate to which cultural properly is likely to be subjected. The rapid development of information technology (IT) at the end of the last century has led to the realization that without the application of modern techniques in archaeology and conservation, it's not possible to keep up to date of the demanding conservation process, especially, in documentation process. Various methods of visual communication developed over a period of time from ancient technique, to 2-dimensional technique to today's digital techniques. Architectural heritage preservation makes necessary to produce initial technical documentation to be able to establish the necessary plans and studies that allow later development of suitable approaches and criteria for appropriate buildings interventions. The use of new techniques offer a wide data base and makes it possible to make more reliable interpretation of the results, which are integral parts of the conservation project. The integration of photogrammetric and geographic analysis, through the employment of computer documentation system, permits precise documentation, rabid access to data and elaboration with new methods 17 . Documentation of cultural heritage objects is not an end in itself, but serves as a tool to make information accessible to those who cannot investigate the object itself. Different reasons can be found for the necessity of this information transfer I 8: •

The object is not accessible to interested parties.

•

The object is too large or complicated to be overlooked.

•

The object is visible only for a short period of time at its original location.

•

17

18

Persons living far from the object and cannot afford to visit it.

-http://cipa.icomos.orglfileadmin/papers/antalyal41.pdf, F.Karsli, E.Ayhan E.Tunc, Buiding 3d photo-texture model integrated with GIS for architectural heritage conservation _ http://Cipa.icomos.org/fileadminipapers/antalyal4I.pdf, F.Karsli, E.Ayhan E.Tunc, Buiding 3d photo-texture model integrated with GIS for architectural heritage conservation.

162

•

The object is in danger of slow deterioration or sudden destruction.

Contemporary approaches have to be used to carry out documentation procedure. At this stage, digital photogrammetric techniques and GIS (Geographical Information System) integration would be one of the best solutions. These techniques allow us, not only, to edit some plans with a high degree of graphic precision and metric accuracy, but also, to detect those defects or structural and constructive degenerations that cause the minimum deformations in the formal state of the buildingt9.

s.

Digital Photogrammetry

"Photogrammetry is the technique of measuring objects (2D or 3D) from photogrammes. We say commonly photographs, but it may be also imagery stored electronically on tape or disk taken by video or CCD cameras or radiation sensors such as scanners,,20. Its most important feature is the fact that the objects are measured without being touched. The basic idea of architectural photogrammetry is to reconstruct the imaging geometry, in order to derive object coordinates. However, the three dimensions of the object are reduced in the photograph to a two-dimensional image space. This is why three-dimensional object coordinates cannot be derived from one image. Photogrammetry therefore, combines information from two appropriate images to survey a three - dimensional object.

http://cipa.icomos.orglfileadminipapers/antalyaJ41.pdf, F.Karsli, E.Ayhan E.Tunc, Buiding 3d photo-texture model integrated with GIS for architectural heritage conservation. -http://www.univie.ac.atlLuftbildarchiv/wgv/intro.htm. ,Introduction to Photograrnmetry.

19 _

20

163

Figure 1.Photogrammetric Recording Procedures

"Photogrammetry is a technique whereby information about the position, size and shape can be attained.,,21 Multi-image photogrammetery is a photogrammetric image, which places very few constraints on image configuration. The object of interest is photographed from several viewpoints and directions. The position of the projection as well as lens distortion are known in the reference system. The frame from all the images relating to an object is reconstructed by computer programme from the measurements of a few points, measurements in the images can be converted to true object sizes with high degree of precision. The determination of point and line information provides data from which true -to

21

-http://cipa.icomos.org/fileadminJpapers/antalya/41.pdf, F.Karsli, E.Ayhan E.Tunc, Buiding 3d photo-texture model integrated with GIS for architectural heritage conservation

164

scale building sketches can immediately be produced with computer programmes (Figure. 1) 22. Comparing to classical surveying methods, photogrammetry offers several advantages. Filed operations are reduced to the acquisition of photographs and the measurement of a few control points."In this way, any detail of the building, which is photographed in at least two images, can be subjected to photogrammetric restitution 23 . Principally, Depending on the lense-setting, photogrammetry can be divided into 24 : •

Far range photogrammetry.

•

Close range photogrammetry.

•

Aerial

photogrammetry

(which

is

mostly

far

range

photogrammetry). It is mainly used to produce topographical or thematical maps and digital terrain models. •

Terrestrial

Photogrammetry

(mostly

close

range

photogrammetry).

6.

Photogrammetry and GIS

There have been many applications of photogrammetry techniques and technology since the development of its science, especially, in the recording and documentation of monuments and sites. Developments in the sciences of photogrammetry and image processing over the past decades have seen an increase in the automation of the data collection process, ranging from high precision industrial applications through simple solutions for non traditional users 25 •

-Lamei,Saleh, Dar Al-Aytam complex Old City of Jerusalem Case study on Photogrammetric Recording. 23 _ http://cipa.icomos.orglfileadminlpapers/antalyal41.pdf, F.Karsli, E.Ayhan E.Tunc, Buiding 3d photo-texture model integrated with GIS for architectural heritage conservation 24 _ http://www.univie.ac.atlLuftbildarchiv/wgv/intro.htm.. Introduction to Photogrammetry 25 -http://cipa.icomos.orglfileadminlpapers/antalyal41.pdf, F.Karsli, E.Ayhan E.Tunc, Buiding 3d photo-texture model integrated with GIS for architectural heritage conservation 22

165

Figure. 2 .Visualization of3D model in Arc view

The GIS is a relatively new technology that joins computer science advantages with the modern systems of data capture. It allows the integration and treatment of different types of information of a computer team (Figure. 2). A GIS includes software and hardware tools and a group of procedures elaborated to facilitate administration, analysis, modeling, and editioning to solve any type of planning, storage, and so on information concerning problem26 .

7.

Advantages of Digital Photogrammetry and the GIS 27 •

Have a graphic database of quality, which can work in a coordinated way.

•

Provide basic instruments for the coordination and pursuit of the work and carried out studies for development.

26

27

•

Facilitate the access and bring up to date of various information.

•

Reduce the costs in data obtaining.

-http://cipa.icomos.orglfileadrninfpapers/antalya/41.pdf, F.Karsli, E.Ayhan E.Tunc, Buiding 3d photo-texture model integrated with GIS for architectural heritage conservation -http://cipa.icomos.orglfileadrninfpaperslantalya/4I.pdf, F.Karsli, E. Ayhan E.Tunc, Buiding 3d photo-texture model integrated with GIS for architectural heritage conservation

166

•

Facilitate the exchange of data between diverse organisms and companies.

8.

3d Modeling (Computer Graphics)

Computer-generated graphics have become very common in many areas. Engineers, architects and others have turned to Computer Aided Design (CAD) systems in preference to the traditional drawing board. "Computer graphics have long been used in archaeology and in museums for everyday tasks such as recording excavation plans, illustrating artefacts and presenting the results of scientific analyses. Today, they are also increasingly used both to help archaeologists examine possible 'reconstructions' and in museums as means of presenting this information to the public." 28 "Virtual modeling packages allow the manipulation and reconstruction of objects inside the computer. Fragments or pieces that are missing, or have been badly damaged on the original can be replaced on the virtual image. Nonoriginal details can also be removed; allowing the object to be viewed as we believe was originally intended.,,29 Accurate analysis of the rate of erosion can be determined through this process, which can help to decide if or when any treatment should be carried out. High-resolution 3D models of museum objects and heritage sites contains a wealth of information that can be examined and analyzed for a variety on conservation, research, and display applications. In the case of a site that must be closed or subjected to limited access for conservation reasons, an immersive 3D virtual reality theater can be used to enable visitors to virtually visit the site 3o .

28

-http://www.cs.kent.ac.uklpeople/staff/nsr/arch/visrcantlvisircant.htrnl, Visualising Roman Canterbury: Computer Graphics in Archaeology.

29 -http://www.liverpoolmuseums.org.uklconservationltechnologies/3drecordin~p2.asp,

Conservation Technologies, 3D recording 13D scanning - the applications http://siba3:unile.itlcttel3ddb/silkroadlsilkroad-paper.pdf, Applications of high-resolution 3D imaging to the Recording and Conservation of Ancient Crypt and Grotto Sites.

30 _

167

Computer-based visual enhancement and analysis techniques, which can be applied to accomplish some virtual restoration techniques. 3D models recorded before and after an actual conservation treatment, can serve as vital archival records for ongoing site monitoring and maintenance3l . Models may be generated using a CAD or other modelling program as a means of drawing and placing the basic shapes of the buildings. The building models are based on the available evidence from excavations and the interpretations placed on that evidence by archaeologists and architectural historians. Usually, this means starting from a plan of incompleted surviving foundations, although, in some cases, the remains may be recognizable as a well-known form of building such as a temple. More often, though, the remains are fragmentary and may not give a clear impression of the extent or form of the building. Here, the interpretation is necessarily speculative, guided by a specialized knowledge of the range of possibilities for the architecture of the period and the materials available in the region (Figure. 3)32.

Figure 3. 3D images for Canterbury temple precirict

http://siba3:unile.itlctte/3ddb/silkroad/silkroad-paper.pdf, Applications of high-resolution 3D imaging to the Recording and Conservation of Ancient Crypt and Grotto Sites. _ http://www.cs.kent.ac.uklpeople/staff/nsr/archlvisrcantlvisircant.html, Visualising Roman Canterbury: Computer Graphics in Archaeology.

31_

32

168

According to a photograrnrneric study of the Great Temple in Petra, Jordan. The steps of producing a model can be deducted as follows 33 : •

Photographs of the entire project must be taken, three images of each element with a good degree of angular separation between each image. Each photo is taken at a different position.

Figure .4.

•

To ensure a high level of accuracy the camera/lens setup is calibrated using a program supplied by PhotoModeler. This process determines the degree and extent of error present in the lens, so that each image produced by it can be corrected in the PhotoModeler program.

33

-http://www.lems.brown.eduJ-vote/photogrammetry_index.html, Photogrammetric Digital Reconstruction in Archaeology The Great Temple at Petra, Jordan

169 •

The photographic slides were scanned at a 1200 dpi, formatted as jpeg files and imported into the PhotoModeler Pro program for marking, referencing and processing.

•

Using a series of photos of an area of the temple, object points are marked on each photo, and then referenced between photos (Figure. 4).

Fi1!ure 5.

•

Scaling the Model, this is done by entering the real distance between set points measured during the recording procedure, by using control points measured by team. Then, exact dimensions are added after marking those control points on related photos to result a model (Figure. 5).

Conclusion According to what mentioned in this paper, it may be easily realized that the computing power at the PC level has increased tremendously and has allowed

170

the users to demand better user interface. This need has forced the world of computers to increase interactivity. There will be soon a time where person beyond the realms of his own home for experiencing or studying various aspects of any intricate Heritage Structure. The associated information like history, architectural data, archaeological data, cultural and also traditional audio will be available at the click of the mouse. References 1234567-

8-

9-

10-

Ashurst, John., Dimes, Francis G., "Conservation of building &decorative stone ",1999. Feilden, Bernard M, "Conservation of historic Buildings, third addition", Architectural Press, 2003. Jokilehto, Jukka, "Conservation Principles and Their Theoretical Background", 1988. Lamei, Saleh and others, "Dar AI-Aytam complex, Old City of Jerusalem Case study on Photogrammetric Recording", 2000-2001. Venice charter, 1964. Weaver, Marin E, "Conserving Buildings -a Manual of Techniques and Materials", Preservation Press, 1997. http://epubl.ltu.se/1402-1544/2006/02ILTU-DT-0602-SE.pdf, koh, Yang Sook, "Laser Cleaning as a Conservation Technique for Corroded Metal Artifacts", 2005. (Accessed 2/4/2006). http://www.lems.brown.edulvote/photogrammetry index.html, "Photogrammetric Digital Reconstruction in ArchaeologyThe Great Temple at Petra, Jordan", (accessed 5/412006). http://siba3:unile.itlctte/3ddb/silkroad/silkroad-paper.pdf, Taylor, J.M and others, "Applications of high-resolution 3D Imaging to the Recording and Conservation of Ancient Crypt and Grotto Sites", 2004. (Accessed 6/412006). http://www.cs.kent.ac.uk!people/staff/nsrlarchlvisrcantlvisircant. html, "Visualising Roman Canterbury: Computer Graphics in Archaeology", last updated: 20th January 1997. (Accessed 6/412006).

11-

http://www.liverpoolmuseums.org.uk!conservationltechnologiesl 3drecording p2.asp, "Conservation Technologies, 3D recording 1 3D scanning - the applications". (Accessed 5/412006). 12- http://www.univie.ac.atiLuftbildarchiv/wgv/intro.htm. "Introduction to Photogrammetry". (Accessed 27/3/2006). 13- http://cipa.icomos.org/fileadminlpapers/antalya/41.pdf, Karsli.F, Ayhan.E, Tunc.E, "Building 3d photo-texture model integrated with GIS for architectural heritage conservation". (Accessed 17/312006).

SIMULATION OF OPTICAL RESONATORS FOR VERTICAL-CAVITY SURFACE-EMITTING LASERS (VCSEL)

MOHY S. MANSOUR National Institute of laser Enhanced Sciences Cairo University MAHMOUD F. M.HASSEN Higher Institute of Technology, Benha University.

ADEL M. EL-NOZAHEY National Institute oflaser Enhanced Sciences Cairo University

ALAA S. HAFEZ Faculty of Engineering, Alexandria University SAMER F. METRY National Institute oflaser Enhanced Sciences Cairo University

Simulation and modeling of the reflectivity and transmissivity of the multilayer DBR of VeSEL, as well as inside the active region quantum well are analyzed using the characteristic matrix method. The electric field intensity distributions inside such vertical-cavity structure are calculated. A software program under MATLAB environment is constructed for the simulation. This study was performed for two specific Bragg wavelengths 980 nm and 370 nm for achieving a resonant periodic gain (RPG)

1. Introduction

Vertical-cavity surface-emitting laser (VeSEL), is a modern semiconductor laser device, with a very promising applications. VeSELs are already being used in short distance data links, free space communications, optical printing, data storage, bar code scanner, instrumentation and medical devices. The VeSEL output beam is normal to the surface of the wafer as shown in Figure 1.

171

172

Figure I.The output beam from VeSEL

Two reflectors known as distributed Bragg reflectors (DBR) that serve to reflect light back and forth across an active region are employed. The active region amplifies the light by stimulation emission [4], [5] and [3] while the DBRs will create a high-finesse Fabry-Perot cavity within which are placed integer multiples of half-wavelength thick (IJ2n) quantum-well active regions [4] and [7]. The DBRs are consisted of repeating pairs of quarter- wavelength thick high and low-refractive index semiconductor layers. By combining the multiple light reflections form quarter-wavelength thick of high-to-low refractive index layers, a maximum reflectance greater than 99 % can be obtain. The materials used for the high and low index semiconductor layers are chosen to maximize their index contrast and yet be transparent to the laser light. The structure of veSEL shown in Figure 2. is a typical device structure that comprises two highly reflective DBRs and with the active region in-between.

173

~ "-'C ontact

>

LLgbtOnt DBA

4-4------

~

AcU,

DBR

N..contact Figure 2. The structure of veSEL

2. Cavity Analysis

2.1 Reflectivity and Transmissivity on DBR. The reflectance R and transmittance T of a multilayer are defined as the ratio of reflected and transmitted optical energies respectively to the incident optical energy. The amplitudes of the reflected and transmitted waves are complex quantities whose argument represents phase change on reflection or transmission by the multilayer [1], [2] and [3]. In this section, calculation for the reflectance as well as transmittance based on characteristic matrix method is presented. The model is based on the following assumptions: 1. The mirrors are half-wavelength apart with Bragg wavelength at 980 nm. 2. The layers have a quarter-wavelength thickness:

= AB

d

4n

(1)

Where AB is Bragg wavelength and n is the refractive index of the layer. 3. The admittance of each layer is given by

'lJ

= nY cos e

(2)

174

Where Y is the optical admittance of vacuum, n is the refractive index, and the incident angle. 4. The path difference phase shift is given by:

tS = 21l11d cos e

e is

(3)

/L Where n is the refractive index, d is the thickness, is the emitted wavelength. The characteristic matrix method is applied, Where

e is the incident angle, and A

(4) n is the layer next to the substrate ,M 1 indicates the matrix associated with layer 1, and so on. Equation 4 can be written as:

-nr~os~ (i sinb)/ TJr][l ] [b]c =~~!L1TJrsmtS costS 1}n

(5)

Where t3 is the phase shift, and 11' is the admittance for layer r. In s-polarization 11m is the substrate admittance and N is the number of layers. 5. Reflectance is given by:

- * -- ('f}oB - C R-pp 'f}oB + C

J( 'f}oB - C J* 'f}oB + C

(6)

Where 110 is the incident medium admittance. 6. Transmittance is given by:

T

4'f}o

'f}m

('f}oB + C)

('f}oB - C) *

(7)

Where 110 is the incident admittance, and 11m is the substrate admittance.

2.2 Resonator Structure In this section, the resonator is in incorporated into the optical multilayer, shown in Figure.3

as

175

Cavily Region

110

...

p-

Cavity length

Figure3. A typical VeSEL structure.

The characteristic matrix of the upper layers, cavity region and bottom layers are combined together to give

MTOTAL = (Mu). (Me). (Mb)

(8)

Where Mu represents the characteristic matrix of the upper layers, Me represents the characteristic matrix of the cavity region and Mb represents the characteristic matrix of the bottom layers.

2.3 Electric Field Intensity Analysis It is a great important for studying electric field intensity inside the multi layers

and the resonator because the absorption of radiation at any point is directly proportional to intensity, thus extra attention must be paid particularly at high intensity region to minimize the possible source of absorption such that lesser current density will be derived. In order to reduce the absorption in the multilayer, the intensity inside the multilayer must be known first. In this section, calculation of field intensity inside a multilayer will be presented. In VeSEL resonators, higher refractive index layers, such as GaAs, will exhibit a higher absorption as compare to lower refractive index, such as AlAs. Due to this reason, GaAs is normally found in the second layer of the resonator.

176

Calculation of field intensity inside a multilayer is performed via a program under MA TLAB environment. In each film interface, light is separated into a series of reflected and transmitted beams. Therefore, by obtaining the reflected and transmitted beams, the resultant electric field at anyone point inside the multilayer can be determined. Figure 4. Illustrates the concept of calculating the electric field inside a multilayer.

x 11

c i d

SubsLmte

zl ............. ,...z

ZN+I

e -4------------~------------~~----~----~z

Rj

n

dj Inter.lace

J

I I1terillce j Figure 4. Notation for field intensity calculations.

The positive and negative going electromagnetic wave at some point z, where Z is more than Zj but less than Zj+h in the jth layer are related to the amplitude reflection and transmission coefficients at the interfaces of that layer by the following Eq. (11): Ei+ (2) = To; exp{ [-2I1in, (Z - Z; )cosa]/ A}

(9)

1- R;oR;,N+l[(--4I1;n;d; cosa)/ A]

Ei'"(Z)

R;,N+l~; exp{grJin,(Z-Z; -d; )cosB;]/ A}

(10)

1-R;oR;,N+l[(-4I1;nA cosB;)/ A] where Toj is the amplitude transmission coefficient for radiation of wavelength A traveling from the medium of incidence to the jth layer, measured in the jth layer at the jth interface, Rjo is the amplitude reflection coefficient for layer 1 to interface j -1, measured in the jth layer at the jth Interface , RjN+1 is the amplitude reflection coefficient for interface j + 1 to the substrate measured at

177

the (j + I)th interface inside the jth layer; nj and OJ are the refractive index and the incident angle for thaJ particular layer j when calculating transmission and reflection coefficient; A is the Bragg wavelength and dj is the thickness of layer j. The equation for amplitude transmission coefficient, Taj, is similar to Eq. (6).

2lJo lJoB+ C

TOi

(11)

3. Results and Discussions The reflectivity, transmissivity and the distribution of the electric field intensity in multilayer and the resonator are simulated through a software program under MATLAB environment. All results are based on the following values: ni = 1, nI(AlAs)= 2.92, n2(AlN)= 2.21, n substrate (GaN) =2.74, Oi = 0°, AB =980 nm.

3.1 The Reflectivity and Transmissivity jor DBR Layers. As shown in figures 5 and 6 the reflectivity and transmissivity have been calculated for number of layers equal to 10, 15, 20 and 25. Reflectivity vs Wavelength

1

v/

N~~f layers=1 0 No of layers=15 No of I aye rs=20 No of layers=25

.-----

0.8

.g ____ ____ ---:>-.

0.6

:

--

{'::

:

]--4. L--------;------- i ~A -----0::

0.4

0.2

I'

J:/ \':'~

h '/~ -~~ :---------~ ------- t: V:·ll: : ~'l::, ;.. :l l::~: : 'i q \ ~ i \j ~~---------t------- ~ti 11l~---,.fl' "1

':

'

1- ' - - -

y ~\ ~ ;

goo

: ~ L~' ~

;

900 1 000 1 1 00 Wavelength (nm)

Figure 5 -a. reflectivity versus wavelength at

Ag

=980nm

I

1200

178

Reflectivity vs Wavelength

0.9

,------------+-----------~------------.-----I

I

I

I

O.B 0.7

0.6

~------------.------------I------------.------I I I I

, : Wavelength: (nm) 0.5wu--------L-------~------~----~

900

950

1000

1050

Figure 5-b. zoom for Figure 5 -a. Transmissivity vs Wavelength

0.9 0.8 0.7

r -,

-

• _______ L • •

j

______

~

•

______

J

I

___ _

··

.

: : -: •.•..•

No of layers =10 No of layers =15 No of layers =20

• •

I •

. I I

,

.

0.6

I •

i;; -~ ! :-af wav~re-ngth~9BITnm~- ---

------r- ~ i ------..:---~ : :..

0.5 0.4 0.3

------'1-----

0.2 0.1

BOO

850

900

950

1000 1050 1100 Wavelength (nm)

Figure 6. Transmissivity versus wavelength at

1150

1200

0

Ag =98Onm

From figures 5(a) and 5(b) and 7(a) and 7(b) it is noted that: 1. The higher numbers of layers are the higher reflectivity and lower transmissivity. 2 .The spectral widths is inversely proportional to the numbers of layers. 3. The amplitude of the first side loop is directly proportional to the number of layers.

179

4. The spectral width is inversely proportional to the number of side loops. By repeating the above analyses with a different wave length A =370nm, the variation of reflectivity with wavelength is shown in figures 7-a and 7-b. Reflectivity vs Wavelength

0.8

.

~ <>

~.

0.6 - - ===-. - - - - - - - - - - - - -:- ~

.""!:::::::

I

:>

"-B
=

.

0.4

--~----,--------

0.2

-------

0::

~oo

200

300

400

Wavelength (nm)

500

Figure 7-a. reflectivity verses wavelength at

600

Ag

=370nm

Reflectivity vs Wavelength

0.95

0.9

----J--------

c: - - - - - -,.."""' .:

-~:.. :'!::::::

...

·

. .....

··· ···· ·..

.... ... ....

-----:-----

.

--------~--------~-------

•

"uw ':

0.85

·· ··· ··

--------~--------~-------

-~-~------

--------~--------~-------

~:

··· · ····

0.8

..

.. ..

~--------r--------r-------

·

O.75L-~~--~~·~--~~~--~~·~--~~~~~~--~

320

40

360

380

400

420

Wavelength (nm)

Figure 7-b. zoom for Figure 7-a.

As shown in figure 7 the spectral width at wavelength A = 370 nm is narrower than the spectral width at wavelength A = 980 nm. This means that, from the

180

study of the reflectivity and transmissivity on the DBR layers, the spectral width for lower wavelengths is narrower than the higher wavelengths. To achieve the optimum conditions for the VeSEL design, it is necessary to determine 1. Minimal numbers of layers. 2. Smaller numbers of side loops. 3. Lower value for the first side loop. 4-Acceptable spectral width It is clear to not that from the figures 5 and 7 that at number of layers of 10 the reflectivity=99.6% and the transmissivity=0.04% while at number of layers =15, 20 and 25 the reflectivity=100% the transmissivity = 0.000%. That is the reflectivity and the transmissivity reach to the saturation value when the number of layers is 10 and there is no benefit from increasing numbers of layers. On the other hand, it is very useful to decrease the numbers of layers to decrease the threshold current and so to reduce power consumption and to reduce the thermal effect on the device.

