LASER SCIENCE AND APPLICATIONS PROCEEDINGS OF THE SIXTH INTERNATIONAL CONFERENCE
This page intentionally left blank
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
British Library Cataloguing.in·Publication Data A catalogue record for this book is available from the British Library.
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
This page intentionally left blank
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
This page intentionally left blank
I - Laser Science 1-1. Keynote and Plenary Papers
This page intentionally left blank
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 -
1)
/
/ /
i:
J ~
B
4
0.0 +'o----:or.,----:,r.o----0----:2>-.,----'-/-+--e--+---- 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)
This page intentionally left blank
1-3. Contributed Papers
This page intentionally left blank
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. 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 .
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.
This page intentionally left blank
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
This page intentionally left blank
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
..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
~
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
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 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.
References 1.
J. Bedwell, J. Holton, D. Vaira, J. MacRobert and G. Bown. (1990).Lancet; 335: 289-292.
2.
M. Benaissa, P. Babin, N. Quellard, L. Pezennec, Y. Cenatiempo, and J. Fauchere. J. Infect. Immun. 64 (6), 2331(1996).
3.
M. Cheesbrough. Great Britian at the university press, Cambridge. 58 (1994).
4.
J. Dobson, M. Wilson, and W. Harvey. J. Arch Oral Bio. 37,883 (1992).
5.
Dubois. EID 1(3), 1(1995).
6.
S. L. Gorbach. Gastroenterol. 99, 863(1990).
7.
F. Holstein, E. Roosen-Runge and C. Schirren. Groose-Verlag, Berlin, 14 (1988).
8.
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 .
This page intentionally left blank
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
