Laser Science and Applications

The following sections are included:

• FOREWORD

• PREFACE

• CONTENTS

A method to obtain near trans form-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.

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.

It is now a fact that focusing an intense ultra short laser pulse onto a gas jet or thin targets, generates energetic collimated electrons or ions forming ultra short beams of energies > 100 MeV. The different mechanisms to explain such laser accelerated electrons or ions will be discussed. Data obtained by recent experiments will be presented. We report the experiment planed to study laser accelerated ions and/or particles using picosecond and femtosecond high energy laser pulses focused to achieve intensities >10¹⁸ watts/cm². 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.

Energy levels, oscillator strengths, and transition probabilities for the 1s² 2s² 2p⁶, 2p⁵31 (1 = 0,1,2), 2p⁵41 (1 = 0,1,2,3) states in S VII, Cl VIII, and Ar IX are calculated using COWAN code. The Correlation and relativistic 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, Cl VIII, and Ar IX ions over a wide range of electron density (from 10⁺¹⁶ to 10⁺²⁴ cm^-3) at various electron plasma temperatures. The gain coefficients are determined and plotted against the electron densities.

Level structure, oscillator strengths, and transition probabilities are evaluated for 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰, 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁹ 41 (1=0,1,2,3,4), 1s² 2s² 2p⁶ 3s² 3p⁵ 3d¹⁰ 41 (1=0,1,2,3,4), and 1s² 2s² 2p⁶ 3s¹ 3p⁶ 3d^l0 41 (1=0,1,2,3,4) states in W⁴⁶⁺. The calculations are carried out using COWAN code and are compared with other results in the literature. A good agreement is found.

The results are used in the determination of the reduced population for 14 fine structure levels in W⁴⁶⁺ ion over a wide range of electron density (from 10⁺¹⁷ to 10⁺²⁵ cm^-3) and at various electron plasma temperatures.

For those transitions with positive population inversion factor, the gain coefficients are determined and plotted against the electron density.

We investigated Low-Temperature Photoluminescence (PL) spectra of ZnSe_xTe_1-x were grown from the melt where 0≤x≤0.202, the spectra of ZnSe_xTe_1-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 ZnSe_xTe_1-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 ZnSe_xTe_1-x ternary alloys exhibit one mode behavior.

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 (BGS). 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 BGS 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 BGS 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.

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 ±1.7×10^-5, ±9.5×10^-6 and ±7.25×10^-5 respectively.

Some calculations of the electrical properties are carried out such as the optical permittivity dielectric susceptibility and specific refractivity from the determination of the refractive 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.

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

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

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

Conserving the built heritage, including architectural and urban monumental sites, has its various methods and tools for restoration. Restoration can be considered as a tool used by archaeologists for preserving monuments. Then, engineers have to play their role in developing different methods and techniques for conservation, and rehabilitation if needed, of the architectural and urban heritages. Accordingly, technological advancements may result in providing a futuristic vision of the project, without conducting experiments on the monument itself exposing it or its elements to distortion or deterioration.

This research aims to show up the role and significance of technology and new tools in the conservation of historical built heritage, which may be considered via:

• Addressing the concept of conservation and restoration and its evolution over time.

• Revealing new methods and techniques for conservation.

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

• Documentation of the built heritage.

• Computers programs capabilities that can assist in conservation and rehabilitation.

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

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

In the last few years digital optical design had major attention in research fields. Many researches were published in the fields of optical materials, instruments, circuit design and devices. This is considered to be the most multidisciplinary field and requires for its success collaborative efforts of many disciplines, ranging from device and optical engineers to computer architects, chemists, material scientists, and optical physicists. In this study we will introduce a survey of the latest papers in the field of optical materials and its properties for light; this paper is organized in three major sections, optical glasses, compound materials and nonlinear absorption (multi photon absorption) and up-conversion.

Designing digital circuits has a high priority in research field in the present time; it shall also still the main concern of many researchers in the future. Many studies in this field are in progress some are published and other still confidential. This paper proposes a design for elementary digital circuits; NOT, OR, AND; using light as direct inputs. These circuits then process these optical inputs to produce optical outputs without changing the light rays to any other type of energy or wave. The proposed design depends on mirrors, lenses and properties of light to introduce new digital circuits design using infrared rays as its inputs.

Bacterial resistance against antibiotics is an increasing problem in medicine. This stimulates study of other bactericidal regimens, one of which is photodynamic therapy (PDT), which involves the killing of bacterial species by low power laser light (LLL) in the presence of photosensitizing agent. It has already been shown that, various gram- negative and gram-positive bacteria can be killed by photodynamic therapy in vitro, using exogenous sensitizers. The mechanisms of laser action on bacteria are not adequately understood. Here, PDT on H. pylori, as an example of gram negative bacteria was studied. The ultra structure changes of the organism after PDT were examined under electron microscope. Neither Irradiation with laser without sensitizer nor sensitizing without laser has any lethal effect on bacterial cells. However, the successful lethal photosensitization was achieved by applying certain laser dose with the corresponding concentration of the photosensitizer. On the other hand, PDT has no significant effect on the genomic DNA of the cells.