3.2 The Reflectivity and Transmissivity jor Optical Resonator For VeSEL cavity resonator consisting of upper DBR mirror with number of layers 10 and lower DBR mirror with number of layers 10, and an active medium with index of refraction n cavity =2.3, the reflectivity and transmissivity are evaluated and shown in figures 8 and 9. Reflectivity vs Wavelength

f:

,

-_1,________ - ... - _________

0.8

~_

,, ,

~

~.6

-

·A ----

.<:: W (])

, ----------j,

,, -----------

-

---1--------

- - t - _ _ _ _ _ _ _ _ _ ... _

,,

II

'0)0.4 0::

0.2 --

,,,

,,, ,,

- - -!,, - - - - - - - - - - - - - - - - - - ~ - ,,

------

OL--...1----L_'--_ _-"--'--_ _ _.l..--....L-_----'

800

900

1000

1100

1200

Wavelenqth (nm)

Figure 8.Reflectivity versus wavelength at

Ag

= 980 nrn for the VeSEL cavity resonator.

181

From figure 8 the reflectivity in the resonator at wavelength AB =980nm has a minimum value. Transmissivity vs Wavelength .2 r--------,---------,--------,---------,

- - -:- -

-

- - - - -

-i----------: -

-------

~

°:>-,0.8

.= .

""

(f) (f)

u ------

·~0.6

= ""

.=

0.4

0.2

---!v---

----v -j:

go~o~----~g~O~O~----~1~O~O~O~-----1~1~O~O~-----1~2~OO Wavelength (nm)

Figure 9. Transmissivity versus wavelength at

Ag

=980nm for the VeSEL cavity resonator.

3.3 The Electric Field Intensity for Multilayer and Active Region It is very important to study the electric field intensity inside layers and active

region for analyzing the relationship between the electric filed intensity and the type of the material where the type of material is related to the refractive index of the layer. In addition, to determine exactly where the peak of the electric field intensity is located inside active region for achieving resonant period gain (RPG).

3.3.1 The Electric Field Intensity for Multilayer The electric field intensities calculated from equations 9 and 10 are shown in figure 10. There are two plotting curves the gray one represents the smaller values of refractive index of layers nl = 2.92, n2 = 2.21, and nsub = 2.74 And the black one represents the higher values of refractive index of layers nl = 3.5, n2 = 2.92, and nsub = 2.74. It is noted that the value of the refractive index for the layer is inversely proportional to electric field intensity. This result is very useful for VeSEL design because the derived current is related to the electric field intensity and this is very important for reducing the threshold current.

182 Electric Field Intensity Distribution

1 .2

- - - - - - - , - - - - - - - -

- 1

:z -

t--+----- pel

--A- ---~ ----" --

1

0.8

,_ l I

".....

'1;:i

~0.6

n1 =2 ~2.n2=2.21 n~ ub=2.74 n1 =315.n2=2.92. S l b=2.74

J

"E

0.4

0.:

~-

-- -l--------

---.JlV~V~_.J!~~~~~i1~j~:Y..--.~&--.s.~

-J.".-...L..--_----1-

[)LV

o

0.5 1.5 2 Distance from Reference Interface (urn)

2.5

Figure 10. The electric field intensity for multilayer for different refractive index

3.3.2 The Electric Field Intensity for Resonator. For the best design to VeSEL a great attention must be bayed for achieving RPG, this means that placing gain media at successive peaks of the standing optical wave inside a multi-wavelength cavity as shown in Figure 11.

quantum wells

~

/ .

mirrors /~

Figure II. Conventional half-A VCSEL cavity (left) and 3/2 A VCSEL cavity (right)

183

For achieving RPG we have to study the electric field intensity inside the resonator at different wavelengths as shown in figure 11 and study the shift in the distance between the two wavelengths and so we can correctly determine where to place the active region in the VeSEL.

Electric Field Intensity Distribution

1.4

-

---

1.2

----,,----------

vvave len gt h=370 n m vvave len gt h=9S0 n m -------------

· ·

1 O.S

0.6

-------------

0.4 0.2

o 100 200 300 Distance from Reference Interface (urn) Figure 12. The electric field intensity for

Ag

=370nm,

Ag

=980nm

As shown in figure 12 shows the electric field intensity inside VeSEL. It can be observed that strong electric field intensity occurred in the resonator and the electric field intensity starts to diminish after it has passed the resonator region. An also appear that is shift in distance between the two wavelengths. From this information, we can correctly determine where to place the active region in the nitride VeSEL. 4. Conclusions It can also be seen that by simply adjusting the number of DBR layers, it will

significantly affect the overall reflectivity as well as transmissivity. Moreover, it can be noted that by selecting the optimum values of first layer refractive index, second layer refractive index , substrate refractive index we have a minimal numbers of layers for VeSEL construction and so enhancing the threshold current density and so reducing the power consumption that needed for lazing and decries the thermal effect on the device . Determining the electric field intensity for different wavelength by applying RPG inside active region for determining correctly where to place the active region in the VeSEL due to the shift in the distance between the two wavelengths.

184

References 1. Tey Wee Khiang Ace, "Design of resonators for Vertical-Cavity SurfaceEmitting Lasers".Department of Computer Science and Electrical Engineering The University of Queensland.

2. Wee Khiang Ace Tey , "Design of low threshold Vertical-Cavity SurfaceEmitting Lasers, Department of Computer Science and Electrical Engineering The University of Queensland. 3. David Wells Winston, "Physical simulation of optoelectronic semiconductor devices".David W. Winston, Member, IEEE, and Russell E. Hayes, Member, IEEE Journal Of Quantum Electronics, 34, 4, (1998) 4. Trevor Fong Siu Kae, " simulation of Vertical-Cavity Surface-Emitting Lasers IEEE Journal Of Quantum Electronics, 34, 4, (1998) 5. Renaud Stevns, "Modulation properties of Vertical-Cavity Surface-Emitting Lasers". 6. David W. Winston, "Optoelectronic Device Simulation of Bragg Reflectors and Their Influence on Surface-Emitting Laser Characteristics", IEEE Journal Of Quantum Electronics, 34, 4, (1998) 7. Kenichi Iga, "Multi-Oxide Layer Structure for Single-Mode Operation in Vertical-Cavity Surface-Emitting Lasers", IEEE Photonics Technology Letters, 12,6, (2000). 8. "VCSELs go the distance", Optic photonic news (2002). 9. P.Maaekowlak, T.Czyszanowski, R.P.Sarzaea, M.Wasiak and W.Nakwaski " Designing of possible structures of nitride Vertical-Cavity Surface-Emitting Lasers," Opto-electronic Review 11(2),119-126 (200310). 1O.Harry J. R. Dutton" Understanding Optical Communications" International Technical Support Organization, September 1998 http://www.redbooks.ibm.com

OPTICAL DESIGN ALTERNATIVES: A SURVEY STUDY A YMAN ABDEL KHADER ISMAIL, PROF. IMANE AL Y SAROIT ISMAIL AND PROF. S. H. AHMED

Information Technology Department, Faculty of Computers & Information, Cairo University Computers have enhanced human life to a great extent. Our daily lives demand solutions to increasingly sophisticated and complex problems, which requires more speed and better performance of computers. Although the development of the Very Large Scale Integration (VLSI) technology with smaller device dimensions and greater complexity and speed but it does not permits the demand of faster and enhanced computers. Because of the advantages of optical transmission over electronic ones most of researches focused on optical circuit design. In the recent few years, many studies were published in this field. In this paper we will review different methods of optical digital design.

1. Introduction Computers have enhanced human life to a great extent. The speed of conventional computers is achieved by miniaturizing electronic components to a very small micron-size scale so that those electrons need to travel only very short distances within a very short time. The goal of improving computer speed has resulted in the development of the Very Large Scale Integration (VLSI) technology with smaller device dimensions and greater complexity. Additionally, our daily lives demand solutions to increasingly sophisticated and complex problems, which requires more speed and better performance of computers. For these reasons, it is unfortunate that VLSI technology is approaching its fundamental limits in the sub-micron miniaturization process [1]. Optical interconnections and optical integrated circuits will provide a way out of these limitations to computational speed and complexity inherent in conventional electronics. Optical computers will use photons traveling on optical fibers or thin films instead of electrons to perform the appropriate functions. In the optical computer of the future, electronic circuits and wires will be replaced by a few optical fibers and films, making the systems more efficient with no interference, more cost effective, lighter and more compact[l]. Optical components would not need to have insulators as those needed between electronic components because they don't experience cross talk. Indeed, multiple

185

186

frequencies (or different colors) of light can travel through optical components without interfering with each others, allowing photonic devices to process multiple streams of data simultaneously. Optical interconnections and optical integrated circuits have several advantageous over their electronic counterparts. They are immune to electromagnetic interference, and free from electrical short circuits. They have low-loss transmission and provide large bandwidth; i.e. multiplexing capability, capable of communicating several channels in parallel without interference. They are capable of propagating signals within the same or adjacent fibers with essentially no interference or cross-talk. They are compact, lightweight, and inexpensive to manufacture, and more facile with stored information than magnetic materials [2]. Most of the components that are currently in use with very much in demand are electro-optical (EO). Such hybrid components are limited by the speed of their electronic parts. All-optical components will have the advantage of speed over EO components. Unfortunately, there is an absence of known efficient nonlinear optical materials that can respond at low power levels. Most nonlinear optical components require a high level of laser power to function as required. A group of researchers from the University of Southern California, jointly with a team from the University of Los Anglos, have developed an organic polymer with a switching frequency of 60 GHz [1,2]. On other side of view; the future Internet will rely on optical routers without the need for any optoelectronic conversion. Although optical technologies are playing increasingly important roles in wide and local area networks, current optical network elements still offer limited functionality compared to their electronic counterparts. All-optical digital processing is an exciting area of research towards finding new ways to process and transmit information entirely in the optical domain. Optical technology has distinct advantages in the area of transmission of information, e.g. massive bandwidth, absence of electromagnetic interference, and low power consumption [4]. Though, Optics has a higher bandwidth capacity over electronics, which enables more information to be carried and data to be processed arises because electronic communication along wires requires charging of a capacitor that depends on length. In contrast, optical signals in optical fibers, optical integrated circuits, and free space do not have to charge a capacitor and are therefore faster. Another advantage of optical methods over electronic ones for computing is that optical data processing can be done much easier and less expensive in parallel than can be done in electronics. Parallelism is the capability of the system to execute more than one operation simultaneously [5].

187

Another advantage of light results because photons are uncharged and do not interact with one another as readily as electrons. Consequently, light beams may pass through one another in full duplex operation, for example without distorting the information carried. In the case of electronics, loops usually generate noise voltage spikes whenever the electromagnetic fields through the loop changes. Further, high frequency or fast switching pulses will cause interference in neighboring wires. Signals in adjacent fibers or in optical integrated channels do not affect one another nor do they pick up noise due to loops. Finally, optical materials possess superior storage density and accessibility over magnetic materials. [2,3,5].

2. Optical Design

2.1. Metallic Based Design The reflectance and transmittance of thin films exhibit strong polarization effects (PEs), particularly for the films inside a glass cube, which result from the fact that the tangential components of the electric and magnetic fields are continuous across each layer interface. This property has been employed in the design of polarizer. However, for some applications it is undesirable and should be reduced. Therefore, the concept and its design methods of non-polarizing beam splitters (NPBSs) are proposed and reported in some literatures. Costich, reported two methods to reduce the PEs in interference films, in 1970, especially in metal-dielectric filters and beam splitters with one air interface. Generally, thin films have strong polarization effects (PEs) at oblique angles of incidence. A possible way to solve the problems induced by the reflection-induced retarding is to coat polarization-preserving medium layers on the reflecting surface of the device when the PEs are not desirable [3].

2.1.1.

Infrared Beam Splitter

Zheng et al. [16], introduce two designs of a ZF-7 or K9 glass cube, which bases on quarter-wave layers at reference wavelength A. = 1300nm and the angle of incidence e = 45°, show 50% reflectance and 50% transmittance for both polarization states at A. with the measuring error less than 10% and small reflection-induced retarding. For materials Nd203, Al203 and MgF2, a 14 layers quarter wave stack with alternating high and middle index layers is constructed on the substrate. Then a six layers quarter wave stack with alternating low index and middle index layers is added to the previous stack. It shown that the values of reflectance of p polarization and s polarization at A. = 1300 nm are 50% and 50%, respectively, and the reflection induced retarding is

188

close to zero and reflection induced retarding in the vicinity is very low. For materials ZnS, Si02 and MgF2, respectively, that the values of the reflectance of p polarization and s polarization at A. = 1300 nm are 43% and 47%, respectively, and the reflection-induced retarding is close to zero [16]. 2.1.2. Holographic Optical Element Yasuhiro et al. [15] suggest a design and fabricate of an optimum holographic optical element (HOE) lens for a femtosecond laser. They design and analyze a HOE lens illuminated with a femtosecond laser pulse. This HOE lens for a laser pulse has 130 fs duration, nOnm central wavelength, and lOnm spectrum bandwidth. The HOE lens gives both high diffraction efficiency and small amount of aberration. The designed HOE lens is fabricated and its optical characteristics have been experimentally evaluated. The reconstructed point images agree with the results of the numerical simulations of the capability of designing the optimum HOE lens for a femtosecond laser pulse [15]. 2.1.3. Diffractive Optical Elements Xiao et al. [14], Design a diffractive optical elements (DOEs) for implementing spatial demultiplexing and spectral synthesizing simultaneously, by using conjugate gradient optimization algorithm. Three different design cases for the spectrum window of the optical communication: three discrete spectral segments in one direction, two discrete spectral segments in two directions, and three discrete spectral segments in three directions, are implemented. The numerical simulations indicate that the designed multi-functional DOEs can successfully generate desired spectra at pre-designed directions. These designs can provide useful information for designing the wavelength division multiplexer and the arrayed waveguide grating in various optical systems [14].

2.2. Organic Based Design The photochromic protein bacteriorhodopsin (bR) contained in the purple membrane fragments of Halobacterium halobium, has emerged as an excellent material for bio-molecular photonic applications due to its unique advantages. It exhibits high quantum efficiency of converting light into a state change, large absorption cross section and nonlinearities, robustness to degeneration by environmental perturbations, high stability towards photo-degradation and temperature, response in the visible spectrum, low production cost, environmental friendliness, capability to form thin films in polymers and gels and flexibility to tune its kinetic and spectral properties by genetic engineering techniques, for device applications. By absorbing green-yellow light, the wild type bR molecule undergoes several structural transformations in a complex photocycle that generates a number of intermediate states. The main photocycle

189

of bR is as shown in Fig. 1. After excitation with green-yellow light at 570 nm, the molecules in the initial B state get transformed into J state with in about 0.5 ps. The species in the J state thermally transforms in 3 ps into the intermediate K state which in turn transforms in about 2 Ils into the L state. From the L state bR thermally relaxes to the MI state within 8 IlS and undergoes irreversible transition to the MIl state. The molecules then relax through the Nand 0 intermediates to the initial B state within about 10 ms. An important feature of all the intermediate states is their ability to be photo-chemically switched back to the initial B state by shining light at a wavelength that corresponds to the absorption peak of the intermediate in question. The wavelength in nm of the absorption peak of each species is shown as a subscript in Figure 1 [9].

Figure I Schematic of the photochemical cycle of bR molecule.

2.3. Organ Metallic Based Design 2.3.1. Spatial light modulation Serge et al. [7], present a general theoretical analysis of all-optical spatial light modulation in organometallic compounds based on nonlinear excited-state absorption, considering the propagation effects of both read and write beams. A detailed analysis for Ptethynyl complex has been presented based on the rate equation approach and an analytical solution for the write beam transmission has been obtained. For typical values, the read beam at 633 nm is modulated by 97.9% with a write beam intensity of 100 kW/cm2 at 355 nm. It is shown that the effect of write beam propagation in the medium is appreciable at low write beam intensities and the percentage modulation in Ptethynyl complex is larger than that in C60 in toluene and Zn. Spatial light modulation has been analyzed by considering the transmission of a cw read laser beam at 633 nm that corresponds

190

to the He-Ne laser wavelength, through Ptethynyl complex, which is modulated by a cw write laser beam at 355 nm that corresponds to the maximum ground state absorption. A schematic diagram of all-optical light modulation of read beam by a write beam in the nonlinear medium is as shown in figure 3 [7].

I .... ,

x

Figure 3 Schematic diagram of all-optical spatial light modulator [7].

2.3.2.

Ptethynyl Thin Film

Singh et al. [8], Introduce a thin film of Ptethynyl complex exposed to a light beam of intensity I, which modulates the population densities of different states through the excitation and de-excitation processes. A schematic diagram of all optical switching of a cw probe beam by a pulsed pump laser beam in the nonlinear medium is as shown in figure 4. These light-induced population changes can be described by the rate equations in terms of the photo-induced and thermal transitions of different levels [8]. Pt:othynylsamplo

ow _

..-

"L----:-::-= 'V ~

63anm~

J\:

"L

T...... mlbd probe bNm

PulMd pwnp bNm 355nm

Fig. 4. Schematic diagram of all-optical switching [3].

2.3.3.

All-Optical Switching Polymethine Dye

Prag et al. [5], investigate Polymethine dye(2-[2-[3-[(1,3-dihydro-3,3-dimethylI-phenyl-2H-indol-2-lidene)ethyline]-2-phenyl-l-cyclohexene-l-yl] ethenyl]3,3-dimethyl-l-henylindolium perchlorate) (PD3) that exhibits large excitedstate absorption, using the rate equation approach, to achieve high contrast and fast switching. The transmission of a cw probe laser beam (I) at 532 nm through

191

PD3 dissolved in (i) ethanol and (ii) polyurethane acrylate (PUA), is switched by a pulsed pump laser beam at 532 and 650 nm, respectively, which excite molecules from the ground state. The theoretical results show good agreement with the reported experimental results for case (i). The switching characteristics have been shown to be sensitive to variation in concentration, pump pulse width, peak pumping intensity and absorption cross-section of the excited-state at 532 nm and lifetime of excited-state. The same switching contrast can be achieved at relatively lower pump powers intensity at 650 nm for case (ii). It is shown that there is an optimum value of concentration at which maximum modulation can be achieved. A 96% modulation of intensity at 650 nm, with t=30 ps and concentration of 0.14 mm in PU A, resulting in switch OFF and ON time of 95 ps and 18 ns, respectively [5].

2.3.4. Phthalocyanine and Polydiacetylene Switching Abdeldayem et al. [1]; Recently in NASAlMarshall Space Flight Center demonstrated two fast all-optical switches using phthalocyanine thin films and polydiacetylene fiber. The phthalocyanine switch is in the nanosecond regime and functions as an all-optical AND logic gate, Fig. 5, while the polydiacetylene one is in the picosecond regime and exhibits a partial all-optical NAND logic gate [1] . Nanosecond All-Optical AND-logic Gate

Figure 5 A schematic of the nanosecond all-optical AND [I).

To demonstrate the AND gate in the phthalocyanine film, they waveguided two focused collinear beams through a thin film of metal-free phthalocyanine film. The film thickness was - 1 mm and a few millimeters in length. Then using the second harmonic at 532 nm from a pulsed Nd:Y AG laser with pulse duration of 8 ns a long with a cw He-Ne beam at 632.8 nm. The two collinear beams were then focused by a microscopic objective and sent through the phthalocyanine film. At the output a narrow band filter was set to block the 532 nm beam and

192

allow only the He-Ne beam. The transmitted beam was then focused on a fast photo-detector and to a 500 MHz oscilloscope. It was found that the transmitted He-Ne cw beam was pulsating with a nanosecond duration and in synchronous with the input Nd:YAG nanosecond pulse. A schematic of the setup is shown in Fig. 5. The setup for the picosecond switch was very much similar to the setup in Fig. 5 except that the phthalocyanine film was replaced by a hollow fiber filled with a polydiacetylene. The polydiacetylene fiber was prepared by injecting a diacetylene monomer into the hollow fiber and polymerizing it by UV lamps. A fast detector was attached to the monochrometer and sending the signal to a 20 GHz digital oscilloscope. It was found that with the He-Ne beam OFF, the Nd:YAG pulse is inducing a week fluorescent picosecond signal (40 ps) at 632.8 nm that is shown as a picosecond pulse on the oscilloscope. This signal disappears each time the He-Ne beam is turned on. These results exhibit a picosecond respond in the system and demonstrated three of the four characteristics of a NAND logic gate as shown in Fig. 6 [1]. Nano and Picosecond AII-optical Switch

Fig. 6. A schematic of the all-optical NAND logic gate setup [1].

2.4.

Semiconductor Optical Amplifier (SOA) Based Design

2.4.1. NAND Gate Design

An all-optical NAND gate using integrated semiconductor optical amplifier SOA-based Mach-Zehnder interferometer is proposed by Xiaohua et al. [14]. The proposed NAND gate is synchronous with the dynamic gain experienced by the probe pUlses. The effects of the SOA and input data parameters on the switching performance are discussed. The operation of the proposed NAND gate with 10 Gb/s RZ pseudorandom bit sequences is simulated and the results demonstrate its effectiveness.

193

o

C2 \ . . P o rt 2

h h" " In.pu t O ... t... B

Fig. 7. Schematic diagram of all-optical NAND gate using SOA-MZI [14].

This NAND gate could provide a new possibility for all-optical routing in future all-optical networks. In future high-speed optical label-switched networks, optical label will require rapid routing at all-optical switches to avoid cumbersome and power-consuming OfE/O conversion. In transmission, the optical label has to be examined at each node to retrieve the destination information, which is essential for making routing decision [14]. At the output of MZI, the probe signals in both arms interfere either constructively or destructively through coupler C3 depending on the differential phase-shift between two probe pulses, i.e., the input control data determine the phase-shift experienced by the probe pulses, so as to influence the output signal of MZI. When data A and data B are "1 ," the control-signals from ports 3 and 4 are identical. Due to the XPM, the differential phase-shift is close to 0, thus the output of MZI becomes O. In the other cases, the control data from ports 3 and 4 are different, which results in the generation of a pulse at the wavelength of the probe pulses and the output of MZI becomes 1, therefore the logic truth table is achieved [14].

2.4.2. OR Gate Design Wang et al. [11], demonstrated All-optical OR operation using a semiconductor optical amplifier (SOA) and delayed interferometer CD I) at 80 Gb/s. The DI is based on a polarization maintaining loop mirror. Q-factor of the operation is discussed through numerical simulations. The results show the OR gate operation rate is limited by the gain recovery time and input pulse energy. For high-speed optical communication networks, logic operation is important for networking functions, such as switching, signal regeneration, addressing, header recognition, data encoding and encryption, etc.

194

-,V

=~r---------:.'," .~: Cr:c",.: o-

-~ booWw

rC'

-+-SOA·DI realind using polarization maintaining fiber (PMF)

""'.

Fig. 8. Experimental setup for the OR function demonstration [IIJ.

The technique based on SOA-DI devices has the advantage over Mach-Zehnder devices in that it requires one SOA and hence it operates at lower power. The simulation shows the data rate limitation is set by the gain recovery time of the SOA. The OR gate operation is based on the gain saturation and phase modulation of optical signals in the SOA. The schematic diagram of the principle is shown in Fig. 8, The signals A and B and a CW control signal (which would carry the information of OR output) are injected into the SOA, the data signals A and B induce phase shifts to the CW signal via cross-phase modulation in the SOA [11]. The CW signal carrying the time dependent phase shifts is injected into a polarization maintaining loop (PML) mirror, which serves as a delayed interferometer. The input CW signal is polarized along either the fast or the slow axis of the polarization maintaining fiber in the loop prior to injection into the PML. The CW signal splits and propagates in the PML as a clockwise component and a counter clockwise component. -

I nput 1 , 1 010

Input 2 ,1 000 -

Output , 101 0

T im e (pa)

Fig. 9. Experimental result of SOA OR operation [IIJ .

The in-loop polarization controller (which is near the coupler) is adjusted so that it rotates the polarization by 90. Thus, the clockwise component and the counter clockwise component of the light in the PML are polarized along the two optical

195

axis of the polarization preserving fiber. Since the optical path is birefringent, the phase difference between the pulses with polarization along the fast and slow axis accumulates and results in a differential phase delay of kO, where kO is the wave vector in the vacuum, Dn is the difference in index seen by the light propagating along the fast and slow axis, and L is the fiber length in the PML. The clockwise and counter clockwise components traverse the in-loop polarization controller once and arrive at the coupler with the same polarization where they interfere [11]. References 1.

Abdeldayem Hossin, Donald O. Frazier, Mark S. Paley, and William K. Witherow, "Photonic Devices for Optical Computing" ,NASA Marshall Space Flight Center, Space Sciences Laboratory, Huntsville, a135812. 2. Kato A., Oishi S., Shishido T., T. Yamazaki T., Iida S., "Evaluation of stoichiometric rare-earth molybdate and tungstate compounds as laser materials", Journal of Physics and Chemistry of Solids 66 (2005) pp.20792081. 3. Liua W.L.,_, Xiab H.R., Wangb X.Q., Lingb Z.c., Ranb D.G., Xuc J., Weic Y.L., Liua Y.K., Sunb S.Q., Han H., "Characterization of deuterated potassium dihydrogen phosphate single crystals grown by circulating method", Journal of Crystal Growth 293 (2006) pp.387-393. 4. Nandigana Krishna Mohan, Quazi T. Islam, "Design of an off-axis HOE light concentrator to focus light from multiple directions in a plane" , Science Direct, Optics and Lasers in Engineering 44, (2006), pp943-953. 5. Parag Sharma, Sukhdev Roy, c.P. Singh, "Dynamics of all-optical switching in polymethine dye molecules", Science Direct, Thin Solid Films 477, (2005), pp42- 47. 6. Richard Scheps, "Upconversion Laser Processes", SSDI:0071727, frog. Quanr. Elecrr. 1996. Yol. 20. No. 4 pp.271-358,Published by Elsevier Science Ltd, Printed in Great Britain. 7. Serge Gauvin, Joseph Zyss, "Growth of organic crystalline thin films, their optical characterization and application to non-linear optics", Journal of Crystal Growth 166 (1996) pp.507-527 8. Singh C.P., Kapil Kulshrestha, Sukhdev Roy, "High-contrast all-optical switching with Ptethynyl complex", Optics, ww.sciencedirect.com. 9. Singh C.P., Sukhdev Roy, "All-optical logic gates with bacteriorhodopsin", Science Direct, Current Applied Physics 3, (2003), pp163-169. 10. Stefan A. Amarande, Michael J. Damzen, "Measurement of the thermal lens of grazing-incidence diode-pumped Nd:YY04 laser amplifier", Optics Communications 265 (2006) pp.306-313.

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11. Wang Q., Dong H., Zhu G., Sun H., Jaques J., Piccirilli A.B., Dutta N.K., "All-optical logic OR gate using SOA and delayed interferometer", Optics Communications 260 (2006) pp.81-86 12. Wong W.M., Blow K.J., "Design and analysis of an all-optical processor for modular arithmetic", Optics Communications (2006) 13. Xiao dong Sun, Juan Liu, Yi-quan Wang, Bo Zhang, Bin Hu, Si Di, Shang Wang, "Diffractive optical elements for implementing spatial simultaneously", Optics demultiplexingand spectral synthesizing Communications (2006) 14. Xiaohua Ye, Peida Ye, Min Zhang, "All-optical NAND gate using integrated SOA-based Mach-Zehnder interferometer", Optical Fiber Technology, www.ScienceDirect.com. 15. Yasuhiro Awatsuji, Yuu Shiuchi,Aya Komatsu, Toshihiro Kubota, "Design and fabrication of an Optimum holographic optical element lens for a femtosecond laser pulse using a hologram computer-aided design tool ", Optics and Lasers in Engineering 44 (2006) 975-990. 16. Zheng Ping WanR-, Jin Hui Shi, Shun Ling Ruan, "Designs of infrared nonpolarizing beam splitters", Optics & Laser Technology 39 (2006) pp.394399.

MATERIALS FOR DIGITAL OPTICAL DESIGN; A SURVEY STUDY A YMAN ABDEL KHADER ISMAIL, PROF. IMANE AL Y SAROIT ISMAIL AND PROF. S.H.AHMED Information Technology Department, Faculty of Computers & Information, Cairo University

In the last few years digital optical design had major attention in research fields. Many researches were published in the fields of optical materials, instruments, circuit design and devices. This is considered to be the most multidisciplinary field and requires for its success collaborative efforts of many disciplines, ranging from device and optical engineers to computer architects, chemists, material scientists, and optical physicists. In this study we will introduce a survey of the latest papers in the field of optical materials and its properties for light; this paper is organized in three major sections, optical glasses, compound materials and nonlinear absorption (multi photon absorption) and upconversion.

1. Introduction

Optical materials are classified according to properties of light they support. Some materials have a high reflection to a wide range of light frequencies, others has high transmission rate, others have the ability to radiate light according to single or multi-photon absorption and some according to frequencies rang of operation. The role of nonlinear materials in optical computing has become extremely significant. Nonlinear materials are those, which interact with light and modulate its properties. For example, some materials can change the color of light from being unseen in the infrared region of the color spectrum to a green color where it is easily seen in the visible region of the spectrum. Several of the optical computer components require efficient nonlinear materials for their operation [1]. The semiconductor silicon (Si) is an element with 14 electrons surrounding the positively-charged nucleus. Silicon has the property that it is transparent to low energy in the infrared portion of the spectrum but it is opaque to photons in the visible portion of the spectrum. This transparency of silicon to the infrared (IR) is a property of the manner in which the atoms are bonded together; in this case, covalent bonds. Covalent bonding between two silicon atoms is visualized as a sharing of electrons supplied by both atoms. The bond comes about because

197

198

shared electrons orbit around both atoms. This overlap of the bonding orbits lowers the energy of the system. For the purpose of bonding, the atoms of silicon may be visualized as having 10 inner, closed-shell electrons (which do not participate in bonding), and four outer electrons that do. When a silicon atom is brought together with four other silicon atoms Figure 1, it shares its four outer electrons (heavy, curved lines in Figure 2) with each of the four atoms. These atoms, in turn, share one of their four outer electrons (light, curved lines) with the central Si atom [2].

Figure 1 Covalent bonding between silicon atoms.

Figure 2 Two-dimensional representation of the silicon lattice.

Covalent bonds are quite directional (the four electrons are arranged symmetrically) as illustrated figure 2 is a two-dimensional representation of the silicon lattice. The covalent bonds are shown by the curved lines connecting the Si atoms. Although this is a line-and-ball representation, it shows that all the outer or valence electrons are tied up in covalent bonds. The inner 10 electrons are tightly bound (binding energies greater than 100 eV) and the outer four form the covalent bonds. Consequently, there are essentially no free electrons available for charge transport [2]. If we shine light of a fixed energy on the sample, we can break the bonds if the photon energy is greater than the bond energy (about 1.1 eV for Si), which corresponds to the near infrared portion of the spectrum. When a bond is broken, the liberated electron is now free to move within the crystal. The empty site, or hole, left by the escaping electron can be occupied by a nearby electron. Consequently, the hole can also migrate through the crystal by exchanges with the bound electrons. Both electrons and holes can transport charge leading to a current, a photocurrent; figure 3, represents this transportation [2].

If the sample is irradiated with low-energy photons which are not energetic enough to break the covalent bonds, the photons will be transmitted through the sample. So there is no mechanism for the absorption of light as well as no photocurrent. As the energy of the photons is increased, a threshold is reached where the interaction of light with the Si lattice can break the covalent bonds. In

199

Si this occurs at an energy EG of about 1.1 eV, at a wavelength of 1.1 micron. This energy lies in the infrared but close to the visible range figure 4 illustrates the relation between photon energy, transparency and absorption in silicon crystal for light spectrum [2].

Transmi$l.ion ------.... \

\ . Pk()t{)ctlrfcllt

r

\ (In(rarw\

o

o

Figure 3 light absorbing for silicon crystal.

\ \

(Vi5ib~c)

Ea Photon energy Figure 4 the relation between transmission and absorption of light for silicon crystal.

2. Optical Glasses The most common types of glasses used in optics are crown glasses and flint glasses, designations based on their dispersions. These designations are further subdivided by composition and have letter designations and number designations called "glass numbers". Common crown glasses have indices of refraction around 1.5 to 1.6, while extra dense flint glass may have an index as high as 1.75. Lenses of crown and flint glasses are often used in multi-component lenses because of their complementary properties. Table I Example data for glass Types

For example, a strong positive crown lens with its low dispersion may be used in a doublet with a weaker negative lens of flint glass (high dispersion) to correct for chromatic aberration. The design of multi-component lenses requires very exacting specifications for the glasses used. Professional optics books have

200 detailed tables of glasses with their glass numbers, densities, softening temperatures, etc [2,3] . We can calculate the glass index of refraction (n) by cutting the three left most digits from the glass number then, dividing them by 1000 and add 1 to the result.

n

=

float(int(~)) 1000 1000

+1

(1)

Where: N is the glass number. C

V=-

(2)

n

Where: c is Speed of light in vacuum = 2.998*108 mJs::::3 * 108 mJs, v is the speed of light inside a material, n is the refractive index of the material. From equations (1) and (2) we can calculate the speed of light inside the different types of glass. The delay time (t) in a glass type depends on the thickness and the speed of light inside a particular type of glass.

t

= -k

(3)

V

Where: k is the glass thickness, v is the speed of light in glass type. Table 2 illustrates glass types and their numbers, density, refraction index and speed of light inside them Figure 5 shows different delay time for different thicknesses. Table 2 Speed of light and refraction index for different glass types Glass

Glass ~umber(N

Density d=gmlcm3

n

Speed of light v =mls

!Borosilicate BK7

~17642

2.51

1.5l7

1.91

* lOe+S

~rownK5

522595

~.59

1.522

I.S99

* 10e+S

~ense barium crown

61S551

3.57

1.61S

1.7S7

* lOe+S

SK4 Dense flint SF6

S05254

5.1S

I.S05

1.602

* 10e+S

201

Time Delay

900

800

700 -

600

III

.!:

.

500

G.I

E

400 Imm

300

.5mm

.2mn

200

.! oS

100 -

I

0 Crown K5

Dense bnrium

Dense flint F6

crown SK4

glass Type

Figure 5 Delay time in different glass types for different thicknesses.

3. Compound Materials Glasses can be considered to be solutions, rather than chemical compounds. About 95% of all glasses are of the "soda-lime" type, containing silicon dioxide (silica), Na20 (soda), and CaO (lime). Crown glass is soda lime silica composite. Flint glasses contain 45-65% lead oxide they are high density, high-dispersion, high refractive index glasses. There are glasses which have barium oxide rather than lead oxide; they are called barium glasses. Barium glasses have refractive indices comparable to the flints, but have lower dispersions. Other heavy elements are used to make flint glasses, such as lanthanum and the rare earths. As alternatives to silica glasses, other "glass formers " such as boron oxide (B20s), phosphorus pent-oxide (P20S) and germanium oxide (Ge02) can be used [4]. There are many materials compounds, which have the same properties as silicon for example the five elements in figure 5. All five elements have 28 electrons in filled inner shells (K, L, and M shells) and electrons in the outer, less tightly

202 bound shell (N shell). The column III element GA has three outer electrons, and the column V element As has five outer electrons [4]. When these two elements are arranged in a lattice they share outer electrons to form covalent bonds with Ga atoms providing three electrons and As atoms, five electrons. There is, in effect, a Ga sub lattice and an As sub lattice (Figure 7). The compound gallium arsenide has the same response to light that silicon does; transparent to infrared light which is unable to break the electron bonds and opaque to visible light which can break bonds [4]. II

Thre02'

uutt!~

~'}(!': '!!'Qn_'

III

N·,hf.'H

1V

v

Five

VI

C)Uk'J'

.'Io'..;ih.:!1l

~Let.:trun'

Figure 6 Partial part of periodic Table for similar elements.

Figure 7 Two-dimensional representation of the Ga As lattice.

Alumina thin films are also of interest in microelectronics and optics industry as an insulating material due to their excellent electrical properties like large band gap and high dielectric constant. Alumina is known to exist in several transient meta stable structures. The most desirable form of crystalline alumina coating for applications is thermodynamically stable which is commonly known as corundum and has the hexagonal crystal structure. Alumina can withstand high temperatures of more than 1200 DC and has high hardness and excellent corrosion/oxidation resistant properties [5]. Zheng et ai, They use three materials; Nd20 3, Ah03 and MgF2' As 14 layers quarter wave stack with alternating high and middle index layers is constructed on the substrate. Then a six layers quarter wave stack with alternating low index and middle index layers is added to the previous stack. It is shown that the values of reflectance of p polarization and s polarization at ~ =1300nm are 59% and 50%, respectively, and the reflection-induced retardant is close to zero. An other three materials ZnS, Si0 2 and MgF2' were used. The results show that the values of reflectance of p polarization and s polarization at ~ = 1300 nm are 43% and 47%, respectively. The reflection-induced retardant is close to zero. [6]. Liua et al [7], They use Tetragonal deuterated potassium dihydrogen phosphate, K(DxHl_x)P04 (DKDP) crystal is a deuterated analog of Potassium dihydrogen

203 phosphate (KDP) crystal, and they are widely used in various electro-optical and non-linear laser devices. It is known that the electro-optical properties of the tetragonal DKDP crystals are much better than those of KDP. Besides, DKDP has been used as a frequency converter to avoid laser damage caused by stimulated Raman scattering, which may occur for KDP in a large aperture fusion laser .Consequently, considerable effort has been made in order to grow large and high optical quality DKDP crystals for use in these fields. In the past years, the KDP-type crystal growth techniques have developed greatly. Large aperture crystals can be grown by various methods, such as temperature reduction, solution circulation and the rapid growth method [7]. Zhong et al [8], study silicon wafer, they mentioned that it is important to form periodic microstructures on silicon surface for its application as optoelectronic devices. Many types of micrometer-scale surface structures have been fabricated on the surface of silicon irradiated by pulse laser. In particular, by irradiating silicon surface with femto-second laser in the presence of halogen-containing gases, Mazur's group created silicon surface covered with a semi-ordered pattern of sharp conical micro spikes. The material used in the experiments is commercial silicon wafer with a thickness of 2 mm. All experiments were carried out at room temperature in ambient atmosphere [8]. The silicon substrates diced from polished Si wafers and purchased from Microsens (Switzerland). Two samples (no. 1 and no. 2) were prepared as follows. An initial Si02 surface layer was grown up by oxidation of the substrates in an oven at 1000 oC during 12 h in synthetic air gas. The thickness of this layer was about 220 nm as determined by the time which was necessary to etch it completely using a buffered oxide etchant (BOE) solution: 7/l mixture of NH4F (40%) and HF (49%). The etching rate was 1.5nmls and an oxide thickness of 200 nm. Staircases of different thickness steps were then realized on the two samples by etching them sequentially for progressive periods of time with the previous BOE solution [9]. Photoluminescence spectra, photoluminescence decay curves and Raman scattering spectra have been investigated for stoichiometric rare-earth molybdate and tungstate compounds. NaNd(Mo04)2 and NaNd(W04)2 show emissions due to the transition 4F3/2/4I9/2 in Nd3C. A possibility of laser oscillation in NaNd(Mo04)2 is pointed from comparisons of the emission intensity and the decay time constant with Na Nd (W04)2 where laser oscillations have been reported. In NaLa(Mo04)2 and Na La (W04)2, observed emissions which are not related to La3C are probably due to the transitions in Mo04 2- and W04 2molecular ions, respectively, in scheelite crystal [10].

204

4.

Nonlinear Absorption (Multi Photon Absorption) and Upconversion:

Up-conversion lasers are among the most efficient sources of coherent visible and near-ultraviolet radiation. Laser emission has been demonstrated in both the continuous (cw) and pulsed modes, these types of lasers can provide practical solutions for applications as diverse as medical diagnosis and treatment, underwater surveillance and full color (RGB) all-solid state displays. Upconversion generally refers to energy transfer processes that are initiated by photon absorption. Up-conversion produces population in an excited state whose energy exceeds that of the pump photon. Optical emission from the excited state occurs at a wavelength shorter than that of the optical pump field, accounting for one of the more powerful features of this pump mechanism [11].

-----3 Emi ..io.

----.:-----.,_- 3

I- Emiuion

-r---'--.-

2

.

~I

A

B

Figure 9 Cooperative energy transfer upconversion between two three-level ions

Figure 8 Sequential two-photon absorption up-conversion in a three-level ion.

4.1. Sequential two-photon absorption Sequential two-photon absorption, also called sequential two-step absorption, is the most intuitive up-conversion process. It is also one of the best known types of up-conversion, having been discussed by Bloembergen as the basis for an infrared quantum counter. The upper state is populated by the sequential absorption of two photons. The first photon populates a long lived state intermediate in energy between the ground state and the upper fluorescing state .

.

~

~

2"

.~

2.

-

r---'"

....

:;..-

Figure 10 Sequential two-photon up-conversion in a modified three-level ion.

205 A second photon .promotes this ion from the intermediate state to the upper emitting level. Sequential two-photon absorption is illustrated in Figure 9. The ion energy levels are similar to the three-level system illustrated in Fig. 1 but with levels 2' and 3' included [11]. Photopolymers are attractive materials for optics, because of their high photosensitivity and refractive index modulation. A set of novel photopolymers based on a cellulose ester polymer binder doped with three differently functionalized acrylic monomers were prepared and investigated by differential scanning calorie-metric before and after laser irradiation at A.=514nrn. Evidence of refractive index modulation under irradiation was provided by spectroscopic. Holographic gratings were generated in these photopolymer samples by conventional optical interference method. Changes in diffraction efficiency were directly measured during irradiation of the films for mono, bi, and tri functionalized acrylic monomers doped into the polymer binder [4,12]. Polymethine dye (2 -[2- [3-[(l,3-dihydro -3,3-dimethyl -I-phenyl -2H-indol -2lidene)ethylidne]-2-phenyl-I-cyclohexene-1-yl]ethenyl]-3 ,3-dimethyl-1phenylin-dolium perchlorate) (PD3) that exhibits large excited-state absorption, using the rate equation approach, to achieve high contrast and fast switching. The transmission of a cw probe laser beam at 532 nm through PD3 dissolved in (i) ethanol and (ii) polyurethane acrylate (PUA), is switched by a pulsed pump laser beam at 532 and 650 nrn, respectively, which excite molecules from the ground state. The theoretical results show good agreement with the reported experimental results for case (i). The switching characteristics have been shown to be sensitive to variation in concentration, pump pulse width, peak pumping intensity, absorption, cross section of the excited state at 532 nm, and lifetime of excited state [13]. Organic molecules have emerged as excellent materials for molecular photonic applications, especially all-optical switching, due to their unique advantages and the ability to process them with conventional devices Polymethine dyes (PDs) in liquid solutions and polymeric media have been extensively studied as promising materials for laser and optoelectronic applications. Recently, PDs have been shown to exhibit strong transient reverse absorption, where the absorption cross section of the excited states is much larger than that of the ground state. For instance, for the PD3 dye (2-[2-[3-[(1,3-dihydro-3,3 - dimethyl-I- phenyl- 2 Hindol - 2 - ylidene ) ethylidne ] - 2 - phenyl-l-cyclohexene-I-yl]ethenyl]-3, 3dimethyl-I-phenylindolium perchlorate) dissolved in ethanol, the ratio of absorption cross-section of excited state to ground state has been shown to be as large as 200, at 532 nm. The photophysical properties of these dyes can be systematically modified by changing their molecular structure [14].

206 The photo chromic protein bacteriorhodopsin (bR) contained in the purple membrane fragments of Halobacterium halobium, has emerged as an excellent material for bio-molecular photonic applications due to its unique advantages. It exhibits high quantum efficiency of converting light into a state change, large absorption cross-section and nonlinearities, robustness to degeneration by environmental perturbations, high stability towards photo-degradation and temperature, response in the visible spectrum, low production cost, environmental friendliness, capability to form thin films in polymers and gels and flexibility to tune its kinetic and spectral properties by genetic engineering techniques, for device applications [15]. Organic materials have many features that make them desirable for use in optical devices, such as high nonlinearities, Flexibility of molecular design, and damage resistance to optical radiation, their use in devices has been hindered by processing difficulties for crystals and thin films. Focus is on a couple of these materials, which have undergone some investigation in the NASAlMSFC laboratories, and were also processed in space either by the MSFC group, or others. These materials belong to the classes of phthalocyanines and polydiacetylenes. These classes of organic compounds are promising for optical thin films and waveguides. Phthalocyanines are large ring structured porophyrins for which large and ultrafast nonlinearities have been observed. These compounds exhibit strong electronic transitions in the visible region and have high chemical and thermal stability up to 400°C [16]. Figure 11 A comparison of scanning electron micrographs of 1 ~m thick films of copper phthalocyanine deposited by physical vapor transport in the 3M PYTOS flight (STS-20) and ground control experiments. In micro gravity the films microstructure is very dense compared to that produced in unit gravity in the presence of convection. This difference in microstructure has a significant affect on the macroscopic film optical properties.

\ 19

A photodeposition process for film photodeposition onto quartz or glass surfaces enabled deposition of polydiacetylene (PDAMNA) films derived from 2-methyl4-nitroaniline, a well-known organic NLO material, by irradiation of monomer (the building block of a polymer) solutions with UV light. Polydiacetylenes are

207 highly conjugated polymers, i.e., the electrons in the polymer backbone are de localized and can move freely along the backbone capable of exhibiting very large optical nonlinearities with fast response times (less than 120fs: Its = 10-15 s). These response times are faster than they are for the fastest electronic switching by more than a hundred times. High quality films that have potential application in integrated optical circuits were produced. Films of PDAMNA that were processed in space on space shuttle flight STS-69 had superior optical quality (i.e. greater homogeneity, fewer defects) (Figure 12). This experiment also demonstrates that processing in micro gravity offers an opportunity to study certain parameters affecting the production of higher quality materials [16].

PD"\\'1N~\

Film ( 1 g)

I'J)A~J;o.IA

Film (lJ.g)

Figure 12 A comparison of a ground-grown po1ydiacetylene film with a micro gravity grown one.

Singh et al [17], Examine all-optical spatial light modulation in Platinum:ethynyl complex [bis((4-(phenylethynyl) phenyl) ethynyl) bis (tributylphosphine) platinum (II)], which exhibits strong RSA over a wide visible range. The structure of Pt:ethynyl molecule which also exhibits a large absorption crosssection of the ground state at its peak absorption wavelength (355 nm), fast transitions (ms), no overlap between the ground state and the triplet state absorption spectra at their respective peak wavelengths, and the flexibility to tailor its properties. Optical limiting response in Pt:ethynyl complex has been reported, which is both broad band across the visible and effective over pulse lengths ranging from picoseconds to hundreds of nanoseconds [17]. The above features make it a good prospective candidate for all-optical switching based on nonlinear excited-state absorption. The simplified energylevel diagram of Pt:ethynyl complex shows five levels. This five-level model is adequate to explain nonlinear absorption over a wide range of intensities. For Pt:ethynyl complex, the linear absorption spectra show a strong absorption peak at 355 nm with a tail that vanishes at 550nm while the triplet state absorption spectrum shows absorption peak at 600nm and negligible absorption at 355 nm. A 355 nm laser radiation that corresponds to third harmonic wavelength of Nd:YAG laser can be used to excite molecules from ground state So to a vibration state Sv of the first electronic excited state SI [15].

208

5. Conclusion From the demonstration above we can classify materials for optical design in major three categories, Organic, Organic metallic and metallic materials. Some studies depend on reflection and transparency of materials while the majority focuses on liner and nonlinear absorption of light. Different wavelengths are used to study materials effect and most of studies use visible range. The new trend is to use materials for infrared and ultraviolet, some studies try to invent materials for x-ray and other ranges of light spectral [20].

References 1. 2. 3. 4.

5.

6.

7.

8.

9. 10.

11.

Albert Tarantola, "Elements for Physics", Springer Berlin Heidelberg, New York, ISBN-13 978-3-540-25302-0, 2006. David E. Schmieder, "Course In Infrared and Electro-Optical Technology", Georgia Tech Research Institute, UK, 2007. Chetan Nayak, " Quantum Condensed Matter Physics - Lecture Notes", University of Cambridge, 2004. Herbert Walther, "Handbook of Atomic, Molecular, and Optical Physics", Springer Science & Business Media, New York, ISBN-I3: 978-0-38720802-2, 2006. Khanna Atul, Deep G. Bhat, "Nanocrystalline gamma alumina coating by inverted cylindrical magnetron sputter", Journal of Physics and Chemistry of Solids, 61, (2004), pp279-28I. Zheng Ping Wang, Jin Hui Shi, Shun Ling Ruan, "Designs of infrared nonpolarizing beam splitters", Optics & Laser Technology 39 (2006) pp.394399. Liua W.L.,_, Xiab H.R., Wangb X.Q., Lingb Z.c., Ranb D.G., Xuc J., Weic Y.L., Liua Y.K., Sunb S.Q., Han H., "Characterization of deuterated potassium dihydrogen phosphate single crystals grown by circulating method", Journal of Crystal Growth, 293, (2006) pp.387-393. Zhong Quan Zhao, Jian Rong Qiu, Chong Jun Zhao, Xiong Wei Jiang, Cong Shan Zhu, "Formation of array microstructure on silicon by multibeam interfered femtosecond laser pulses", Optics Communications,(2006). Singh c.P., Kapil Kulshrestha, Sukhdev Roy, "High-contrast all-optical switching with Ptethynyl complex", Optics, ww.sciencedirect.com. Kato A., Oishi S., Shishido T., T. Yamazaki T., Iida S., "Evaluation of stoichiometric rare-earth molybdate and tungstate compounds as laser materials", Journal of Physics and Chemistry of Solids, 66, (2005), pp.2079-2081. Richard Scheps, "Up-conversion Laser Processes", SSDI:007/727, frog. Quanr. Elecrr. 1996. Vol. 20. No.4 pp.271-358, Published by Elsevier Science Ltd, Printed in Great Britain.