Photodynamic therapy (PDT) is a novel treatment modality of cancer and non-cancerous 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 flowcytometer. Mode of cell death was detected by flowcytometer 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 1 hour (p<0.001) or 24 hours (p<0.001) post incubation. There was a significantly lower viability percentage of normal cells incubated with MB and photoirradiated with diode laser compared to normal cells treated with MB alone for either measured after 1 hour (p<0.001) or 24 hours (p<0.001) post incubation. The decrease in viability was more enhanced with increasing the incubation time. For normal cells incubated with photopherin either for ½ an hour or 1 hour, there was a weak cytotoxic effect compared to the effect on untreated cells. There was a significant decrease in viability percentage of cells incubated with photopherin either for ½ an hour or 1 hour and photoirradiated with He:Ne laser compared to normal untreated cells. The decrease in the cell viability percentage was significantly lower with the use of PDT (photopherin and He:Ne laser ) compared to either photopherin alone or He:Ne laser alone. The decrease in viability was more enhanced with increasing the incubation time. The same effects reported on normal cells were detected on leukemic cells on comparing different methods used. However a more pronounced decrease in cell viability was detected. The most efficient ways of decreasing viability of leukemic cells with much less effect on normal cells was the use of PDT of cell incubation with MB for 1 hour then photoirradiation with diode laser and PDT of cell incubation with photopherin for 1 hour then photoirradiation with He:Ne laser. Flowcytometer (FCM) was more sensitivite than the light microscope in detecting the decrease in cell viability, it also helped in determining the mode of cell death weather apoptosis, necrosis or combined apoptosis and necrosis. Apoptotic cell percentage was higher in PDT of MB and Diode laser or photopherin and He:Ne laser, treated ALL cells compared to untreated ALL cells after 1 hour but was significantly lower after 24 hours post irradiation. A significant increase in necrotic, combined necrotic and apoptotic cell percentages either measured 1 hour or 24 hours post PDT, compared to untreated ALL cells and PDT treated normal cells. Electron microscope helped in detecting early cellular apoptotic changes occurring in response to different therapeutic modalities used in this study. In conclusion, PDT proved to be an effective clinical modality in decreasing the number of leukemic cells when irradiated in vitro with appropriate laser and photosensitizer system. Both PDT systems used in this study were efficient in inducing cell death of leukemic cells compared to untreated leukemic cells. However, photopherin PDT system was more efficient in decreasing the cell viability. A significant decrease in viability percentage was detected when studying the effect of PDT on leukemic cells compared to that on normal cells. This suggests that PDT when applied clinically will selectively differentiate between leukemic cells and normal cells, offering a successful component in ALL therapy.

Photodynamic Therapy (PDT) is a successful new therapy for malignant and non-malignant diseases. It is based on the activation of a photosensitizing dye by visible light in the target tissue, followed by production of cytotoxic substances. The article gives a short overview on the field of PDT with main focus on molecular mechanisms and apoptosis. It includes photodynamic principles, clinical application and procedures, biological effects, molecular mechanisms of damage processing and apoptosis.

Two purified diets were formulated and fed to seven groups of the Nile catfish; Clarias gariepinus for 12 weeks. The formulated diets contained 50 or 500 mg/kg diet of an ascorbic acid equivalent, supplied by L-ascorbyl-2-monophosphate (Mg salt).

Laser induced breakdown spectroscopy (LIDS) technique has been used to characterize the bioaccumulation of cadmium, copper and iron in some selected organs (Gills, liver, kidney and muscles) and disturbance in the distribution of sodium, calcium and magnesium in gills and muscles of fish fed the minimum requirement of vitamin C (50 mg/kg diet) and exposed to cadmium (0.165 mg/l) and copper (0.35 mg/l) individually or in combination. Heavy metals bioaccumulation affect histological structure of gills, liver and kidney and consequently, fish exhibited the lowest growth rate and meat quality with a progressive fall in RBCs count, Hb content and haematocrite value. These effects were concomitant with significant increase in the WBCs count, serum glucose, total protein, AST, ALT, creatinine and uric acid. On the contrary, serum total lipids and liver glycogen revealed a significant decrease.

However, fish fed 500 mg vitamin C/kg diet and exposed to the same concentrations of cadmium and copper either individually or in mixture showed an improvement in the growth rate and meat quality and a tendency to exhibit close to the control values for most of the other studied physiological, biochemical and histopathological investigations.

The following sections are included:

• AUTHOR INDEX