209 12. Parag Sharma, Sukhdev Roy, C.P. Singh, "Dynamics of all-optical switching in polymethine dye molecules", Science Direct, Thin Solid Films 477, (2005), pp42- 47. l3. Sukhdev [{oy, Kapil Kulshrestha, "Theoretical analysis of all-optical spatial light modulation in organometallics based on triplet state absorption dynamics", Optics Communications 252 (2005), pp. 275-285. 14. Stefan A. Amarande, Michael J. Dmnzen, "Measurement of the thermal lens of grazing-incidence diode-pumped Nd: YV04 laser amplifier", Optics Communications 265 (2006) pp.306-3l3. 15. Singh c.P., Sukhdev Roy, "All-optical logic gates with bacteriorhodopsin", Science Direct, Current Applied Physics 3, (2003), pp163-169. 16. Abdeldayem Hossin, Donald O. Frazier, Mark S. Paley, and William K. Witherow, "Recent Advances in Photonic Devices for Optical Computing" , NASA Marshall Space Flight Center, Space Sciences Laboratory, Huntsville, al 35812. 17. Serge Gauvin, Joseph Zyss, "Growth of organic crystalline thin films, their optical characterization and application to non-linear optics", Journal of Crystal Growth no 166, (1996) pp.507-527 18. Yasuhiro Awatsuji, Yuu Shiuchi,Aya Komatsu, Toshihiro Kubota, "Design and fabrication of an Optimum holographic optical element lens for a femtosecond laser pulse using a hologram computer-aided design tool ", Optics and Lasers in Engineering no 44 (2006) P 975-990. 19. Nandigana Krishna Mohan, Quazi T. Islam, "Design of an off-axis HOE light concentrator to focus light from multiple directions in a plane", Science Direct, Optics and Lasers in Engineering, vo1.44, no.9, pp. 943-953, September 2006. 20. Xiaohua Ye, Peida Ye, Min Zhang, "All-optical NAND gate using integrated SOA-based Mach-Zehnder interferometer", Optical Fiber Technology, www.ScienceDirect.com.

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PROPOSED DESIGN FOR OPTICAL DIGITAL CIRCUITS

A YMAN ABDEL KHADER ISMAIL, PROF. IMANE AL Y SAROIT ISMAIL AND PROF. S.H.AHMED

Information Technology department, Faculty of Computers & Information, Cairo Universit,y 5 Tharwat Street. Orman. Giza, Egypt.

Designing digital circuits has a high priority in research field in the present time; it shall also still the main concern of many researchers in the future. Many studies in this field are in progress some are published and other still confidential. This paper proposes a design for elementary digital circuits; NOT, OR, AND; using light as direct inputs. These circuits then process these optical inputs to produce optical outputs without changing the light rays to any other type of energy or wave. The proposed design depends on mirrors, lenses and properties of light to introduce new digital circuits design using infrared rays as its inputs.

1. Introduction Light is an amazing phenomena, in dark ages it was the only way for far communication. First, fire signals were used to send messages. Then it was used for sending signals to identify coast for ships and military signals by using lenses, mirrors and big light lamps. Until discovery of electricity, light was the only way to transmit signals. Many studies were introduced in this field in 17 th and 18 th century to determine light speed, properties and components. Light is a complicated phenomenon: in some cases, it behaves like an electromagnetic wave, but in others, it behaves like a stream of special particles (photons). The energy of a photon is equal to nm where n Plank's constant divided by 2n and m is the cyclic frequency of the radiation [1,2]. Although light is recently used for optical transmission on networks by using fiber optics laser beams, infrared and ultra violet for fast transmission on networks [2] .But processing of the received optical data still depends on converting these optical inputs to electrical signals and converting electrical outputs (after processing) to optical for retransmission [10]. This makes a bottleneck for retransmission of data and video and audio signals, which leads to a delay and lost of information. In this paper, designs for elementary digital circuits; NOT, OR, AND; using light as direct inputs was introduced. These circuits process these optical

211

212

inputs to produce optical outputs without the need to change the light rays to any other type of energy or wave. The proposed design depends on mirrors, lenses and properties of light to introduce new digital circuits design using infrared rays as its inputs. This rest of this paper is organized as follow. In section 2, a recent study in this field is introduced. Section 3 illustrates the proposed optical digital circuits design together with their operation. Timing analysis of the circuits and synchronization condition is introduced in section 4. Finally, conclusion and future trends are discussed in section 5.

2. Recent Studies Many researches are in progress in the field of optical circuits, especially in digital circuit design. NASA has started a project for inventing high-speed optical digital circuits. Its researcher publish an AND circuit operates by using laser beams in [8], figure (1) shows this circuit. NEC, Pentagon and many other organizations are working confidentially on similar projects. Nanose-cond Ali-Optical MID-Logic GatlJ

,) I

A 1

a

c

1

1 0

0

l 0

1

I)

0

()

()

"'.,_J

.,::;-•."... . .... .........,.".~ •.".!'iN::l.::L_~.;:...... ; ~~...;.N;;.;'Y...;. .r.;,;·...,, _ ~~~~'j ~,<;_••

Figure 1 Structure of optical AND circuit NASA project [8J

3. Proposed Circuits Design In this section we will describe the internal design and operation of the proposed optical digital circuits NOT, OR and AND circuits.

3.1. NOT circuit

The proposed NOT circuit design depends on two facts: First, according to reflection law of light from a flat mirror, the reflected angle of a ray

213

is equal to the incident angle [1]. Second, a beam can be a destructive beam if its frequency is shifted by TC of the interfering beam (See appendix). [1,2] As shown in figure 2, we have two beams b l and b2 . b l enables the circuit, it always has the logical value 1 while b2 holds the input values. When b2 dropped on a high polished flat mirror mJ, ml reflects the beam b2 ' which have the opposite angle and shifted frequency of b2 . A lens L is used to gather the parallel beams b l and b2 ' at its focal where they interfere together (destructive interference). The resulted value is taken at a minimum point of the interference field. bI b2

...... bZ·

""';:::::::;

V

Figure 2 Structure of the proposed optical NOT circuit

3.1.1. NOT operation verification:

The NOT circuit has two inputs: • One enabled bJ, always equal to logic 1 in order to produce logical one as output when b2 equal to logical O. • One data input b z, which has two cases: 1- b 2= logical 0: In this case, no interfering will happened, so b l will pass through the lens L with a value of logic 1 at L focus. 2- b2= logical 1: • According to distance from input port to the mirror, the phase of b 2 will be shifted by TC. • When b2 fills on the mirror, it will reflect b2 as b z' towards the lens. • The lens L gathers b l and b2 ' at its focus, where they interfere together in a destructive interference [1], in this case the distance between interference fringes can be recognized. So we can find more than one minimum point of the interference field (dark parts) at which we can get value of logic O.

214 Table 1 NOT circuit behavior b

b

2

I

0

I

1

I

b2'

0 Value = I, phase shifted by 1t

Interference between b" b2 ' Null

Outpu t 1

Destructive interference [2]

0

3.2. OR circuit The proposed OR circuit uses reflection and refraction laws [2]. The circuit is shown in figure 3, it consists of three mirrors mb m2 and m3' ml and m2 are 90% polished flat mirror while m3 is a 70% polished concave mirror. ml reflects beam b l near the center of m3 as b l ', m2 reflects b2 near the center of m3 as b2'. The mirror m3 reflects b l 'and b 2' as b3. bi I

b3

Figure 3 Structure of the proposed optical OR circuit

The following scenario is followed in case of logical I input beam: • Approximately 10% (transparency of the mirror = 10%, so 10% of the incident ray will pass through the mirror) of the beam is refracted through its corresponding mirror and lost is lost. • The corresponding mirror about 90% (polishing ratio of the mirror surface equal to 90%, so 90% of the incident ray will be reflected from the mirror surface) of the incident beam towards the concave mirror m3 as a new beam, and near to center of m3' • The mirror m3 refracts about 30% (transparency of the mirror = 30%,) and reflects 70% ((polishing ratio of the mirror surface equal to 70%) of the new beam, so the final beam b3 obtain about 63% (illumination of bI', b2' about 90%of bi and b2,so total illumination of b3 = .9 *.7 = 63% ) of the original beam. Therefore, we can recognize illumination at the output port, which gives value of logic 1.

215 3.2.1. OR operation verification:

The OR circuit has two inputs b I and b z, so its truth table has four cases: 1- bI=b z= logical 0: Of course, no illumination at the output exists and b3 =

o.

2-

bI=logical 0 and b z= logical 1: • The beam bz fills on the appropriate flat mirror mz. • Approximately 10% of bz is refracted through the mirror mz and lost. • The flat mirror mz reflects about 90% of the incident beam bz towards the concave mirror m3 as bz', and near to center of m3. • The mirror m3 refracts about 30% and reflects 70%of the incident beam bz', so the final beam b3 obtain about 63% of original beam bz. Therefore, we can recognize illumination at the output port, which gives value of logic 1. 3- bI=logical 1 and b z= logical 0: • The beam b I fills on the appropriate flat mirror mI. • Approximately 10% of b I is refracted through the mirror mI and lost. • The flat mirror mI reflects about 90% of the incident beam b I towards the concave mirror m3 as b I', and near to center of m3. • The mirror m3 refracts about 30% and reflects 70%of the incident beam b I', so the final beam b3 obtain about 63% of original beam b l . Therefore, we can recognize illumination at the output port, which gives value of logic 1. 4- bI=logical 1 and bz= logical 1: • The beams b2 and bl acts exactly as mentioned in 2 and 3 respectively. • Therefore, the mirror m3 refracts about 30% and reflects 70% of both incident beams b I' and bz'. So the final beam b3 have about 126% (illumination of bl' = illumination of b2' = 90%, illumination of b3 = 70% ofbl '+b2' =70%* (2*90%)) of original beam b I or b z where we can recognize illumination at the output port, which gives value of logic 1.

216 Table 2 OR circuit behavior b

b

2

I

0

0

b I' after reflection frOIIl IIII 0 ilIumination=90% ofb l shifted Dhase bv 11:

0

I

I

0

0

J

I

ilIumination=90% ofb l shifted Dhase bv 11:

3.3.

b/ after reflection froIIl III2 0

Output (b3) 0 illumination = 0.9*0.7 =63% of b l same phase as b I, value = I

0 illumination=90%of b2 shifted Dhase bv 11: illumination=90%of b2 shifted Dhase bv 11:

illumination = 0.9*0.7 =63% of b2 same phase as b2, value =1 iIIumination=(0.9*0. 7)*2= 126% of b l or b2 same phase as b l and b2, value =1

AND circuit

The proposed AND circuit uses reflection and interference laws [2]. The shown circuit in figure 4 has 2 inputs beam b l and b2. Those inputs are shifted then reflected by two high polished mirrors ml and m2, as b l ' and b2' respectively. Three Lens are used, Lb L2 and L 3. LI gathers b l and b 2' as b3. L2 gathers b 2 and b l ' as b4 . L3 gathers b3 and b4 as the output of the circuit. The resulted value is taken near a minimum point of the interference field figure (4).

1..3

Figure 4 Structure of the proposed optical AND circuit

The following scenario is followed in case of logical 1 input beam: • Its phase will be shifted by 1[ (to produce destructive interference) and then reflected from its corresponding flat mirror mj towards its corresponding lens as a new beam'. • The original beam moves directly to its corresponding lens and passes through its focus. • The new beam passes through the focus of the other lens.

217

• L3 gather the two beams at its focus, where they interfere together (destructive interference to ensure that the illumination of the output does not exceed the value of logical 1). AND operation verification: The AND circuit has two inputs b l and b2, so its truth table has four cases: 1- bl=b2= logical 0: Of course, no illumination at the output exists at the output port and the resulting value =0. 2- bl=logical 0 and b2= logical 1: • The phase of b2 will be shifted by n; and then reflected from the flat mirror ml towards the lens LI as b2'. • The original beam b2 moves directly to the lens L2 and passes through its focus as b3. • b2' passes through the focus ofL I as b4 • • L3 gather the two beams b3 and b4 at its focus, where they interfere together (destructive interference). Therefore, an illumination isn't recognized so the resulting value is logical o. 3- bl=logical 1 and bz= logical 0: • The phase of b l will be shifted by n; and then reflected from the flat mirror mz towards the lens L z as b l ' . • The original beam b l moves directly to the lens LI and passes through its focus as b3. • b l ' passes through the focus of L2 as b4. • L3 gather the two beams b3 and b4 at its focus, where they interfere together (destructive interference). Therefore, an illumination isn't recognized so the resulting value is logical O. 4- bl=logical 1 and b2= logical 1: • As explained before, b l and b2' (which has a value of b2 and its phase is shifted by n;) interfere together, at the focus of L I. Also, b 2 and b l ' (which has a value of b l and its phase is shifted by n;), interfere together, at the focus ofL2, • The two beams b3 and b 4 are collected near a minimum point of the interference field with a value about 50% of the original beam and has the same phase. • L3 gather b3 and b4 at its focus where they interfere together with a constructive interference (they have the same phase) giving the output a value about 100% (final illumination equal approximately to the sum of the incident rays in constructive interference, where b3 = b4 = 50% of the original beams) of the original beams, resulting a value of logical 1.

218

Table 3 AND circuit behavior bb 2

bl '

I

00

0 value=1 01 shifted phase bv 1[ I 0

0

value=1 1 I shifted phase by 1[

b z'

b3

b4

Output 0 value =0 Destructive Interference value =0 Destructive Interference

0

0

0

0

value=1 same phase as b l

value=1 shifted phase by 1[

value=1 value=1 value=1 shifted shifted phase by 1[ same phase as b2 phase bv 1[ Destructive Interference Destructive Interference value=1 illumination = illumination = =50% shifted =50% same phase as b l or ~ phase by 1[ same phase as b l or bz

value=1 Constructive Interference illumination = =100% same phase as bland b2

4. Timing Analysis of the Circuits Circuits timing depends on the longest path that beam travel through, so that if we want to reduce this time we must reduce these paths as possible. The longest path of the NOT circuit is b2b2 '. For the OR circuit, the longest paths are either blb l 'b3 or b2b2 'b3 • For the AND circuit, the longest path is either b lb l 'b4 or b2b2 'b 3 . To make these circuits works at IllS these paths must be less than (3*1Q8)/ 1Q9=30cm (See Appendix A). On the other hand, external interference may affect the operation of the circuits and cause undesired results, to prevent external interference (which will lead to wrong results), we must shield these circuits with external cover.

5. Conclusion and Future Trends In this paper, a new design for elementary optical digital circuits (NOT, OR, AND) using infrared rays was proposed. Functions of these circuits were proved theoretically. As future trend, we shall test these circuits practically. In addition, we shall study the effect of combination of these circuits when used in large-scale circuits, since they may need to be enhanced.

219

Appendix A. Constant and Properties The following constants and properties are used in the paper:

A.I. Constants: Light speed = 2.997 * 10 8 m1s [1,2]. Infrared wavelength >=.76 Jlm [1,2]. Visible light wavelength rang (0.40 - 0.76) Jlm [1,2]. Frequencies of Visible light = (0.39-0.75)* 10 15 Hz [1,2] A.2. Properties: Reflection laws: IThe reflected ray lies in the same plane with the incident ray.2 The angle of reflection is equal to the angle of incident [2,3,4]. Destructive interference: Two interfered waves have a destructive interference if the phase of one of them is shifted by n with the respect to the other (advancing or delaying shift) [2,4,5,6,7] Constructive interference: Two interfering waves have a constructive interference if they have the same phase or the phase of one of them is shifted by 2n with the respect to the other (advancing or delaying shift) [2,9]. Phase Shifting: We cannot shift real time signals advancing shifting. Most of elementary circuits cannot predict future inputs. Taking this in consideration, we use delay shift. Delay shifting can be done by two ways, first decreasing the speed of signal, or, second increase the distance that the signal must travel. To make a beam a destructive beam, its phase must be shifted by n. This can be done by increasing the path that beam must travel by (m+1I2)A, where m = (0,1,2, .. .... ... ) and A is the wavelength of the beam[ 1,2,3,4,5,6,7]. Interference field: It is the region in which two or more waves overlap. Within this region, there are alternating places with maximum and minimum intensity of light, which is called fringes [2]. At a minimum point there is a dark place, and light intensity increases by moving to the left or to the right side till maximum point we find high intensity of the interference field.

References 1. 2. 3.

A.V. Oppenhim, A.S. Willsky and W.S.H. Nawab, "Signals and Systems", Prentice Hall, 1997. I.V. Savelyev, "Physics, A General Course", Vol.2 Part II and III, Mir Publishers Moscow, 1989. W. Smith, "Modern Optical Engineering", SPIE Press McGraw Hill, New York, 2000.

220

4.

T. Rossing and C. Chiaverina, "Light Secince: Physics and the visual Arts", Prentice Hall, 1999. 5. J. Palmer, "Handbook of Optics", vol. 2, 2nd Edition, McGraw Hill, 1995. 6. George E. Anner, " Elementary electronic circuits", Prentice Hall, N. J. 1997. 7. E. J. Angelo, "Electronic circuits", Second Edition, McGraw Hill, 1964. 8. NASA, "Optical Projects", http://www.nasa.com 9. S. Diez, C. Schmidt, R. Ludwig, H.G. Weber, P. Doussiere, and T. Ducellier, "Effect of Birefringence in a Bulk Semiconductor Optical Amplifier on Four-Wave Mixing", IEEE Photonic. Technical Letters, October 1998, pp. 212-214. 10. F.Young Song, Wea Ming and Wing Dar, "Optimal Ranging Algorithm for Medium Access Control in Hybrad Fiber Coax Networks", IEEE transactions on communication, October 2002, pp. 2319-2326.

III - Laser Applications in Medicine 111-1. Contributed Papers

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PHOTO-INDUCED EFFECT ON BACTERIAL CELLS* M. H. EL BATANOUNy12, REHAB M. AMIN2, M. I. NAGAi & M. K. IBRAHIM' [email protected]

1. Faculty 0/ Medicine, Cairo University, Egypt. 2. NILES, Cairo University, Egypt. 3. Faculty o/Science, Ain Shams University, Egypt.

Bacterial resistance against antibiotics is an increasing problem in medicine. This stimulates study of other bactericidal regimens, one of which is photodynamic therapy (PDT), which involves the killing of bacterial species by low power laser light (LLL) in the presence of photosensitizing agent. It has already been shown that, various gram- negative and gram-positive bacteria can be killed by photodynamic therapy in vitro, using exogenous sensitizers. The mechanisms of laser action on bacteria are not adequately understood. Here, PDT on H. pylori, as an example of gram negative bacteria was studied. The ultra structure changes of the organism after PDT were examined under electron microscope. Neither Irradiation with laser without sensitizer nor sensitizing without laser has any lethal effect on bacterial cells. However, the successful lethal photosensitization was achieved by applying certain laser dose with the corresponding concentration of the photosensitizer. On the other hand, PDT has no significant effect on the genomic DNA of the cells. Key words: Photodynamic therapy (PDT), H. pylori, Low power Laser Light (LLL).

'This work is supported by NILES, Cairo University.

223

224 1. Introduction

Bacterial resistance against antibiotics is an increasing problem in medicine where, the prolonged use of antibiotics makes alteration of the natural microflora (6, 9). This stimulates study of other bactericidal regimens, one of which is photodynamic therapy (4). It has already been shown that, various gram-negative and gram-positive bacteria can be killed by photodynamic therapy in vitro, using exogenous sensitizers. Photodynamic therapy (PDT) involves the killing of bacteria by low power laser light in the presence of photosensitizing agent. Excitation of the sensitizer by absorption of light of appropriate wavelength converts the sensitizer to its photoactive triplet state. This state reacts with either a local substrate (type 1 reaction) to form cytotoxic radicals, or with molecular oxygen (type 2 reaction) to produce cytotoxic singlet oxygen (11, 15). During the past decade, Helicobacter pylori has become recognized as one of the most common human pathogens, colonizing the gastric mucosa of almost all persons exposed to poor hygienic conditions from the childhood. H.pylori causes chronic active gastritis and is a major factor in the pathogenesis of duodenal ulcers, and to a lesser extent, gastric ulcers. In addition, the presence of this bacterium is now recognized as a risk factor for gastric adenocarcinoma and lymphoma (4, 12). It was reported that, H.pylori could be killed by lethal photosensitisation effect with aluminum sulphonated phthalocyanine (a mixture of di-, tri- and tetra sulphonated derivatives) after incubation for 4 hours, and then expos to 300 seconds of laser light supplied by a copper vapour pumped dye laser tuned to 675 nm (1). Lethal photosensitisation of H.pylori attached to a gastric carcinoma cell line may be done with haematoporphyrin derivatives (HPD) (100 Ilg!ml) and energy doses of between 1 and 10 J/cm2 supplied by a 200 W xenon arc lamp (with a 515 nm long pass fitler) (20). The susceptibility of H.pylori to lethal photosensitisation with various photosensitisers was determined. Crystal violet and thionin were ineffective as sensitisers, but zones of inhibitions appeared with methylene blue (MB), protoporphyrin IX (PPIX), haematoporphyrin derivatives (HPD) , toluidine blue a (TBO) and disulphonated aluminum phthalocyanine (S2). S2 (100 Ilg!ml) with a laser energy density of 16 J/cm2 , HPD (100 Ilg!ml) with 160 J/cm2 , MB (100 Ilg!ml) with 21 J/cm2 , PPIX (150 Ilg!ml) with 320 J/cm2 and TBO (50 Ilg!ml) with 160 J/cm2 all reduces bacterial viability by > 99 % (13).

2. Aim of the work It is aimed to study the photodynamic effect on H. pylori, as an example of gram negative bacteria. Also, it is aimed to evaluate the efficiency of this modality when using

225 two different photo sensitizers with their corresponding lasers and to investigate the effect of different parameters such as sensitizer concentration and light dose on bacterial killing.

3. Material & Methods 3.1. Collection of biopsy samples Biopsies were taken from fifty patients. There were 35 male and 15 female. Age ranged from 30-70 years. Out of 50 patients, 10 were gastric ulcer patients, 17 were duodenal ulcer patients, 13 were gastritis patients and 10 were retlux oesophagi tis patients. Standard biopsy forceps was introduced into the operating channel of the endoscope where two biopsies were taken (from the body & the antrum) in 0.5ml saline.

3.2. Isolation and Identification of the organism

Biopsy specimens were homogenized in saline using a mechanical tetlon homogenizer for one minute. Two drops of homogenate were placed on the surface of plates of a selective medium. These drops were spreaded over the whole surface of the plates containing selective medium. Plates were then incubated in a microaerobic atmosphere at 37°C for 2-5 days (8). A suspension of H.pylori was prepared in WilkinsChalgren (WC) anaerobe broth neutral pH and vortex mixed to achieve a uniform suspension. H.pylori isolates were identified by Gram stain and Biochemical tests (Urease, Catalase and Oxidase) (3).

3.3. Photodynamic effect Photosensitizers

Two photosensitizers were tested. Toluidine blue 0 (TBO) and methylene blue (MB). Each sensitiser was prepared in Wilkins-Chalgren (WC) anaerobe broth medium and filter-sterilized before use. TBO was applied with concentration 50,100, 150,200 & 250 Jlglml while MB applied usig concentration 50, 75, 100,200 &300 Jlglml.

226 Light sources Two types of lasers were used. For TBO, a 5.5 mw helium neon (He-Ne) gas laser with a wavelength of 632.8 nm in a beam with a diameter of 1 mm was used. It was applied with energy densities 42, 84, 126, 168, 210, 420, 630 & 840 J/cm2 . While for MB , a gallium-aluminum arsenide (GaAlAs) laser with a wavelength of 650 nm and power range 20-100 mw was used for a period of 5 minute. It was applied with energy densities 13, 19,25,31 , 38, 44,50,56,63 J/cm2 •

3.4. Assessment the effect of laser light on bacterial viability

3.4.1 Inhibition zone 2 ml of bacterial suspension were added to 2 ml of sensitizer solution and mixed thoroughly. After incubation for 5 minutes, Iml was spread over the surface of the selective medium plate, which was then allowed to dry at 37°C before irradiation with laser. Plate consisting of the bacterial suspension plus WC broth in place of the dye solution was treated with the same fashion to determined the effect of laser light alone on bacterial viability. Plate consisting of the bacterial suspension plus dye solution was prepared but was not exposed to laser. Hence, the effect on bacterial viability of the photosensitizer alone could be determined. Plate consisting of the bacterial suspension plus WC broth alone was left unirradiated. Plates then were incubated at 37°C for 3-5days in a microaerophilic atmosphere and then examined for zones of inhibition of bacterial growth (13).

3.4.2 Colony forming units (CFU) One hundred III of bacterial suspension were pipetted into one well of a 96-well tissue-culture followed by 100 III of sensitizer in WC broth and a 4-mm sterile mixing bar.Then, the contents of the well were exposed to laser light while, mixing with the magnetic stirrer continued. At the end of the exposure period, 10 III were pipetted from the well into 90 III of sterile broth. And serial dilutions were then prepared, and plated onto Columbia blood agar base with Dent's supplement to determine the number of surviving organisms. Bacteria treated with both sensitizer and laser (Laser & Sensitizer group). Another well was filled in the same way but it was not exposed to laser light (Sensitizer group). Additional well was processed in an identical manner except that WC broth was added in place of sensitizer and the well was exposed to laser light (Laser

227 group). Control well consisted of unirradiated sensitizer-free bacterial suspension (Control group).Colony counts were performed after incubation of plates in a microaerophilic atmosphere for 5days at 37°C (13).

3.5. Statistical analysis

A student t test was performed on the data comparing the mean count of each test well laser and sensitizer group to that of the wells, which include laser group, sensitizer group & control group. The two wells laser group and sensitizer groups were also compared with control group.

3.6. Assessment the Ultrastructure changes of the organism after PDT using Electron microscope

Two samples (control and test) were subjected to electron microscopic examination. Control sample, it was bacterial suspension which was not, exposed to laser or sensitizer while test sample was exposed to He-Ne laser after sensitization with TBO. The pellet obtained from the centrifugation of the bacterial suspension was processed according to Holstein (7).

4. Results 4.1. Isolation and Identification of Helicobacter pylori Helicobacter pylori were positive in 9 gastric ulcer patients (90%), 15 duodenal ulcer patients (88%) and 6 gastritis patients (46%) while all reflux oesophagi tis patients were H.pylori negative. The mean age of infected patients was 60 years old. 4.2. Assessment the effect of laser light on bacterial viability Irradiation of the bacteria with He-Ne laser 632.8nm or GaAIAs diode laser 650nm for up to one hour in the absence of sensitizer had no detectable effect on the viability of the organism. Similarly, at the all concentrations used, TBO or MB had no detectable effect on bacterial viability in the absence of laser light. Results of inhibition zone with TBO and MB are given in tables (1&2). TBO (100 fig/ml) with a laser energy density of 210 J/cm2 , and MB (100 fig/ml) with 25 J/cm2 both reduced bacterial viability by > 90 %.

228

4.3. Statistical analysis Data of statistical analysis are shown in tables (3& 4). Viable cell count of H.pylori using photosensitizer was significantly decreased by laser irradiation while, the laser light alone, sensitizer alone or absence of both of them had almost non significant effect. 4.4. Assessment the Ultrastructure changes Electron micrograph of normal H.pylori shows the organism with a full coccoid form with a double membrane system (cell wall and cytoplasmic membrane) and high electron density in the cytoplasm. On the other hand the Electron micrograph of H.pylori after PDT shows rupture of the double membranes (cell wall and cytoplasmic membrane) of the bacterial cells with discharging of the intracellular contents.

5. Discussion H. Pylori was found to be associated with gastritis, duodenal and gastric ulcers and more recently, with carcinoma of the stomach. Nearly, 100 % of patients with duodenal ulcers are colonized with H.Pylori. Over 80 % of patients with duodenal ulcers and which was associated with H.Pylori relapse within 12 months after healing of their ulcers. Eradication of the organism reduces that relapse rate to fewer than 5% (16). This study has shown that, H.Pylori was isolated from 9 out of 10 gastric ulcer patients (90%), 15 out of 17 duodenal ulcer patients (88%) and 6 out of l3 gastritis patients (46 %) while reflux oesophagitis patients were H.Pylori negative. Irradiation of H.Pylori with light from either the He-Ne or GaAlAs diode laser, in the absence of sensitizer had no effect on bacterial viability. Also, both Toluidine blue 0 (TBO) and methylene blue (MB) had no significant effect on bacterial viability in the absence of laser light (Table 3&4). These results were similar to those obtained in the previous study (l3). No lethal effect was detected when using TBO at concentration 50 Ilg!ml for all energy densities used. The least concentration at which lethal effect on bacterial cells was detected using TBO at concentration 100 Ilg!ml with energy densities from 126 J/cm2 and up. Irradiation of H.pylori with He-Ne laser at energy density 210 J/cm2 after sensitization by TBO at concentration 100 Ilg!ml had a successful lethal photosensitization effect on bacterial cells where 93 % of bacteria were killed. The optimum concentration of TBO that was chosen for lethal photosensitization in this study was 100 Ilg!ml (Table 1) which, was higher than (50 Ilg!ml) the concentration used by Millson et al (13). This difference may be due to the power of applied laser where, the power used in the present study was 5.5 mw while that used in the other study was 7.3 mw.

229 It was reported that, successful killing of gram positive streptococcus sangious with TBO (2 .5 Jlg/ml) and He-Ne laser (42 J/cm2) (17) . This low concentration wasn't surprising because of the outer membrane structure of H.Pylori, which was gram negative. This membrane structure gave bacteria some resistance to dye. So that high concentration of dye was required to achieve lethal photosensitization effect. The efficacy of lethal photosensitization of bacteria was thought to depend upon the presence or absence of the outer membrane that surrounds the peptidoglycan membrane of bacteria. So that, gram-positive bacteria (i .e. those without this outer membrane) were susceptible to lethal photosensitization better than, gram negative bacteria (i.e. those with this outer membrane) (10). In this study, the energy dose of He-Ne laser required to kill 93 % of bacteria was 210 J/cm2 with exposure time 5 min while that used by Millson et al to kill 99% of bacteria was 160 J/cm2 with exposure time 5min (13). This difference in energy density may be due to the power of applied laser where, the power used in the present study was 5.5 mw while that used in the other study was 7.3 mw. Successful killing of the gram negative periodontopathogens Fusobacterium nucleatum, Porphyromonas gingivales and Actinobacillus actinomycetemcomitans was achieved by irradiation with an energy dose of only 16 J/cm2 from He-Ne laser after sensitization with TBO (50 Jlg/ml) (19). This energy dose was considerably lower than that required for killing H.Pylori. It was shown from this data that, the requirement of a high-energy dose did not depend only on the gram status of the organism but also on the mechanism of cell death (type I & type II reaction) which may play an important role. In the present study, it was found that, no lethal effect was detected when using MB at concentrations 50 Jlg/ml and 75Jlg/ml for all energies used. The least concentration at which lethal effect on bacterial cells was detected using MB at concentration 100 Jlg/ml with energy densities from 25 J/cm2 and up. Irradiation of H.pylori with energy density 25 J/cm2 from GaAIAs diode laser after sensitization by MB at concentration 100 Jlg/ml had a successful lethal photosensitization effect on bacterial cells where 98 % of bacteria were killed. This result was in harmony with Millson et al who reported that, at the same concentration, 99% of H.Pylori was killed with energy density 21 J/cm2 (13). Electron micrograph of normal H.pylori shows the organism with a full coccoid form with a double membrane system (cell wall and cytoplasmic membrane) and high electron density in the cytoplasm. This finding was in agreement with Benaissa who reported that, in vitro H.pylori converts from a bacillary form to a full coccoid form where, the organism appeared with a full coccoid form keep a double membrane system, a polar membrane and invaginated structures (2). On the other hand the Electron micrograph of H.pylori after PDT shows rupture of the double membranes (cell wall and cytoplasmic membrane) of the bacterial cells with discharging of the intracellular contents. This finding showed that, the main target of photodynamic effect using Toluidine blue 0 as a photosensitizer in the phenothiazinium group was the cell wall and the cytoplasmic

230

membrane. This finding showed that, the main target of photodynamic effect using Toluidine blue 0 as a photosensitizer in the phenothiazinium group was the cell wall and the cytoplasmic membrane. It was found that, although TBO bind tightly to DNA, hence its use as histological stains (13); TBO did not enter the bacterial cells as easy as human cells due to the presence of a cell wall and extra-cellular structure such as capsule and slime layers (17). TBO did not have mutagenic potential as its site of action was primarily the cytoplasmic membrane rather than the nucleus (18). Moreover, PDT had generally a low potential of causing DNA damage (14). In conclusion, Laser light or sensitizer alone did not affect bacterial viability. Lowpower laser light can kill sensitized H.pylori when irradiated for a short period of time and this may offer a new approach to the treatment of H.pylori infections. Also, the ultrastructure changes of H.pylori after photodynamic treatment showed that, the sites of attack which, cause bacterial death, were cell wall and cytoplasmic membrane. However, more extensive experiments using photo sensitizers and law power laser should be conducted both in vitro and in vivo studies to develop a photochemotherapeutic system that could be clinically tested for its effectiveness to eradicate H.Pylori. Also, the biggest challenge is likely to be the development of a light delivery system to ensure that a minimum effective light dose reaches all colonized regions. However, if this technical difficulty can be overcome, endoscopic therapy for H.Pylori could offer a credible alternative to current endoscopic regimen.

Table l. Screening for lethal photosensitization of H.py/ori with TBO on the surface of agar plates after exposure to He-Ne laser Inhibition of growth at energy density (J/Cm' ) (time of exposure / min) 84 126 168 210 420 630 (2) (3) (4) (5) (10) (15)

Conc.ofTBO (~glml)

42 (I)

-

-

50 100 150 200 250

-

+ + + +

-

-

+ + + +

+ + + +

840 (20)

-

-

-

+ + + +

+ + + +

+ + + +

Table 2. Screening for lethal photosensitization of H.py/ori with MB on the surface of agar plates after exposure to GaAIAs laser for 5 minute Conc.OfMB (~glml)

50 75 100 200 300

Inhibition of growth at energy density (J/Cm' ) (time of exposure = 5 min) 13 19 25 31 38 44 50 56 63

-

-

+ + +

+ + +

-

-

-

-

-

+ + +

+ + +

+ + +

+ + +

+ + +

-

-

-

231

Table 3. Comparison between mean number of colonies of H. pylori in control group, laser group (He-Ne 632.8nm), sensitizer group (TBO) and test group (L+S) Group Control He-Ne laser TBO He-Ne laser + TBO

Mean 33.9 ±12.8 33.5 ±12.9 33 ±11.8 2.2 ±1.3

P Value

Significance

% of reduction

0.5 0.4 8.2 E-15

N.Sig. N.Sig. H.Sig.

94%

Table 4. Comparison between mean number of colonies of H. pylori in control group, laser group (GaAIAs diode laser 650 nm), sensitizer group (MB) and test group (L+S) Group Control Diode laser MB Diode + MB

Mean 37.3 ± 18.6 37.9± 17.3 37.6 ± 18 0.7 ± 1

P Value

Significance

% of reduction

0.2 0.3 4.16E-12

N.Sia . N.Sig. H.Sig.

98 %

Electron micrograph showing the ultra structure of normal H.pylori. Right, ( He-Ne laser with TBO) Left, ( No laser & No TBO)

232 Acknowledgments I would like to give special thanks to all members of National Institute of Laser Enhanced Science for their kind help and fruitful cooperation.

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J. Bedwell, J. Holton, D. Vaira, J. MacRobert and G. Bown. (1990).Lancet; 335: 289-292.

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M. Benaissa, P. Babin, N. Quellard, L. Pezennec, Y. Cenatiempo, and J. Fauchere. J. Infect. Immun. 64 (6), 2331(1996).

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M. Cheesbrough. Great Britian at the university press, Cambridge. 58 (1994).

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J. Dobson, M. Wilson, and W. Harvey. J. Arch Oral Bio. 37,883 (1992).

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Dubois. EID 1(3), 1(1995).

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S. L. Gorbach. Gastroenterol. 99, 863(1990).

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F. Holstein, E. Roosen-Runge and C. Schirren. Groose-Verlag, Berlin, 14 (1988).

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Lee and F. Megraud. W.B. Saunders Company LTd. London .17 (1996).

9.

R. P. H. Logan, P. A. Gummett, J. J. Misiewiez, Q. M. Karim, M. M. Walker and J. H. Baron. Lancet 338, 1249 (1991).

10. Z. Malik, J. Hanania and N. Yehayau. J. Photochem. Photobiol. 5,281 (1990). 11. M. J. Manyak (1990). J. Cancer; 3: 104-109. 12. P. Michel, W. D. Adrian, E. V. Angeline, A. V. Richard, A. Dietrich, M. A. Tom and J. A. Peter. J. Photochem. Photobiol. B 40, 132 (1997). 13. E. M. Millson, Wilson, A. J. Macrobert, J. Bedwell and S. G. Bown . .J. Med. Microbial. 44, 245 (1996).

14. J.Moan, K. Berg and E. Kvam. Ed, Kessel, D., CRC press, Boston, 197(1992).

233 15. H. Pass (1993). J. Natl Cancer Inst; 85: 443-456. 16. E. A. Rauws and G. N. Tytgat. J. Lancet 335,1233 (1990) . 17. N. S. Soukos, M. Wilson, T. Burns and P. M. Speight. J. Lasers Surg. Med.18, 253 (1996). 18. E. M. Tuite and J. M. Kelly. J. Photochem. Photobiol. 21,103 (1993). 19. M. Wilson, J. Dobson and S. Sarkar. Oral Micobiol. Immunol. 8, 182 (1993). 20. H. Wolfson, K.Wang, D. Alquist, M. Pittelkow and F. Cockerill (1992). Elsevier Science publishers B.V. Amsterdam. 281-285 .

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LASER AND NON-COHERENT LIGHT EFFECT ON PERIPHERAL BLOOD NORMAL AND ACUTE LYMPHOBLASTIC LEUKEMIC CELLS BY USING DIFFERENT TYPES OF PHOTOSENSITIZERS MOHAMED H. EL BATANOUNY General and Vascular Surgery Department, Faculty of Medicine, Cairo University AMIRA M. KHORSHID, SONY A F. ARSANYOS, HESHAM M. SHAHEEN and NAHED ABDEL WAHAB Clinical Pathology Department, National Cancer Institute, Cairo University SHERIF N. AM IN Clinical Pathology Department, Faculty of Medicine, Cairo University. MAHMOUD N. EL ROUBY Immunology & Virology Unit, Cancer Biology Department, National Cancer Institute, Cairo University MONA I. MORSY National Institute of Laser Enhanced Sciences

Photodynamic therapy (PDT) is a novel treatment modality of cancer and noncancerous conditions that are generally characterized by an overgrowth of unwanted or abnormal cells. Irradiation of photosensitizer loaded cells or tissues leads via the photochemical reactions of excited photosensitizer molecules to the production of singlet oxygen and free radicals , which initiate cell death. Many types of compounds have been tested as photosensitizers, such as methylene blue (MB) and photopherin seemed to be very promising. This study involved 26 cases of acute lymphoblastic leukemia and 15 normal volunteers as a control group. The cell viability was measured by Light microscope and tlowcytometer. Mode of cell death was detected by tlowcytometer and electron microscope in selected cases. The viability percentage of normal peripheral blood mononuclear cells (PBMC) incubated with methylene blue (MB) alone or combined with photo irradiation with diode laser (as measured by light microscope) was significantly lower than that of untreated cases either measured after I hour (p
235

236 He:Ne laser compared to normal untreated cells. The decrease in the cell viability percentage was significantly lower with the use of PDT (photopherin and He:Ne laser) compared to either photopherin alone or He:Ne laser alone. The decrease in viability was more enhanced with increasing the incubation time. The same effects reported on normal cells were detected on leukemic cells on comparing different methods used. However a more pronounced decrease in cell viability was detected. The most efficient ways of decreasing viability of leukemic cells with much less effect on normal cells was the use of PDT of cell incubation with MB for I hour then photoirradiation with diode laser and PDT of cell incubation with photopherin for I hour then photoirradiation with He:Ne laser. Aowcytometer (FCM) was more sensitivite than the light microscope in detecting the decrease in cell viability, it also helped in determining the mode of cell death weather apoptosis, necrosis or combined apoptosis and necrosis. Apoptotic cell percentage was higher in PDT of MB and Diode laser or photopherin and He:Ne laser, treated ALL cells compared to untreated ALL cells after I hour but was significantly lower after 24 hours post irradiation. A significant increase in necrotic, combined necrotic and apoptotic cell percentages either measured I hour or 24 hours post PDT, compared to untreated ALL cells and PDT treated normal cells. Electron microscope helped in detecting early cellular apoptotic changes occurring in response to different therapeutic modalities used in this study. In conclusion, PDT proved to be an effective clinical modality in decreasing the number of leukemic cells when irradiated in vitro with appropriate laser and photosensitizer system. Both PDT systems used in this study were efficient in inducing cell death of leukemic cells compared to untreated leukemic cells. However, photopherin PDT system was more efficient in decreasing the cell viability. A significant decrease in viability percentage was detected when studying the effect of PDT on leukemic cells compared to that on normal cells. This suggests that PDT when applied clinically will selectively differentiate between leukemic cells and normal cells, offering a successful component in ALL therapy.

1- Introduction: Photodynamic therapy (PDT) has opened a new field in the treatment of malignancies. The PDT is based on the administration of photosensitizing drugs that are taken by and/or retained in tumour cells to a higher extent compared to normal cells. This procedure requires exposure of cells or tissues to photosensitizing drugs followed by irradiation with light of appropriate wavelength and compatible with the absorption spectrum of the drug or photosensitizer (24). Upon absorption of photon, the photosensitizer undergoes one or more energy transitions and usually emerges in its excited triplet state. The triplet state can participate in a on electron oxidation-reduction reaction (type I photochemistry) with a neighboring molecule, producing free radicals intermediates that can react with oxygen to produce peroxy radicals and various reactive oxygen species (ROS). Alternatively, the triplet state photosensitizer can transfer energy to ground state oxygen (type II photochemistry) and generate singlet molecular oxygen (25). Singlet oxygen was reported to trigger an apoptotic pathway by releasing cytochrome c from the mitochondria via the peroxidation of mitochondrial components and results in cell death. This cell death is different from typical apoptosis because of the abortive apoptotic pathway caused by impaired caspase activation (29). Most photosensitizers for PDT are efficient producers of singlet oxygen in simple chemical systems that type I photochemistry is the dominant mechanism for PDT in most circumstances in cells and tissues (9). Among the many classes of compounds that have been tested as photosensitizers, cationic dyes seemed to be especially

237 promsing. It was shown that many of these dyes penetrate plasma and mitochondrial membranes and can be concentrated up to 1000 fold in mitochondria (22). In the vast majority of applications, the primary role of PDT is to kill unwanted cells or tissues. Cell death caused by PDT (through the generation of reactive oxygen species) can occur either by apoptosis (interphase death or as a secondary event following mitosis) and/or necrosis depending on the cell type, concentration and intracellular localization of the sensitizer, and the light dose (11). The term apoptosis was introduced in 1972 (19). Apoptosis is a tightly regulated process of cell suicide. It is controlled by both intracellular and extracellular signals, terminating in a characteristic sequence of morphological and biochemical changes. It is characterized by systemic dismantling of the cell and preparation of the residual cell components, known as apoptotic bodies and engulfment by tissue macrophage as or other neighboring cells. This process limits leakage of intracellular material to immediate environment, and thereby prevents tissue inflammation (30). Although PDT can produce apoptosis or necrosis, or a combination of the two mechanisms, in many case it is highly efficient in inducing apoptosis (26). The aim of this study was to elucidate the mechanism encountered by the photosensitizers in treatment of acute lymphoblastic leukemia. Also, to compare the the effect of one dose of Helium: Neon laser, Diode laser and different concentrations of Mythelene blue and photopherin using the light microscope, electron microscope and flowcytometry in the assessment of PDT effect.

2-Materials and methods: A piolet study was done to assess the cytotoxic effect of laser alone and photosensitizer alone on normal PBMC as well as to select the appropriate concentration of the photosensitizer, which can produce photodynamic effect on leukemic cells with the least insult to the normal cells. Blood samples were obtained from 15 normal volunteers and 26 ALL patients. Each sample was divided into: • Untreated cells. • Cells treated with three different types of radiation sources (Diode laser, Helium: Neon laser and Non coherent light). • Cells treated with two different types of photosensitizers (Mythelene blue and photopherin) • Cells treated with photosensitizer then irradiated with light having the appropriate wavelength (methylene blue and Diode laser, photopherin and Helium Neon laser, mythelene blue and non-coherent light, photopherin and non-coherent light). Blood collection and separation: Ten ml of blood was drawn from each patient and the control group, into sterile heparin vacutainer.

238 Isolation of Peripheral blood mononuclear cells (PBMC): Lymphocyte separation from whole blood was carried out on histopaque according to the procedure modified from Boyum, 1968 (3). Incubation with photosensitizers: Cell suspension were treated with 2 types of photosensitizers (Mythelene blue and photopherin) an incubated for 30 minutes and for 1 hour in a humid atmosphere of 5% C02 then washed with RPMI media two times. PDT treatment: Cells are then irradiated at a concentration of 2x 10.6 with sources of laser (Diode laser, Helium:Neon laser and non-coherent light). Irradiation methods: 1- Laser irradiation consisted of 2 types of laser: cells treated with photopherin were irradiated with 35 j/Cm2 by He:Ne laser at a wavelength 632.8 nm, cells treated with Methylene blue were irradiated with 35 j/cm2 by Diode laser at wavelength 650 nm. 2- Non coherent light irradiation consisted of a source of non-coherent light emitted from a halogen lamp with original power of 200 Wand a power density of 30 mW. Irradiation was carried out at a wavelength of 600650 nm by using special filters. Measuring the cell viability percentages was done 1 hour and 24 hours after irradiation.

Viability testing was measured by: 1- Light microscope (Try pan Blue exclusion test): One drop of cell suspension was added to one drop of trypan blue solution on a microscope slide and mixed then examined within 2 minutes under the microscope. Non viable cells were stained by blue color. Percentage of viable cells (nonstained) was calculated. 2- Flowcytometry: By the phosphatidyl Serine Detection™ Kit to measure apoptosis: • Dilute the calcium buffer in dernwater (20x) and store at 4C. • Wash the cells and readjust the cell concentration to 1.5xl0 6 cells per ml in calcium buffer. • Add 10 III Annexin V FITC to 100 III cell suspension. • Incubate for 20 minutes on ice in the dark. • Wash the cells with calcium buffer. • Add 10 III propodium Iodide (PI). • Keep the cells at 4C until ready to be analyzed by flowcytometer. Viable cells are not stained Apoptotic cells exclude PI and express Phosphatidyl stain by green colour. Necrotic cells are permeable to PI, which associates with nuclear DNA and is visible as red fluorescence. 3- Electron microscope examination: The following steps were carried out to prepare the cells for E.M. study:

239 Fixation in aldehyde solution at room temperature for 30 minutes. Subsequently, the cell suspension was centrifuged and the cell pellet was resuspended in phosphate buffer (pH 7.4) and washed 3 times in the same buffer. The cells were post fixed in 1 % osmium tetraoxide in phosphate buffer for 2 hours at 4 C. The cell pellet was then rinsed 3 times in distilled water. Dehydration was accomplished at room temperature using graded series of ethanol (30%, 50%, 70%, 90%, 100% twice, 20 minutes each). The cell pellets were then resuspended in a mixture of equal volumes of ethanol 100% and acetone 100% for 5 minutes, centrifuged and the supernatant was decanted. The cell pellets were resuspended in 100% acetone for another 5 minutes, then centrifuged for 5 minutes. Finally, the supernatant was thrown away. A final step of dehydration with propylene oxide for 15 minutes was performed. Infiltration and Embedding: In order to pack the cells, one drop of the cell suspension was placed in the plastic capsule and centrifuged for 15 minutes at 10.000 g before the final filling with Epon. Polymerization and Ultramicrotomy: The capsule was stripped off by two longitudinal cuts in the capsule with a sharp razor in order to obtain the sample block. The sample block was fixed in the holder of the LKB ultramicrotome. Trimming was done to obtain hyramide with a trapezoid surface having 2 parralel sides. The optimal thickness of ultrathin samples ranged between 60 nm and 100 nm, which were cut with a new glass knife, and a ribbon of the sections was made. The ribbon was split up into 3 or 4 small ones. The sections were then picked up on copper grids. The grids were left to dry on a filter paper in petridish. Staining of the grids, was done by a double staining technique of uranyle acetate 4% followed by lead citrate solution . The sections were then examined using Joel E.M. in each studied case, 500 cells were studied with regards to morphologic properties and apoptotic features in the different cellular components.

3-Results: This study involved 26 cases of acute lymphoblastic leukemia admitted to the NCI and 15 normal volunteers as a control group. The cell viability was measured by two different methods ALight microscope. BFlowcytometer Viability as measured by light microscope: A. Normal peripheral blood mononuclear cells: 1- Untreated normal peripheral blood mononuclear cells (PBMC) :

240 The viability percentage was slightly lower after 24 hours compared to that of the cells initially taken with no statistically significant difference. 2- Non coherent light with either MB or photopherin (applied on normal or leukemic cells) has been shown to be non-effective in the present study. 3- Normal cells irradiated with diode laser alone showed no significant change in cell viability percentage when compared to untreated cases as measured: * 1 hour post irradiation: a mean viability percentage of 9S.74±1.23 vs 97.6±l.S% (p>O.OS). * 24 hours post irradiation: a mean viability percentage of 92.82±IAS vs 96.9± 1.23% (p>O.OS). 4- The viability percentage of normal PBMC incubated with methylene blue (MB) alone or combined with photo irradiation with diode laser was significantly lower than that of untreated cases either measured after 1 hour or 24 hours post incubation (Table 1). There was a significantly lower viability percentage of normal cells incubated with MB and photoirradiated with diode laser compared to normal cells treated with MB alone for either measured after 1 hour or 24 hours post incubation (Table 1). Also there was a significant decrease in viability percentage of normal PBMC incubated with methylene blue (MB) alone or combined with photo irradiation with diode laser compared to cells exposed to diode laser alone. The decrease in viability was more enhanced with increasing the incubation time. - In cells incubated with methylene blue alone, viability percentage was significantly lower in cells incubated for 1 hour compared to cells incubated for only Y2 an hour when measured: * 1 hour post incubation (a mean viability percentage of 83.S±1.43%, for 1 hour incubation, vs 9S±3.21 % for Y2 an hour incubation, p
S- Effect of photopherin on viability of normal PBMC: There was a weak cytotoxic effect on normal cells incubated with photopherin either for 'h an hour or I hour compared to untreated cells (1).

241

6- Cells irradiated with Helium Neon(He:Ne) laser alone showed nonsignificant differences in viability percentage when compared to controls as measured: *After 1 hour (a mean viability percentage of 94.17±1.23 compared to 97.63±1.5%. p>0.05). *After 24 hours (a mean viability percentage of 92.82±1.45 compared to 96.9± 1.75%. p>0.05). 7- Combined effect ofphotopherin and He:Ne laser (PDT) on normal PBMC: There was a significant decrease in viability percentage of cells incubated with photopherin either for \12 an hour or 1 hour and photoirradiated with He:Ne laser Compared to normal untreated cells. The decrease in the cell viability percentage was significantly lower with the use of PDT (photopherin and He:Ne laser) compared to either photopherin alone or He:Ne laser alone. The decrease in viability was more enhanced with increasing the incubation time (Table 1). By using the light microscope, the photodynamic effect of decreasing cell viability was most efficient with the use of PDT of photopherin (I hour incubation) then irradiation by He:Ne laser, measured after 24 hours ( a mean viability percentage of 60.62 ±1.4) (Table I). B- Leukemic peripheral blood mononuclear cells: The same effects reported on normal cells were detected on leukemic cells when comparing different methods used. However a more pronounced decrease in cell viability was detected (Table I). The most efficient ways of decreasing viability of leukemic cells with much less effect on normal cells was the use of: One. PDT of cell incubation with MB for 1 hour then photoirradiation with diode laser. When compared to the effect on normal cells ,there was a significant decrease in the mean viability percentage: • 62.4±2.1% vs. 77.8±1.81%, p
242

Viability as measured by flowcytometer (FCM): Plus the higher sensitivity than the light microscope in detecting the decrease in cell viability, it helped in determing the mode of cell death weather apoptosis, necrosis or combined apoptosis and necrosis. FCM was more sensitive in detecting a statistically significant decrease in cell viability in: *Leukemic cells exposed to diode laser, alone, which showed a significant decrease in mean cell viability percentage compared to that of leukemic untreated cells either, measured: -1 hour post irradiation (a mean cell viability percentage of 86.2±2.2% vs. 79.I±2.3% respectively, p
*A higher statistically significant decrease in cell viability, than that detected by light microscope, was detected especially by the use of PDT of: a) MB I-hour incubation, diode laser photoirradiation and measured 24 hours post irradiation when compared to: Untreated ALL cells, a mean viability percentage of 7.5±1.I% vs. 79.1 ±2.3%, p
FCM in determining mode of cell death in ALL:

*PDT of MB and Diode laser effect on ALL cells: • Apoptotic cell percentage was significantly higher in PDT treated ALL cells compared that obtained after diode laser alone, measured 1 hour (p
243

percentage was obtained on comparing the PDT effect to the use of MB alone measured 24 hours post treatment (p
*PDT ofphotopherin an He:Ne laser effect on ALL cells: • Apoptotic ceil percentage was higher in PDT treated compared to untreated ALL cells after I hour (2.9±O.7% vs. 2.6±O.6%,) but was significantly lower after 24 hours (2.0±0.4% vs. 7.S±O.94%, p
I\)

.p.. .p..

Table 1: The mean cell viability percentages as measured by both light microscope and FCM, comparing ditlerent treatment modalities used , applied to both normal d leukemic cells of the stud 0_· .... ":".1'· ALL cells NormalPBMC Treatment I Mean viability % after I hour Mean viability % after 24 Mean viability % after 24 Mean viability % after I hour I hours hours By light By light By light ByFCM ByFCM By light ByFCM ByFCM I microscope microscope microscope microscope 97.6± 92.4± 2.5 96.9± 1.75 87.3±2.4 95.8± 1.5 90.S± 3.1 92.9±1.83 79.1±2.3 Untreated cells 1.5 89.1±2.S 92.82± 93.6± 86.2± 2.2 88.8± Cells treated with 95.74± 82.8±2.6 74.98±2.3 1.45 1.8 1.23 23 diode laser 77.95±1.81 74.7± S2.6± 6 Cells treated with 83.5± 78.6±2.S 73.2±2.S 65± 29.2± 1.5 4.2 1.43 2.4 MB (1 hour incubation) 77.8±1.81 6S.9± 2.1 66.6±1.4 S6.4± 2.9 62.4± 36.1± 2.4 17.4±2.6 7.S± 1.1 Cells treated with 2.1 MB (1 hour incubation)+ diode laser (PDT) 94.2± 90.2± 92.8± 8S.9±2.8 92.4± 83.6± 89.3± 61.2± Cells treated with 1.23 1.45 2.3 2.0 1.8 2.3 He:Ne laser 2.5 81.2± 65.9± 78.6± 4S.S± 61.1± 26.0±1.S Cells treated with 70.1± 63.0±1.9 1.81 4.2 1.43 2.1 2.4 6.0 photopherin (I hour incubation) 60.6± 49.S± 46.2± 30.1± 13.1± 6.8± Cells treated with 74.6± S8.9± 1.4 2.1 2.6 photopherin 1.81 2.5 2.3 1.0 2.2 (1 hour incubation) +He:Ne laser (PDT)

245 Table 2: ApoplOtlC , Necrotic, combined necrotic and apoptotic mean cell percentages as measured by FCM, l'olllparing ditICrent treatment modalities used, applied to both normal and leukemic cells of the study group.

Treatment Untreated cells

NormalPBMC % after 24 hour hours 3.4+1.8 6.0+1.9

% after I

*Apoptosis *Necrosis *Combined

ALL cells % after I

% alier 24

hour 2.6±O.6

hours 7.S±O.9

1.3±fJ.2

2.1 ±fJ.8

2.9±l.4

4.4±l .8

2.9±O.6

S.4±1.4

4.0±1 .2

9.1±O.6

* ~poJllosis *Necrosis *Combined

3.9+1.7

2.3±O.9

3.0±O.83

2.8±1.3

3.4±l.O

5.0±l.8

3.0±l.1

7.7±l1.0

3.8±O.6

9.9±O.6

7.9±1.1

17.6±O.9

*Apoptosis *Necrosis *Combined

11.0±1.3

3.7±1.7

3.S±O.S

1.8±fJ.4

3.0±fJ.5

16.1±2.0

8.6±1.2

20.0±2.5

27.8±1.8

2.8±O.7 27. 7±1.2 40.3±1.4

*Apoptosis *Necrosis *Combined

8.8±O.S 1. 7±fJ. 7 23.5±I.S

1.6±O.7

3.6±O.9

2.9±fJ.7

20.8±2.2

39.0±2.8

39.5±1.3

Cells treated with He:Ne laser

*Apoptosis *Necrosis *Combined

4.I±O.2

I.O±O.4

1.7±fJ.6

2.9±fJ.6

4.0±2.0

11.0±1.6

4.9±O.8 4.1 ±1.3 6.8±O.8

Cells treated with photopherin (I hour incubation) Cells treated with photopherin (I hour incubation) +He:Ne laser

* Apoptosis *Necrosis *Combined

7.8±O.7

3.0±O.9

1.6±fJ.4

2.3±fJ.4

20.S±1.9

31.6± 1.3

Cells treated with diode laser

Cells treated with MB (1 hour incubation) Cells treated with MB (I huur incubation)+ diode laser

4.4±O.S 29.1±1.4 59.1±1.2

(PDT)

(PDT)

*Apoptosis *Necrosis *Combined apoplosis & necrosis

2.0±O.S 12.3±2.8 39.4±5.3

S.O±O.S 10.6±2.7

23.8±1.3 4.4±O.9 26±l.5

50.6±2.7

4.I±O.4

6.I±O.4

2.9±O.7

2.0±O.4

2.4±fJ.4

3.4±fJ.4

1l.7±3.5

16.0±2.3

34.2±1.3

41.2.7

55.2±2.0

74.5±I.7

246 Fig 1:

Electron micrograph of a lymphoblast from a case of ALL with no apoptotic changes (x4600)

Electron nucleus and condensation of the heterochromatin indicating late apoptotic changes after PDT (x3600)micrograph from a case of ALL

247 4-Discussion: Leukaemias are a group of neoplastic disorders characterized by the accumulation of malignant cells in blood and bone marrow. These abnormal cells induce bone marrow failure and infiltrate organs such as liver, spleen, lymph nodes, brain, skin or testis causing undesirable symptoms (12). One of the most common type of leukamias is acute lymphoblastic leukemia (ALL). It accounts for approximately 30% of childhood cancer (38). Aggressive therapeutic modalities using high doses of chemotherapy and/or radiation therapy are now common place treatments for ALL. However, although those methods are effective in most of the cases, they have serious deleterious side effects such as fatigue, malaise, anorexia, nausea, vomiting, low blood counts, erythema, edema, desquamation of skin, increased susceptibility to infection (16). Accordingly, new therapeutic modalities characterized by lower incidence of side effects are required. Photodynamic therapy (PDT) with non-coherent light or laser radiation opens a new field in the treatment of malignancies. In the present study the photodynamic effects of for different PDT were evaluated. The four systems were methylene blue with either diode laser or non coherent light and photopherin with either He:Ne laser or non coherent light. Such systems were applied in vitro on normal and acute lymphoblastic leukemia cells. Both light microscope and flowcytometer were applied to reveal the viability percentage. The mode of cell death, whether apoptosis, necrosis or combined apoptosis and necrosis was further revealed by flowcytometer. Electron microscope was used in selected cases to detect early cellular apoptotic changes. Non coherent light with either MB or photopherin has been shown to be non-effective in the present study. However previous studies reported noncoherent light efficiency in inducing cytotoxicity in non-melanoma skin cancer (4).

With the use of diode laser alone, flowcytometeric analysis has detected a significant decrease in viability percentage of leukemic cells compared to normal irradiated cells after I-hour post irradiation with diode laser, which was more enhanced after 24 hours. However this effect was significantly low compared to leukemic cells treated with MB and irradiated with diode laser. The fact that malignant cells are more affected by diode laser exposure compared to normal cells has been previously explained by Karu, 1999 (18). He reported that cells in the Redox State respond indifferent than normal cells. Renner et aI., 2003 (31) has reported that malignant cells are in the Redox State. In this study, diode laser was used at a fluency of 35 J/cm, which is less in magnitude than

248 previously used fluencies {50 J/cm, 100 J!cm, (28)}. However those higher fluencies had more inhibitory effects on normal cells. The present study has incorporated MB as a photosensitizer because it is a well known dye in medicine. It is an easily applicable drug, has the capability of generating singlet oxygen (32). It was also suggested that MB have the advantage of being both multi drug resistance reverser and a photodynamic agent (36). MB is a potential photonuclease (23), and being a cation, it is selectively absorbed by the mitochondria of tumour cells (21) and potentially trapped by Iysosomes (43). As a lipophilic substance, MB can accumulate in the mitochondrial membranes, thereby altering membrane properties and/or the mitochondrial membrane potential. Photosensitizers that bind to mitochondria induce apoptosis upon photoirradiaion, whereas those that bind to the plasma membrane or Iysosomes, kill cells less efficiently and by a non apoptotic mechanism (27). Therefore, studying the photodynamic effects of MB sensitized with diode laser on both apoptosis and necrosis in leukemic cells under investigation was necessary. In the present study, incubation with MB was significantly cytotoxic in leukemic cells compared to normal cells. This result taken together with previous reports that MB is toxic for neonates, whose cells are actively dividing (1), suggest that activation and differentiation are two important parameters determining cytotoxicity of MB. This latter suggestion recommends the use of MB as a photosensitizer. When applying the PDT (of MB and diode laser) in this study, it was evident by both light microscope and FCM studies that there was a significant decrease in viability percentage of leukemic cells compared to normal cells. Also the decrease in viability, of either normal or leukemic cells, was more enhanced with increasing the incubation time with MB. These results provide further proof to previous studies, which showed that the plateau cytotoxicity curve could be achieved after staining for 90 minutes compared to 30 minutes by MB under the same illumination time (41). Thus indicating that the cytotoxic efficacy was closely related to time of stain and illumination intensity (39). The other PDT system examined in this study was that of photopherin and He:Ne laser. It was evident by both light microscope and FCM that He:Ne laser alone at a fluency of 35 J!cm 2 induced a significant decrease in viability percentage of leukemic cells after I hour post irradiation with He:Ne laser, which was more enhanced after 24 hours compared to their level without treatment. The effect was also more pronounced in irradiated leukemic cell compared to normal cells, which was previously explained that cells in the Redox state respond more than normal cells. He:Ne laser at a fluency of 35 J/cm 2 was less in magnitude compared to previous studies, which used 100 J!cm 2 (18). Photopherin is a partially purified haematoporphyrin derivative (HpD), which have the ability to selectively accumulate in tumour tissues, and to persist there for long periods of time. This property along with the well described photophysical and photosensitizing properties of porphyrin type molecules, has

249 led to their successful use as adjuvants and sensitizers in PDT (17,20). The porphyrin photosensitizers have recently received Food and Drug Administration approval for PDT treatment of oesophageal and endobronchial carcinomas (9,37). Research is also undergoing clinical evaluation for the treatment of bladder, head and neck, brain, intrathoracic and skin malignancies (20). Photopherin emission spectrum was demonstrated in a hydrophilic phosphate buffered saline and in lipophilic liposomal enviroinment to be in the red emission region. Maximum spectra ranged from 615 nm in buffer solution to 635 nm in lipid (7). Accordingly He:Ne laser was our choice of laser since its wave length is 632.8 nm. In the present study, individual incubation with photopherin was more cytotoxic to ALL cells compared to normal cells. This selectivity in killing tumour cells is due to the fact that tumour cells selectively retain photoperin following its uptake, while normal cell clearance for photopherin is more efficient. This dark toxicity for tumour cells have been reported previously by several other studies (5, 10, 15). Therefore, the significant decrease in viability percentage of leukemic cells incubated with photopherin compared to normal cells incubated with photophrin observed in the present study, suggests that photopherin when applied clinically will selectively differentiate between leukemic cells and normal cells. This offers a successful component in A PDT system. Light microscope and FCM studies demonstrated that photopherin at the studied concentration (1 0·4M) induced a significant decrease in viability percentage of leukemic cells after I hour post incubation with photopherin, which was more enhanced after 24 hours compared to their level without treatment. Previous studies have proved the efficacy of this PDT system in vitro and in vivo (14, 34, 35). In this study, flowcytometry was carried out in adjunct with light microscope in order to reveal the mode of cell death, weather it is apoptosis, necrosis or combined apoptosis and necrosis. Although PDT can produce apoptosis or necrosis or a combination of the two mechanisms, however in many cases it is mostly efficient in inducing apoptosis. This property implies that lower doses than those needed to produce necrosis are very effective in producing the desired cell killing results. During apoptosis, cell undergoes a non-necrotic cellular suicide that, in contrast to necrosis, generally does not produce inflammation and injury in the tissue. Apoptotic cells are engulfed by tissue and blood macrophages (26, 27). Cells undergoing apoptosis typically show DNA fragmentation , condensation of chromatin, membrane blebing, cell shrinkage and finally disassembly into membrane enclosed vesicles. A hallmark of this type of cell death is the fragmentation of nuclear DNA into multiples of 200 base pairs through the activation of endogenous nucleases that cleave the DNA between nucleasomes (2). In the present study, when applying Diode laser alone, the predominating mode of cell death was combined apoptosis and necrosis. This could be explained by the fact that leukemic cells are in the Redox state and have

250 an increased production of reactive oxygen species (6). Applying laser will induce a synergistic effect and cause both apoptosis and necrosis. When using PDT of MB and Diode laser, apoptotic cell percentage was significantly higher in PDT treated ALL cells compared that obtained after diode laser or MB alone, measured 1 hour post incubation. Apoptotic cell percentage was also significantly higher in PDT treated compared to untreated ALL cells after 1 hour but was significantly lower after 24 hours post irradiation. This is consistent with the previous reports that the cytotoxic effect induced by MB phototherapy is initiated in the cell membrane and intracellular mitochondria in the early phase, thus causing apoptosis. Consequently, it induce photodamage to microtubules and cause cleavage and cracking of the cell membrane with ribosomal lysis causing combined necrosis and apoptosis (33,40). When applying PDT of photopherin an He:Ne laser, there was a significant increase in necrotic, combined necrotic and apoptotic cell percentages measured 24 hours after PDT compared to that measured after 1 hour. Combined killing with photopherin PDT by both apoptosis and necrosis was previously reported to be induced in human prostate carcinoma cells, human non small cell lung cancer, and rat mammary carcinoma (13) and in lymphoma and epithelial cell (42). It was suggested that, photopherin PDT exhibits early morphgological changes of apoptosis, but the damage of plasma membrane renders the death more necrosis like (14). This in accordance with previous studies that reported combined killing with PDT, using photopherin by apoptosis and necrosis (8, 13). S-Conclusion: • On comparing different photosensitizers used in this study, PDT proved to be an effective clinical modality in decreasing the number of leukemic cells when irradiated in vitro with appropriate laser and photosensitizer system. • Comparing the two PDT systems applied, it is clear that both systems were efficient in inducing cell death of leukemic cells compared to untreated leukemic cells. However, photopherin PDT system was more efficient in decreasing the cell viability. • A significant decrease in viability percentage was detected when studying the effect of PDT on leukemic cells compared to that on normal cells. This suggests that PDT when applied clinically will selectively differentiate between leukemic cells and normal cells. This offers a successful component in ALL therapy. • Flowcytometer was more sensitive in detecting percentage of cell death. It also helped in detecting the mode of cell death. So it is better used to monitor response to PDT during ALL therapy. • Also electron microscope is important to detect early apoptotic changes. • Although PDT can produce apoptosis, necrosis or a combination of the two mechanisms, however in many cases it is mostly efficient in inducing apoptosis. So the use of lower doses than those needed to produce necrosis is recommended

251

to produce the desired cell killing results with less damage to the surrounding tissue.

References: I-Albert M, Lessin M. and Gilchrist B. : Methylene blue: dangerous dye for neonates. J Pediatric Surg. Aug;38(8): 12441245.2003 2-Ball DJ, Luo Y, Kessel D, Griffiths J, Brown SB, Vernon DI: The induction of apoptosis by a positively charged methylene blue derivative. J Photochem Photobiol B. Feb;42(2): 159-163., 1998. 3-Boyum, A:Isolation of mononuclear cells and granulocytes from human blood. Scan. J. Clin. Lab. Invest:21, SuppI.97., 1986. 4-Brown S : The role of light in the treatment of non melanoma skin cancer using methyle aminolevulinate. J Dermatolog Treat.;14 (Supplement 3): 1114.,2003. 5-Chapman JD, Stobbe CC, Arnfield MR, Santus R, McPhee MS : The effectiveness of short term versus long term exposures to photopherin II in killing light activated tumour cells. Radiat Res. Oct; 128(1 ):82-89.,1991. 6-Chilicia K, Los M, Shultz-Osthoff, Gazzalo L, Schirrmachter K,:Redox events in HTLV-1 Tax induced apoptotic T-cell death antioxid Redox signal. Jun; 4(3):471-477. Review.2002. 7-Chwilkowska A., Saczka J, Modrzycka T, Marcinkowska A, Malarska A, Bielewicz J: Uptake of photopherin II, a photosensitizer used in photodynamic therapy by tumour cells in vitro. Acta Biochem Pol; 50(2):509-513.,2003. 8-Dellinger M :Apoptosis or necrosis following photopherin photosensitization: influence of the incubation protocol. Photochem. Photobiol. Jul;54(l): 182187.,1996. 9-Dougherty TJ., Gomer C.J., Henderson B.W., Jori G., Kessel D., Korbelik M., Moan 1., Peng Q. Photodynamic therapy. J.Natl.Cancer Inst.,90:889-905.,1998. lO-Gomer CJ, Rucker N, Murphree AL.:Differential cell photosensitivity following porphyrin photodynamic therapy. Cancer Res. AugI5;48(16):45394542.1998. 11- Gupta S, Dwarakanath BS, Muralidhar K, Jain V:Role of apoptosis in photodynamic sensitivity of human tumour cell lines. Indian J Exp BioI. Jan;41(l ):33-40.,2003. 12-Hasse D, Feuring-Buske M and Konemann S. :Evidence for malignant transformation in acute myeloid leukemia at the level of early haematopoietic stem cell by cytogenetic analysis of CD34 subpopulations. Blood; 86;29062912.,1995. 13-He XY, Sikes RA, Thomsen S, Chung LW, Jacques SL.:Photodynamic therapy with photopherin II induces programmed cell death in carcinoma cell lines. Photochem. photobiol;59(4):468A73.,1004. 14-Hsieh YJ, Wu CC, Chang CJ, Yu JS.:Subcellular localization of photopherin determines the death phenotype of human epidermoid carcinoma A431 cells triggered by photodynamic therapy when plasma membranes are the main target. J Cell PhysioI.Mar;194(3):363-375.,2003.

252 IS-Jiang F, Chopp M, Katakowski M, Cho KK, Yang X, Hochbaum N, Tong L, Mikkelesen T . Photodynamic therapy with photopherin reduces invasiveness of malignant human glioma cells. Lasers Med Sci .;17(4):280-288.,2001 16-Kalaycio M.:Biologic therapy of leukemia: Matt Kalaycio(editor) Puplisher. Humana Press. ISBN 1-58829-071-9.,2003. 17- Kulka U, Schaffer M, Siefert A, Schaffer PM, Olsner A, Kasseb K, Hofstetter A, Duhmke E, Jori G. :Photofrin as aradiosensitizer in an in vitro cell survival assay. Biochem Biophys Res Commun. Nov 7;311(1):98-103 .,2003. 18-Karu T. :Primary and secondary mechanisms of action of visible to near IR radiation on cells. J. Photochem. Photobiol. B BioI, 491-517.,1999. 19-Kerr A.H., Wyllie and A.R. Currie.:Apoptosis: a basic biological phenomenon with wide range implications in tissue kinetics. Br.J.Cancer (26):239-257.,1972. 20-McCaughan JS.:Photodynamic therapy for endobronchial malignant disease: a prospective fourteen-year study. J.Thorac.Cardiovasc.Surg.,114:940-947., 1999. 21-Mellish KJ, Cox RD, Vernon DI, Griffiths J, Brown SB:In vitro photodynamic activity of a series of methylene blue analogues. Photo chern photobiol.Apr;7 5(4) :392-397 .,2002. 22-Modica N., politano S., Joyal., Ara G., Oseroff A.:Mitochondrial toxcicity of cationic photosensitizer for photochemotherapy. Cancer Res.50:78767881.,1990. 23-Mohammad T., Morrison H.:Photonuclease activity of Taylor's blue. Bioorg Med Chern Lett. Aug 2;9(15):2249-2254.,2002. 24- Neidre M.J., Secord A.J., Patterson M.S ., Wilson B.C.: In Vitro Tests of the Validity of Singlet Oxygen Luminescence Measurements as a Dose Metric in Photodynamic Therapy. Cancer Research 63, 7986-7994, November 15.,2003. 25-0chsner:Photodynamic therapy: the clinical prospective review on applications of control of diverse diseases, Azneim-Forsch., 1997. 26-0leinick N.L. and Evans L.L. : The photobiology of photodynamic therapy: Cellular targets and mechanisms, Radiat. Res., 150,SI46-S156.,1998. 27-0leinick N., Morris R. and Blichenko.:The role of apoptosis in response to photodynamic therapy: what, where, why and how. Photochem. Photobiol. Sci., 1:1-21.,2002. 28-0rth K, Beck G, Genze F, Ruck A. :Methylene blue mediated photodynamic therapy in experimental colorectal tumours in mice. J Photochem Photobiol B. Sep;57(2-3) 186-192.,2000. 29-0tsu K, Sato K, Ikeda Y, Lmai H, Nakagawa Y, Ohba Y, Fujii J.:Abortive apoptotic pathway by singlet oxygen due to the suppression of caspase activation. : Biochem J. Mar 30; [Epub ahead of print]2000. 30-Reed J.e. :Molecular biology of CLL. Semin Oncol. (1).11.,2002 31-Renner K, Amberger A, Konwalinka G, Kofler R, Gnaiger E. :Changes of mitochondrial respiration, mitochondrial content and cell size after induction of apoptosis in leukaemia cells. Biochem Biophys. Acta Sep 23;1642(1-2): 115123.,2003.

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32-Salmenova D, Subbarayan M, Hafeli UO, Feyes DK, Unnuthan l, Emancipator SN, Mukhtar H.A. Simplified method for preparation of 99m Tc-annexin V and its biologic evaluation for in vivo imaging of apoptosis after photodynabmic therapy. 1 NucI Med. Apr; 44(4):650-656.,2002. 33-Stockert lC, luarranz A, Villanueva A, Canete M.: Photodynamic damage to Hela cell microtubules induced by thiazine dyes. Cancer Chemother Pharmacol;39(1-2): 167-169.,1996. 34-Tajiri H, Hayakawa A Matsumoto Y, Yokoyama I, Yoshida S. :Changes in intracellular Ca concentrations related to PDT -induced apoptosis in photosensitized human cancer cells. Cancer Lett. lun 19;128(2):205-210.,1998. 35-Tita SP, Perussi lR.:The effect of porphyrins on normal and transformed mouse cell lines in the presence of visible light. Branz 1 Med BioI Res. Oct;34(10): 1331-1336.,2001. 36- Trindade GS, Farias SL, Rumjanek VM, Capella MA.:Methylene blue reverts multidrug resistance: sensitivity of multidrug resistant cells to this dye and its photodynamic action. Cancer Lett. Apr 14;151(2):161-7.,2000. 37 -Vicente MG.: Porphyrin based sensitizers in the detection and treatment of cancer: recent progress. Curr Med Chern Anti Cane Agents. Aug;1(2): 175194.,2001. 38-Young Y.L. and Miller R.W.:lncidence of malignant tumours in U.S. children. l.pediatr.,86:254-258., 1975. 39-Ya DS, Chang SY, Ma CP.:Photoinactivation of bladder tumour cells by methylene blue:study of a variety of tumour and normal cells. 1 Urol:44(1): 164168.,1990. 40-Ya DS, Chang SY, Ma CP.:Ultrastructural changes of bladder cancer cells following methylene blue sensitized photodynamic treatment. Eur Urol;19(4):322-326.,1991. 41-Ya DS, Chang SY, Ma CP.:The effect of methylene blue sensitized photodynamic treatment on bladder cencer cells: a further study on flowcytometric basis. 1 Urol. May;149(5): 1198-1201., 1993. 42-Zaidi SI, Oleinick NL, Zaim MT, Mukhtar H.:Apoptosis during photodynamic therapy induced ablation of RIF-l tumours in C3H mice: electron microscopic, histopathologic and biochemical evidence. Photochem Photobiol. 1993 Dec;58(6):771-776., 1993.

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MOLECULAR MECHANISMS AND APOPTOSIS IN PDT BARBARA KRAMMER Department of Molecular Biology, University of Salzburg, Hellbrunnerstr. 34, A-5020 Salzburg, Austria E-mail: [email protected] THOMAS VERWANGER Department of Molecular Biology, University of Salzburg, Hellbrunnerstr. 34, A-5020 Salzburg, Austria E-mail: [email protected] Photodynamic Therapy (PDT) is a successful new therapy for malignant and nonmalignant diseases. It is based on the activation of a photosensitizing dye by visible light in the target tissue, followed by production of cytotoxic substances. The article gives a short overview on the field of PDT with main focus on molecular mechanisms and apoptosis. It includes photodynamic principles, clinical application and procedures, biological effects, molecular mechanisms of damage processing and apoptosis.

Introduction

PDT is increasingly accepted as a new tool for the selective destruction of malignant and non-malignant tissue and cells. Although PDT is applied successfully in many countries since 30 years in form of clinical trials, approvals with different photo sensitizers was obtained only in the past few years for selected application fields. PDT is effective, cheap and without severe side effects. It can be used also in cases, where classical therapies fail or crossresistance is present, it can be applied repeatedly, since it is not tumorigenic, and can be combined with other therapies. Principle of PDT

The principle of PDT is that a photosensitizer, light and oxygen work together to cause death (by necrosis or apoptosis) of the target tissue/ cells. Once a photosensitizer is applied, it is in general accumulated selectively in the targets. Itself non-toxic, it can transfer the energy of absorbed light to molecular oxygen or other targets and thus produce reactive oxygen species and other radicals. The activating light of the visible or near infrared spectrum is by itself harmless too. Since the penetration depth into tissue increases with the irradiation wavelength in this spectral range, also the spectral properties of the sensitizers - dependent on their structure composed of extended ring systems - determine the target depth. Under optimal conditions, target cells or tissue are destroyed. 255

256

Clinical Application

The minimally invasive nature and scar-free wound-healing has made PDT a good option for the treatment of skin cancers and other skin disorders. For palliative treatment of invasive cancers, PDT causes less trauma than most other therapies, and it is sometimes the only remaining treatment option. In addition, PDT has proven to be effective under conditions where an increased risk of cancer is present. The main side effect of systemic PDT is skin photosensitization. The patient should avoid bright sunlight for days to weeks. PDT is applied in many clinical disciplines, at inner and outer surfaces, to eliminate malignant and inflammatory tissue, bacteria and other microorganisms. Malignant diseases are treated in the areas of skin, lung, bladder, ear-nose-throat, oesophagus, stomach, cervix uteri, brain, pankreas, brain and prostate. Non-malignant applications are the sterilisation of blood cells, removal of viruses, bacteria and other microorganisms, rheumatic arthritis, arteriosclerosis, macula-degeneration, prophylaxis of restenosis after angioplastic, caries and malaria. Especially in dermatology, actinic keratosis, superficial basaloma, Kaposisarkoma, cutaneous metastases, condyloma, warts, psoriasis, Morbus Bowen, acne and dermatophytic fungi are treated; but it is also used for cosmetic purposes, e.g. skin rejuvenation due to the excellent cosmetic results. Clinical Procedures

Photo sensitizers used are mainly modifications of the body-derived porphyrins, chlorins, artificial phthalocyanines or other substances like the hypericin, an extract from St. John's Wort. Approval was obtained for ALA, the precursor of the endogenously formed protoporphyrin IX and its methyl-ester Metvix®, further for Photofrin® (porphyrin-derivative), Foscan® (chlorin) and Photosense® (phthalocyanine). After the application of a photosensitizer to the patient via different routes (e.g. intravenously, topically, orally), the time point of the optimal, selective accumulation ratio between normal and target tissue or cells is used for irradiation with a wavelength depending on the absorption spectrum of the photosensitizer. The irradiation is carried out with a variety of light sources, such as a dye laser coupled to a fiber optic and specially designed applicators for uniform illumination of body cavities. But also several lamps with filters or LED arrays are used.

257

Biological effects According to its chemical properties, incubation time, concentration and localisation, the activated sensitizer can damage blood vessels, kill directly target cells and stimulate the immune system. In the vascular-mediated tumor treatment an interference with antiangiogenic pathways (Agostinis et a!., 2004, Almeida et aI., 2004) can be observed. Vascular endothelial growth factors (VEGF) - known for a strong mitogenic activity - seems to be up-regulated by oxidative stress. However, lethal PDT causes a vascular shut-down and blood flow stasis (Almeida et a!., 2004 and Krammer, 2001). In the case of direct cell killing, the sensitizer has to enter the cell and to be distributed intracellularly. This localisation and a following redistribution, depending on their part on · several cell qualities and on the incubation parameters, determine the site of damage after irradiation when oxygen is present. Re-diffusion of oxygen to depleted tissue sites can be supported by a light fractionation protocol or a reduction of the power density at the same fluence. An often observed stimulation of immune reactions such as a cytotoxic Tcell response was leading to the conclusion that PDT can be used as tumor vaccine. PDT-generated tumor lysates were found to be effective whole tumor vaccines with tumor-specifity (Gollnick et a!., 2002). The significant therapeutic effect, i.e. tumor cure by an antitumor adaptive immune response, could be proven by Korbelik and Sun (2006) to be induced by heat shock proteins (Hsp70) and complement opsonization (C3) (Korbelik and Sun, 2006). Furthermore the accumulation of the endogenous photosensitizers PpIX in macrophages and dendritic cells (Hryhorenko et a!., 1998) suggest that sensitizer loaded immune cells could contribute to the supply of tissues with the photosensitizer. Direct modulation of signalling pathways and interaction with single molecules can also be found after PDT (Agostinis et a!., 2004.), be it in a transient way as in the case of sublethal PDT (Verwanger et a!., 1998). Molecular Mechanisms of Damage Processing After activation of the photosensitizer, the primary mechanisms are the production of radical oxygen species and other toxic substances. The cells react by activating the antioxidant defence system including reduced glutathion (Kiesslich et aI., 2005). If the primary damage to mainly proteins and lipids cannot be prevented, the repair system will be mobilized on the molecular biological level.

258 However, the intracellular targets (cellular membrane, ER, lysosomes, mitochondria) of the phototoxic action are the starting points of different pathways of damage processing leading finally to cell death via apoptosis or necrosis, if the repair system cannot stop or neutralize the damage in advance. On the way to the endpoints quantity and quality of the damage and the cell sensitivity playa crucial role. This can be modulated by several factors, such as cell protection effects (e.g. by increase of Ca2+, heme oxygenase, heat-shock proteins (Hsp», alteration of energy supply or of signaling pathways. Changes of the major MAPKs pathways and their downstream targets such as cyclooxygenase-2 (COX-2) were detected after PDT (activation of p38 MAPK and INKs and inhibition of ERKs by hypericin- and ALA-PDT). COX-2 was up-regulated by PDT, but also found to suppress PDT-effects (Agostinis et aI., 2004 and Almeida et aI., 2004). Our own results showed - in accordance with the literature above upregulation of Hsp-70 and heme oxygenase-1 (HO-1; for damage protection), and of c-jun and c-fos (stress response) 3 hrs after ALA-PDT with LD 25 and cell death by necrosis (Veiwanger et aI., 2002 ); further the induction of c-fos and cjun, and decreased expression of genes involved in cell proliferation (c-myc), apoptosis (FADD) and cell attachment (fibronectin) 1.5 - 8 hrs after ALA-PDT with LD60 and 30% apoptosis (Ruhdorfer et aI., 2007). Significant changes of many genes (out of about 10.000) involved in apoptosis induction, oxidative stress response, proliferation, MAPK and RAS signalling pathways, energy metabolism and cell adhesion could be detected between 1.5 - 8 hrs after hypericin-PDT under the conditions of LDso with 70% apoptosis and 10% necrosis. Apoptosis

The cell death modes and its pathways were investigated in more detail by several groups (Oleinick et aI., 2002). Cell membrane destruction and lack of energy shifts all ongoing processes to necrosis. Apoptosis is carried out mainly by the mitochondrial internal pathways, but also by the receptor-mediated or ER-mediated pathways. The cell death mode in tum influences the immune response as stated above. E.g. the function of macrophages can be shifted from tumor cell kill by interaction with necrotic cells to growth stimulation by apoptotic cells (Reiter et aI., 1999) The mitochondrial pathway is characterized by a cascade of steps leading to the deconstruction of the cell and the formation of apoptotic bodies. It starts with oxidation of the adenine nucleotide transporter in the inner mitochondrial membrane by ROS, changing it to an unspecific pore. Water is taken up to the

259 matrix leading to unfolding of the inner mitochondrial cristae and consequently to the rupture of the outer mitochondrial membrane. This membrane permeabilization results in reduction of the mitochondrial membrane potential, mitochondrial swelling and release of pro-apoptotic factors such as cytochrome c, apoptosis-inducing factor and pro-caspase-9. Assembly of cytochrome c, apoptosis protease activating factor-I, ATP and pro-caspase-9 in form of an apoptosome has the purpose to activate the initiator caspase-9. Activated caspase-9 activates in turn the effector caspases-3, - 6 and -7, which are responsible for executing the apoptotic program by cleavage of cellular proteins due to their endoprotease activity. Also the DNA is fragmented to equal pieces of about 200 base pairs by endonuclease activity. The deconstruction process leads to nuclear fragmentation and formation of apoptotic bodies ready for uptake and re-cycling by immune and neighbouring cells. The receptor-mediated or external pathway uses the initiator caspase-8 or -2 to activate the effector caspases, either directly or via the mitochondrial pathway. Regulatory proteins of the Bcl-2 family with pro- and antiapoptotic family members interact with components of the apoptotic pathways at several steps: they are involved in mitochondrial pore opening and activation of caspases. Not only ROS directly, but also several other members of intracellular pathways or second messengers such as intracellular calcium, cathepsins, ceramides, arachidonic acid metabolites or cyclic nucleotides can play a prominent role in the cytotoxic action of PDT.

References:

Agostinis, P., Buytaert, E., Breyssens, H. and Hendrickx, N. (2004) "Regulatory pathways in photodynamic therapy induced apoptosis", Photochem Photobiol Sci., 3(8): 721-9. Almeida, R.D., Manadas, B.l., Carvalho, AP. and Duarte, C.B. (2004) "Intracellular signaling mechanisms in photodynamic therapy", Biochim Biophys Acta., 1704(2): 59-86. Gollnick, S.O., Vaughan, L. and Henderson, B.W. (2002) "Generation of effective antitumor vaccines using photodynamic therapy", Cancer Res., 62(6): 1604-8. Hryhorenko, E.A, Oseroff, AR., Morgan, 1. and Rittenhouse-Diakun, K. (1998) "Antigen specific and nonspecific modulation of the immune response by aminolevulinic acid based photodynamic therapy", Immunopharmacology, 40(3):231-40.

260 Kiesslich, T., Plaetzer, K., Oberdanner, C.B., Berlanda, J., Obermai,r FJ. and Krammer, B. (2005) "Differential effects of glucose deprivation on the cellular sensitivity towards photodynamic treatment-based production of reactive oxygen species and apoptosis-induction", FEBS Lett. 579(1): 18590. Korbelik, M. and Sun, J. (2006) "Photodynamic therapy-generated vaccine for cancer therapy", Cancer Immunollmmunother., 55(8):900-909. Krammer, B. (2001) "Vascular interactions of Photodynamic Therapy", Anticancer Res., 21: 4271-4278. Oleinick, N.L., Morris, RL. and Belichenko, I. (2002) "The role of apoptosis in response to photodynamic therapy: what, where, why, and how", Photochem Photobiol Sci. ,1(1): 1-21. Reiter, I., Krammer, B. and Schwamberger, G. (1999) "Cutting edge: differential effect of apoptotic versus necrotic tumor cells on macrophage antitumor activities", I Immunol., 163(4): 1730-2. Ruhdorfer, S., Sanovic, R, Sander, V., Krammer, B. and Verwanger, T. (2007) "Gene expression profiling of the human carcinoma cell line A-431 after 5arninolevulinic acid-based photodynamic treatment" Int. 1. Oncol., 30 (5): 1253-62. Verwanger, T., Schnitzhofer, G. and Krammer, B.(1998) " Expression kinetics of the (proto)oncogenes c-myc and bc1-2 following photosensitization of human normal and transformed fibroblasts with 5-aminolevulinic acidstimulated endogenous protoporphyrin IX", I Photochem. Photobiol, B:Biology,45: 131-135. Verwanger, T., Sanovic, R, Aberger, F., Frischauf, A.-M. and Krammer, B. (2002) "Gene expression pattern following photodynamic treatment of the carcinoma cell line A-431 analysed by cDNA arrays", Int I Oncol., 21 (6): 1353-1360.

Acknowledgements: The work was supported by research grants from the Austrian FWF, Nr.: P15143 and P17058

FOLLOW UP OF TREATMENT OF CADMIUM AND COPPER TOXICITY IN CLARIAS GARIEPINUS USING LASER TECHNIQUES KHALID H. ZAGHLOUL Faculty of Science Zoology Dept., El-Fayoum University MAHA F. ALI and MANAL G. ABD EL-BARY National Institute of Laser Enhanced Sciences, Dept. of Medical and Biological Applications., Cairo University MOHAMED ABD El-HARITH National Institute of Laser Enhanced Sciences, Dept. of Environmental, photochemistry and Agricultural, Cairo University

Two purified diets were formulated and fed to seven groups of the Nile catfish; Clarias gariepinus for 12 weeks. The formulated diets contained 50 or 500 mg/kg diet of an ascorbic acid equivalent, supplied by L-ascorbyl-2-monophosphate (Mg salt). Laser induced breakdown spectroscopy (LIDS) technique has been used to characterize the bioaccumulation of cadmium, copper and iron in some selected organs (Gills, liver, kidney and muscles) and disturbance in the distribution of sodium, calcium and magnesium in gills and muscles of fish fed the minimum requirement of vitamin C (50 mg/kg diet) and exposed to cadmium (0.165 mg/I) and copper (0.35 mg/I) individually or in combination. Heavy metals bioaccumulation affect histological structure of gills, liver and kidney and consequently, fish exhibited the lowest growth rate and meat quality with a progressive fall in RBCs count, Hb content and haematocrite value. These effects were concomitant with significant increase in the WBCs count, serum glucose, total protein, AST, ALT, creatinine and uric acid. On the contrary, serum total lipids and liver glycogen revealed a significant decrease. However, fi sh fed 500 mg vitamin C/kg diet and exposed to the same concentrations of cadmium and copper either individually or in mixture showed an improvement in the growth rate and meat quality and a tendency to exhibit close to the control values for most of the other studied physiological , biochemical and histopathological investigations.

1. Introduction

Pollution of the aquatic environments with heavy metals has become a more serious concern during the recent years. The loading of metals resulting from industrial and agricultural discharges into our environments creates water pollution problems due to their toxic effect on aquatic biota (Zaghloul et al., 2000 and Elghobashy et al., 2001). In addition, metal ions can be incorporated into food chain and cncentrated by fish to a level that affects their physiological 261

262 state and hence become a threat to man (Haggag et aI., 1999; and Elghobashy et al., 2001 and Sharaf, 2004). Essential trace elements have a narrow optimal concentration rang for growth and reproduction, and both excess and shortage can be detrimental to organisms (Pelgrom et aI., 1994), with unusually high concentration becoming toxic to aquatic organisms (Wepener et aI., 2001).Other metals (for example cadmium and lead) have no known biological function (Seymore,1994). Certain of these non-essential trace metals, for example cadmium, are major contaminants of aquatic environments that are toxic towards aquatic organisms (Witeska et al., 1995) even at concentrations found in natural water (Pelgrom et al., 1994). However, aquatic toxicants never occur singly but always as a mixture. If tow or more metals are present in the aquatic ecosystem, they may exert a combined effect on fish which is additive. They may interfere with one another (antagonism)or their overall effect on an organism may be greater than when acting alone (Sorensen, 1991; Salah El-Deen et ai., 1995 and Zaghloul and El-Kholy, 2002). In last years, the LIBS (Laser Induced Breakdown Spectroscopy) technique has become available method for fast qualitative or semi-quantitative analysis of material. A number of applications have been proposes in many different fields, ranging from cultural Heitarge studies, industrial process control, bio-medical applications, etc. (Ciucci, et aI., 1996 and Corsi, et al., 2000). The initiation and drive for the use and development of LIBS has been due to the need for direct and rapid determination of trace elements in various types of samples, particularly metals. This is because no other technology can do trace determination as efficiently as LIBS without complicated sample preparation (Sneddon and Lee, 1999). So the aim of the present study is to follow up the effect of vitamin C as antioxidant in inhibiting the toxicity of cadmium and copper and their bioaccumulation in the Nile catfish; Clarias gariepinus tissues using Laser Induced Breakdown Spectroscopy (LIBS). 2. Materials And Methods Healthy fish of Nile catfish; Clarias gariepinus weighing approximately 50 g/fish were collected from Elzawida fish farm, Kaluebqa Governorate, Egypt. Fish were transferred to laboratory and acclimated for 2 weeks in large tanks with well-aerated dechlorinated tap water at a temperature (25±1°C). The pH was 7.3± 0.2 and oxygen content was 7.2 mg/l that was maintained constant using air pump.

263 2.1 Determination of LC so : Toxicity tests were carried out on the Nile catfish; Calarias gariepinus (50 g/fish approximately) for cadmium and copper according to Litchfield and Wilcoxon (1949). The tests showed that, the 96 hr LC so values of the Nile catfish; Clarias gariepinus were 16.5 mg/I for cadmium and 3.5 mg/I for copper at 90 ppm CaC03 hardness. 2.2 Diet formulation: A basal diet was formulated according to Abdel-Ghany(1996). All diets were formulated to contain 32% crude protein. L-ascorbyl-2-phosphate was added to the basal diet on an equimolar ascorbic acid basis at 50 and 500 mg vitamin Clkg diet. Phosphate ester of ascorbic acid in the form of monophosphate has been found to be more stable than the acid form, highly available and effectively utilized by channel catfish; Ictahurus Punctatus as a vitamin C source for growth (Lovell and EI- Naggar, 1989 and EI-Naggar and Lovell, 1991). The dry components of the diet were mixed in a Hobart mixer. Water and oil were added to obtain a soft paste. The paste was passed through a mincer and dried at 35°C in a forced air circulator. Pellets were crumbled to appropriate size, screened and fed to the fish. The bulk of the diets was kept at -18°C.A small amount of each diet, corresponding to the weekly requirements, was kept in a refrigerator for weighing daily amounts and renewed each week. In order to follow the effect of the sublethal concentrations (1/10 LC so) of cadmium individually and in mixture with copper at two levels of ascorbic acid formulated diet (50 and 500 ascorbic acid/ kg diet). Fish were divided into seven groups (10 fish each), distributed in glass aquaria of 120 liter capacity at a rate of 8 fish/aquarium. Dechlorinated tap water was used thought the study in order to avoid metabolite accumulation, the aquaria of water was changed daily. 2.3 Studied groups: Group I : Control group, fish fed diet containing 50 mg ascorbic acid/ kg diet. Group II : Fish were exposed to 1.65 mg Cd/I and fed diet containing 50 mg ascorbic acid/kg diet. Group III: Fish were exposed to 0.35 mg Cull and fed diet containing 50 mg ascorbic acid/kg diet. Group IV: Fish were exposed to mixture of Cd (1.65 mg/I)and cu (0.35 mg/I)and fed diet containing 50 mg ascorbic acid Ikg diet. Group V : Fish were exposed to 1.65 mg Cd/I and fed diet containing 500 mg ascorbic acid/kg diet. Group VI : Fish were exposed to 0.35 mg Cull and fed diet containing 500 mg ascorbic acid Ikg diet.

264 Group VII : Fish were exposed to mixture of Cd (1.65 mg/l) and Cu ( 0.35 mg/l) and fed diet containing 500mg ascorbic acid / kg diet. The duration of the experiment was three months from June to August at temperature 25±I°C and oxygen content was maintained at 7.3 ± 0.2 mg/l using air pump. Fish were fed at a rate of 3% of live body weight with polluted fish diet (32% protein) twic daily. Fish were weighed every two weeks to measure the growth and to adjuct the feed amounts. At the end of the experiment (12 weeks) blood samples were drawn then fish were sacrified for obtaining organs samples of fish were subjected to chemical analysis. (1) Growth parameters Body weights were recorded to the nearest gram and total body lengthe were measured to the nearest 0.1 cm for the fish in the different studied groups, to adjust the artifical feed rate, till the end of the experimental period (12 weeks) where the following growth indices were determined. Specific growth rate: Specific growth rate (growth rate/day) was determined as a percentage of body weight gain/day according to the equation postulated by Allen and Wooton (1982): S.G.R.= Ln Wf-Ln Wo X 100 Tf -

Where: Wf : The final weight of fish in g.

To

/

Wo:

The initial weight of fish

in g. (Tf - To): Time between the final and initial weight in days. / Ln : Logarithm to base. Mean cumulative growth: Mean cumulative growth was determined as percentage of body weight gain to the initial wet weight. Condition factor (k): K factor was calculated for individual fish from the formula recommended by Schreck and Moyle (1990): K= W X 100 L3 Where: W : is the wet weight in g . / L : is the total length in cm. (2) Biochemical analysis

(A) Serum analysis: Blood samples were centrifuged at 3000 r.p.m. to get serum for the following analysis: Serum glucose: according to Trinder (1969, Serum total protein: by Biuret test (King and Wootton, 1959), Serum totallipids:by hovanillin reaction according

265 to Schmit (1964), Serum AST (E.C2.6.1.1.) and ALT (E.C2.6.1.2.) according to the method described by Reitmans and Frankel(1957), Serum creatinine: according to Henry (1974), Serum uric acid: according to Barham and Ttinder (1972). (B)Liver analysis: (I) Hepatosomatic Index (HSI): HSI was calculated as liver percentage to whole body wet weight HIS = Liver Weight (g) X lOa Body Weight (g)

(II) Determination of liver water content: Liver samples were rapidy transfered to a weighting bottles and accurately weighted. The bottles were then placed in drying oven at 105°C for 72 hours (Sidwell et aI., 1970). (III) Liver glycogen: Liver glycogen was determined by the another one methode of Roe and Ealley (1966). (C )Muscle analysis: (I) Muscle water content was determined according to Sidwell et at., (1970). (II)Muscle total protein was determined using the semi-microkjeldahl method as reported by Josyln (1950). (III)Muscle total lipids was determined by the standard method reported in A.O.A.C(1970). (IV)Muscle ash was determined by burning the samples in a muffiefurnace for 16 hours at 550°C (Sidwell et at., 1970). (3) Residual heavy metals: Residual heavy metals Cd, Cu, Fe were determined in the gills, liver, kidney and muscles of Ctarias gariepins in addition to some electrolytes (Na, ca, Mg) in gills and muscles using laser induced breakdown spectroscopy (LIBS).according to Sneddon and Lee (1999). The following diagram and table show the main components of the device as well as the conditions at which the work is carried out: Laser pulses from an Nd-YAG laser are focused on the sample. The light emitted from the laser induced plasma is collected in a fiber optics and fed to the edelle spectrometer. The dispersed spectrum is detected by an ICCD (intensified charge coupled device) coupled to the spectrometer. The detained spectra are displayed on the PC for further analysis.

266 (4) Statistical analysis: The results were statistically analyzed using analysis of variance (F-test) followed by Duncan' s multiple range test to determine differences in means (SAS, 2000), 3. Results and Discussion

Scarcity of water resources in many areas all over the world, especially in arid and semi-arid areas has dictated the need for using different water qualities for irrigation purpose. Nowadays, Egypt where the Nile water is almost the only renewable fresh-water resource, is facing a problem of water shortage due to the increased population and limited amount of water (Abdel Rashied et al., 1998). Unconventional waters, like waste municipal water and agricultural drainage water, are the fastest and relatively inexpensive solution to this prevailing crisis. However, fish health may suffer in agricultural drainage and waste municipal waters unless their quality is fully evaluated by chemical analyses to asses the levels of heavy metals that could be incorporated into fish tissues (Zaghloul et al., 200S) and hence become a threat to man (Ajmal et aI., 1985). Heavy metals are widely distributed in aquatic system due to industrial development and the wide use of chemicals in agriculture. They may lead to either an increase or decrease in growth of various fishes and within their permissible level, are essential for food efficiency and growth rate (Glubokov, 1990). However, higher concentration of heavy metals beyond the tolerance limit of fishes affect fish popUlations, reducing their growth, reproduction and/or survival and may even kill fishes (Schreck and Lorz, 1978 and ZaghlouI2000). Pollutant toxicity to aquatic organisms has been measured, in the classical toxicology, by using lethal concentration and determination of LC so , which is the concentration of substance that is estimated to kill SO% of a group of organisms within a specified time period and conditions (Sprague, 1970). The level of LC so appears to be influenced by water quality and species difference. Certain species tend to be less tolerant to high pollutant concentrations than others (Sprague, 1970 and Skea et al., 1987). In the present study, the response of Clarias gariepinus to cadmium and copper toxicity was quit different. It appears that copper is more toxic than cadmium where the 96 hr LC so values were 3.S mg Cull and 16.S mg Cd/I at the same water quality criteria. With the increased risk of heavy metals toxicity, searching for protective agents has drawn a great attention of many investigators (kostyniak and Clarkson, 1981; Ghazaly, 1994; Abdel-Tawwab et al., 2001 and Zaghloul and EI-Kholy, 2002). They reported that, chelation therapy is the most successful modality for the management of heavy metals poisoning. L-ascorbic acid or vitamin C is essential for normal metabolism in animal cells. All vertebrate body tissues contain ascorbic acid in different concentrations according to the tissue

267 and species in question. However, the ability of fish to synthesize ascorbic acid is limited (Ikeda and Sato, 1965), if not absent (Albrektsen et aI., 1988) because they do not posses the enzyme L-gulonolactone oxidase, which, is required for its biosynthesis (Yamamoto et ai., 1978). The inability to synthesize ascorbic acid is not a problem if external sources are provided. Pond-cultured fish reared at low densities normally can obtain sufficient ascorbic acid from natural sources. Natural sources, however, do not supply adequate amounts when fish are reared under high-density culture conditions in ponds, raceways or cages. Thus, fish require a dietary source of vitamin C for normal metabolism and growth (Lovell and EI-Naggar, 1989 and Abdelghany, 1996 & 1998). The formulated diets, in the present study, contained 50 and 500 mg/kg diet of ascorbic acid equivalent supplies by L-ascorbyl-2- mono phosphate (Mg salt). Since, L-ascorbic acid derivatives with sulfate and phosphate moieties at the unstable C 2 position in the lactone ring are highly resistant to heat, storage, oxidation and have shown vitamin C activity for fish (EI-Naggar and Lovell, 1991). The authors reported also that L-ascorbyl-2-monophosphate and ascorbic acid have equimolar ascorbic acid value for growth of channel catfish, but that L-ascorbyl-2-monophosphate is more effective than ascorbic acid for maintaining tissue levels of ascorbic acid. 3.1 Residual heavy metals: Atomic ions as well as neutral atoms are produced in plasma sources having high temperatures. Direct observation of the laser-induced plasma with atomic emission spectroscopy is a simple method for the analysis of the sample and offers the potential of simultaneous multi-element analysis. The energy levels are unique for each element, so it is possible to perform simultaneous qualitative analysis by examining wavelengths in the emission spectrum of an unknown element in the sample. Using the experimental set up explained previously, the plasma was produced using dried samples irradiated with a Q-switched Nd: YAG laser at its fundamental wavelength; 1064 nm with pulse duration time of 7ns and repetition rate of 5 Hz, using two lenses of f = 5 cm. Measurements were carried out in atmospheric pressure. Laser- induced breakdown spectroscopy (UBS) has been applied to analysis of a wide variety of materials (Ciucci, et aI., 1996 and Corsi, et aI., 2000). The advantages of LIBS over more conventional forms of atomic emission spectroscopy include the facts that real- time analysis can be performed in spatially in dangerous environments. Nowadays it commonly ascertained that the LIBS technique (Laser Induced Breakdown Spectroscopy) is an useful tool for semi-quantitative elemental analysis of surface components in fully unknown samples (Radziemsky, et ai., 1986). By this technique emission spectra are generated as soon as a laser pulse, focused at or near the target surface, initiates the ablation

268 process accompanied by vaporization and atomization of the sample constituents, giving rise the so-called breakdown effect. The laser action has proved to be efficient in originating emission from the elements contained in the sample under study in almost in every case, often requiring only a minor or no sample pretreatment. If the laser energy is coupled to the sample surface with a sufficiently high intensity on a short time scale, the emissions from the plasma formed in the process can give information on the original atomic composition of the sample. A high resolution spectral analysis is required to detect single atomic and ionic emission lines, i.e. the spectral signatures of each element. The lines, once assigned to specific transitions, allow for the qualitative identification of species present in the plasma and their intensities can be used for the quantitative determination of the corresponding elements provided that the complete mechanism of plasma formation and relaxation is understood (Ciucci, et aI., 1996). In the present study, fish fed the minimum requirement of vitamin C (50 mg ascorbic acid/kg diet) and exposed to sublethal concentration of copper (0.35 mg/l) individually and in mixture with cadmium (1.65 mg/I) have higher cupper content (Fig. 1) in gills and liver more than that in kidney and muscles. Moreover, cadmium intensity in gills, liver, kidney and muscles of fish exposed to 1.65 mg Cd/I (Fig. 2) were 10.6, 10.6, 8.8 and 4 times higher than the control group respectively. Furthermore, fish exposed to mixture of cadmium and copper recorded 10, 10, 7 and 3.8. relative to control group in gills, liver, kidney and muscles respectively. On the other hand, fish fed on diet contained high concentration of ascorbic acid (500 mgikg diet), restore cadmium content of the studied organs of the fish to values more or less similar to that of fish of the control group. Cadmium bioaccumulated in gills and liver more than in kidney and muscles (Fig. 2). Moreover, fish fed the minimum requirement of vitamin C (50 mg ascorbic acid/kg diet) and exposed to copper individually (0.35 mg/l) bioaccumulated higher copper with intensity values 7, 8, 4 and 2.4. for gills, liver, kidney and muscles relative to that of control group respectively. However, fish exposed to mixture of cadmium and copper recorded copper intensity values (6, 2.5, 3.2 and 2.1. relative to control group in gills, liver, kidney and muscles) lower than that of fish exposed to copper individually. Iron tissue concentrations and its significant differences are shown in Fig. 3. Data revealed higher iron concentrations in the different studied selected organs of fish fed the minimum requirement of vitamin C (50 mg ascorbic acid/kg diet) and exposed to cadmium (1.65 mg/l) individually or in mixture with copper (0.35 mg/l). It is also clear that, fish fed on diet contained high concentration of ascorbic acid (500 mgikg diet), restore copper, cadmium and iron contents in the studied selected organs to intensity values more or less similar to that of control group.

269 3.2 Gill and muscle electrolytes (Ca, Mg and Na): Exposure of Ciarias gariepinus fed on the rmmmum requirement of vitamin C (50 mg ascorbic acid/kg diet) to 1.65 mg Cd/I individually or in mixture with 0.35 mg Cull induced a strong decrease in muscle and slight decrease in gill calcium (Figs. 4 & 5), magnesium (Figs. 6 & 7) and sodium (Figs. 8 & 9) concentrations than those of the control group. It is also clear that, fish fed on diet contained high concentration of ascorbic acid (500 mg/kg diet), restore the studied electrolytes in gill tissues and slightly muscle electrolytes of fish fed on high vitamin C diet and exposed to the same concentrations of cadmium and copper. Bioaccumulation patterns of metals in fish tissues can be utilized as elective indicators of environmental metal contamination (Sultana and Rao, 1998). Copper exerts a wide range of physiological and histopathological effect on fish (Ortiz, 1997). This metal especially elects gills and liver since they are the main target organs for aquatic pollutants. Cadmium as well as copper are accumulated mainly in the metabolically active tissues of fish such as gill, liver and kidney. Cadmium and copper bioaccumulation in these organs generally has been found in the present study to be lower in fish exposed to the mixture than individual exposure. This record is in agreement with Wu and Hwang (2003) who postulated that copper or cadmium pretreatment increases the protection against cadmium toxicity in tilapia larvae; Oreochromis mossambicus where pretreatment with Cd2+or Cu 2+ enhanced the tolerance of larvae to subsequent Cd 2+ challenge via induction of additional metallothionine. Muscle metal concentration may be regulated and is poor biomonitor of metal accumulation in the immediate ambient environment, thus, Cu accumulation in muscle was homeostatically regulated (Kamunde et ai., 2001), and Cu accumulation in the muscle of rockfish can be used to biomonitor not acute exposure but chronic metal exposure. The higher iron concentrations in the different studied organs of fish fed the minimum requirement of vitamin C (50 mg ascorbic acidlKg diet) and exposed to cadmium (1.65 mg/I) individually or in mixture with capper (0.35 ,g/I), may be attributed to the mobilization of iron from the erythropoietic organs by Cd and/or Cu to the studied selected organs as previously reported by Carbonell et at. (1992). Moreover, copper promotes absorption of iron from the gastrointestinal tract and is involved in the transport of iron from tissues (Goyer, 1989 and Sorensen, 1991). However, the slight decrease in iron concentrations in the studied sleeted organs of fish fed higher vit.C concentrations and exposed to the same concentrations of Cd and/or Cu may be attributed to the improvement in the efficiency of the erythropoietic organs to restore the blood constants to its normal values as well as that of the control group.

270 Bioaccumulation of cadmium and copper in tissues of fish exposed to cadmium (1.65 mg! I) and copper (0.35 mg! l) individually and in mixture provokes iono- regulatory disturbance as revealed by the recorded decrease in gills and muscles calcium, magnesium and sodium. This is in agreement with findings of Baldisserotto et ai., (2004) who reported that water born cadmium exposure decreases the activity of gill ci+- ATPase, which leads to fish hypocalcemia.

3.3 Growth rates: Growth in the most general sense reflects changes in metabolic processes occurring in the organism (Glubokov, 1990) and it can be made to approach an optimum in cultured fish by manipulating temperature, light regimes, water quality and amounts and types of nutrient offered (Weatherley and Gill, 1987). The Nile catfish; Clarias gariepinus fed the minimum requirement of vitamin C (50 mg!kg diet) and exposed to 1.65 mg cadmiumll and 0.35 mg copper/I individually and in mixture for 12 weeks exhibited the lowest growth rate in comparison with the control and other studied groups. This reflects and confirms the toxic action of the studied metals and their interaction. The decrease in body weight gain in fish could be due to the reduction in food consumption and/or the decrease in gross food conversion rate which resulted in inhibition of growth as previously reported by several authors (Waiwood and Beamish, 1978 and ZaghlouJ, 2001). Noel-Lambot et al. (1978) reported that, to uphold the processes vital for survival, fish would have to either increase the production rate of the deactivated proteins or detoxicate the metal. Either way requires additional energy, which would result in weight reduction. However, the highest growth rates recorded in fish fed 500 mg ascorbic acid/kg diet and exposed to the same concentrations of Cd and Cu individually and in mixture reflects the efficacy of vitamin C in inhibiting the toxic effect of the studied metals. One of the most important growth indices of fish is the condition factor which are estimated only for comparative purposes to asses the impact of water quality or other environmental factors on fish performance (Clark and Fraser, 1983). The condition changes may be found to reflect fairly faithfully the changes in body protein and lipid content (Weatherley and Gill, 1983). Fish exposed to cadmium and copper individually and in mixture and fed on diet contained the lowest ascorbic acid concentration (50mg!kg diet), showed lower k factor which may reflect the toxic effect of cadmium and/or copper on body protein and lipid contents and consequently decrease the growth rate (Clark and Fraser, 1983 and Weatherley and Gill, 1983). It is clear from the present study that, high concentration of vitamin C in diet (500 mg/kg diet) restored the condition factor of fish, exposed to Cd and Cu individually and in mixture, to

271

values more or less similar to that of the control group fish, indicating its essential role in inhibiting the toxic effect of the studied heavy metals. 3.4 Serum analysis: The present investigation showed highly significant differences in the studied serum constituents with the highest values in serum glucose, AST, ALT, creatinine and uric acid and lowest values in serum total lipids of fish, fed the minimum requirement of vitamin C in diet and exposed to sublethal concentrations of cadmium and copper individually and in mixture for 12 weeks (Table 2). Moreover, serum constituents of control group fish are in the normal ranges as previously reported by Haggag et al. (1999) and Zaghloul (2001).

The reported hyperglycemia may be due to an enhanced glycogen breakdown in liver (Table 3) that affected by the bioaccumulated cadmium and copper and/or an increase in plasma concentration of catecholarnines and corticosteroids as a stress response of fish subjected to environmental alteration (Mazeaud et al., 1977). Exposure of the studied fish to sublethal concentrations of cadmium and copper individually and in mixture at 50 mg ascorbic acid/kg diet increase the serum total protein to values higher than those of control group. The elevation in serum protein level is consistent with previous results of the effects of heavy metals by Haggag et aI., (1999) and Zaghloul (2001) working on Nile catfish; Clarias gariepinus. The increased serum protein levels indicate an activation of metabolic systems. Moreover, the serum proteins come from degradation of the cellular material in the liver and other organs. The liver is markedly depleted in fish fed the minimum requirement of vitamin C and exposed to Cd orland Cu as indicated by the observed reduction of the hepatosomatic index. Possibly the change of serum protein may be attributed to the histopathological damage reported in the present study as well as to water loss in the serum as reported by Wedemyer and Yasutake (1977) and Zaghloul, (2001). Lipids are an important metabolite for locomotory and reproductory activities of fish. The decrease in the serum total lipids of fish (fed the minimum requirement of vitamin C in diet) exposed to cadmium and copper individually and in mixture may be attributed to the increase in the secretion of catecholamines (Pickering, 1981) and corticosteroids (Mazeaud et al., 1977) as result of pollutant stress. The increased hormonal secretions in blood produces an enhanced metabolic rate which in turn reduces metabolic reserves and affects the physiological status as well as the growth state of fish. Determination of enzymatic activities could be applied to monitor water pollution (Heath, 1995). The elevation in serum AST and ALT activities of fish exposed to cadmium orland copper, at 50 mg ascorbic acid/kg diet, as compared with the control group fish may be attributed to the damage of liver and kidney cells by the action of the accumulated cadmium and/or copper. The same

272 observation was previously reported in case of different fish species exposed to different heavy metals (Zaghloul, 2001 and Elghobashy et at., 2001). Following cell damage, the membranes become permeable and the enzymes are found in the extracellular fluid and serum. So, determination of transaminases, AST, ALT has proven useful in the diagnosis of liver disease in fish (Maita et aI., 1984 and Sandnes et aI., 1988). Valgio and Landriscina (1999) reported that cadmium strongly damages the cellulor membran structure with a concomitat increase in aspartate amino transferase and alanine amino transferase activities in serum. Serum creatinine and uric acid can be used as a rough index of the glomerular filtration rate (Maita et aI., 1984). Low values of creatinine, uric acid and urea have no significant but increasing values indicate the presence of disturbances in the kidney (Maxine and Benjamine, 1985). In the present investigation, fish fed on diet contained 50 mg ascorbic acid/kg diet and exposed to cadmium and/or copper individually and in mixture showed an elevation in serum creatinine and uric acid. This may be attributed to the action of heavy metals on the glomerular filtration rate, which causes pathological changes of the kidney as recorded in the present study. However, increasing the supplementary dietary vitamin C to 500 mg ascorbic acidlkg diet restore the studied serum constituents of fish exposed to the same concentrations of cadmium and/or copper to the normal control values. Fish fed the minimum requirement of vitamin C. (50 mg/kg diet) and exposed to cadmium (1.65) and copper (0.35 mg/l) individually and in mixture exhibited the lowest HSI and higher water content in comparison with the control and other studied groups (Table 3). However, fish fed 500 mg vitamin C/kg diet and exposed to the same concentrations of Cd and Cu individually and in mixture exhibit HIS values and liver water content as those of control group fish. 3.5 Muscle chemical composition (Meat quality): The metabolic pathways of fish can be severely altered by a variety of biological, chemical and physiological factors, which could be assessed throughout several biochemical procedures. The influence of toxicants on muscle chemical composition of fish has been taken into account in evaluating response of the fish against stressors especially heavy metals (Haggag et aI., 1999 and Zaghloul, 2001). In the present laboratory study, fish fed the minimum requirement of vitamin C (50 mg ascorbic acidlkg diet) and exposed to sublethal concentrations of cadmium and/or copper showed the lowest meat quality, where there were a significant increase in muscle water content and ash and a significant decrease in the muscle total protein and total lipids (Table 4). This is in agreement with the work of Haggag et aI., (1999) and Zaghloul (2001) who found a decrease in the

273 muscle total protein and total lipids of the African catfish; Ciarias gariepinus exposed to high concentrations of heavy metals. Depletion of body constituents (muscle total protein and total lipids) results in tissue hydration. This explanation is in agreement with Weatherley and Gill (1987) who reported that, there is an inverse dynamic relationship between protein as well as lipids and water contents in the muscles. The decrease in muscle total protein and total lipids of fish exposed to cadmium orland copper may be attributed to the highly bioaccumulated metals in gills. The bioaccumulated copper and zinc leads to damage in the gill structure, a reduction in the rate of oxygen consumption that causes a sharp reduction in metabolic rate shown by deceleration in fish growth as previously reported by Reader et ai. (1989). The decrease in muscle total protein and total lipids may also be attributed to the decrease in insulin level, detected by the recognized hyperglycemia, which has greater effect on proteogenic and lipogenic pathways (Ablett et ai., 1981). However, increasing the supplementary dietary vitamin C to 500 mglkg diet restore the muscle chemical composition of fish exposed to the same concentrations of cadmium and copper individually and in mixture to the normal quality as those of control group. The efficacy of the naturally occurring chelating agent was confined mainly to the fish fed on the diet contained the higher concentration of ascorbic acid (500 mglkg diet). The present data suggest the value of ascorbic acid for the protecting fish against copper and/or zinc. The most important finding in this study is the observation that ascorbic acid markedly decreased the deposition of cadmium and copper in the different tissues examined. This finding suggest the beneficial use of ascorbic acid in preventing tissue accumulation of both metals. It may be due to ascorbic acid inhibition or interference with copper and/or zinc absorption, due to complex formation of metal with ascorbic acid or one of its metabolites followed by subsequent excretion (Ghazaly, 1994). It is clear from study that, fish fed high concentration of vitamin C (500 mg ascorbic acid/kg diet) and exposed to cadmium and/or copper exhibit more or less similarity to the control group in all of the studied parameters. This could be attributed to the ameliorative effects of ascorbic acid on heavy metals toxicity that may be mediated through its antioxidative actions. Ascorbic acid is known as potential scavenger of reactive oxygen species and it may protect the lipids from detectable peroxidation damage induced by aqueous free radical (Heath, 1995; Sorensen, 1991 and Brake, 1997). Moreover, ascorbic acid (vitamin C) has been shown to enhance also the urinary elimination of metals to reduce hepatic and renal burden of metal (Ghazaly, 1994).

274 A possible explanation of the restoration of the studied histological sections and the other studied parameters, more or less to the normal levels, is that fish fed the vitamin C supplemented diet utilized effectively ascorbic acid as L-ascorbyl-2phosphate. Phosphate moiety protects ascorbic acid from degradation in the intestine or enhances the absorption of ascorbic acid (Lovell and El-Naggar, 1989 and El-Naggar and Lovell, 1991). Nevertheless, ascorbic acid has been found to play important roles in a number of biochemical processes and reactions, such as mixed function oxidation involving the incorporation of oxygen into the substrate (Jaffe, 1984). Finally, one could concluded that, LIBS (laser induced breakdown spectroscopy is very applicable method for biological tissue and environmental prospecting. Moreover, supplementation of vitamin C in catfish diets is necessary as the industry shifts toward more intensified culture and more artificial environments for growing the fish.

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