Low confinement laser diode structure permits lower modal gain, longer devices and wider stripes. The optimum value of the confinement factor is correlated with the modal attenuation coefficient. For an 1 cm-1 modal attenuation coefficient, the optimum operation is obtained in 12 micrometers stripe and 0.007 confinement factor. In such structures, fundamental lateral mode is preserved at power higher than 1 W.

We report the results of a spectroscopic investigation concerning the time evolution of level populations of atomic hydrogen in the afterglow following a pulsed high-voltage hollow- cathode discharge in noble gases under various discharge conditions (peak voltage across the tube of 4 - 20 kV peak current of 50 - 150 A, halfwidth duration of the current pulse of 30 - 100 ns, repetition rate of 30 Hz, and 1 - 15 torr noble as pressure). A long afterglow duration (more than 100 microsecond(s) ) of the Balmer lines has been observed in helium and neon, accompanied by a population inversion between the n equals 3 and n equals 4, 5, 6 levels of the hydrogen atom. We assume that this behavior of level populations of atomic hydrogen is primarily due to the Penning ionization of hydrogen molecules by collisions with noble gas metastables and by metastable-metastable ionization, followed by selective production of excited atomic hydrogen by dissociative recombination of the molecular hydrogen ion. A simple theoretical model based on these assumptions agrees with the observed shape and size of temporal profiles of hydrogen impurity level populations in helium and neon afterglow.

The performances of a small power He-Se laser tube are reported. A particular geometry allowing the self-heating of Se was used, so that, an optimum quantity of metal vapors occurs in the discharge tube for a selected electric current. The influence of a magnetic field placed in the region of Se reservoir at the optimum discharge current is also described.

Lasers that are equipped with stable optical resonators having large to very large Fresnel numbers and uniform active medium with respect to gain and refractive index, are running multimode, and the highest order transverse mode has the largest mode coefficient. A way to evaluate the global degree of coherence of dominant mode laser beams by using a Gauss- Schell model beam having the same beam quality factor M², is proposed.

This paper deals with the analysis and design of dye-laser resonators, using an optical transfer matrix which describes the behavior of a plane grating in Littrow mounting. The presence of a diffraction grating in a resonator cavity introduces an operation asymmetry in the planes parallel and transverse to the grating's grooves (X and Y operations). Our matrix analysis allows to characterize the resonator stability for both operation planes. Several resonator configurations are discussed and an improved design is proposed.

In the last 10 years intense research has been made with the aim to design and build fiable tunable sources of high power coherent radiation. The most known high power microwave devices as the FELs and FEMs, that work as oscillators or amplifiers of radiation, are discussed in this paper. Some new estimated values by a theoretical and numerical analysis of the interaction, that takes place as a basic mechanism in such a device, of a compact FEL components parameters, are presented comparatively to some recent results in designing and experiment of FEL and FEM devices. The estimated data are for a compact FEL that is intended to work in the domain of far IR-radiation ((lambda) approximately 200 - 230 micrometers ).

We describe a preionization controlled pulsed hollow cathode discharge producing intense electron beams and electromagnetic radiation. As compared with classical pseudospark our discharge configuration allows to minimize the plasma-wall interaction and, consequently, a drastic reduction of the impurity level.

We describe a source of visible (532 nm) radiation for pumping picosecond optical parametric oscillators. Picosecond pulses generated by a passively Q-switched Nd:YAG oscillator are amplified in two amplifier stages and frequency doubled in a KDP crystal cut for type I or type II phase-matching. Trains of pulses of 7 - 11 mJ over-all energy are generated, single pulse energy is 450 - 600 (mu) J and pulsewidth about 40 ps.

Dynamic stable resonators (DSRs) with Nd:YAG lasers which operate up to 1 KW average pump-power are discussed. Some DSR parameters and an ordering criterion are defined. The theory of DSRs has been extended to the Q-switched mode of operation. Two types of resonators able to operate in Q-switched mode are proposed. An experimental verification of the theoretical calculation was made.

In order to determine the stationary modes of active resonators, we have developed a computer model based on the iterative solution of a generalized Kirchhoff-Fresnel integral equation. The model is used for a linear resonator whose parameters (resonator length, diameter and radius of curvature of concave mirror, diameter and output mirror transmission) are known. The computer program was drawn up in the Mathematics language with a modular structure in order to facilitate testing and generalization to the more general case of U-folded resonant cavities.

Structured modifications are produced by interaction of solid state media with high intensity laser beams. The most useful beams for such purposes are generated by CO₂-TE lasers in IR field, and excimer lasers in UV field. The paper describes laser pumping circuits for both lasers with significant temporal decays that occurs between trigger and laser pulses. Also, temporal behavior of above mentioned lasers: pulse duration, delays and jitters, in various operation conditions, i.e., gases mixture, pressure and pumping energy, is made by temporal determination of pulses and delays involved. Finally, synchronization methods, electrical or optical are recommended in relation with necessary conditions of synchronization between beams.

A thermal compensation method (based by using an adaptive optical mirror as the rear mirror of the resonator) was studied in order to improve the quality of laser beam obtained from different super-Gaussian unstable resonators. For a Nd:YAG laser rod the free-running regime was analyzed at 1 Hz, 5 Hz and 10 Hz rates of pumping and different values of pumping energy. Laser pulses with 250 microsecond(s) duration were used. At 5 Hz and 10 Hz rates of pumping the beam quality was maintained at the 0.8 mm mrad value.

A concave-convex stable laser resonator dedicated to a better matching of the waist on large capillaries was developed. Power of 633 nm laser line for different positions of convex mirror for a medium power He-Ne Brewster windows ended, 2 mm ID laser tube was measured. The curves we obtained present an unusual behavior.

Designing of laser diodes needs waveguide parameter optimization and testing. In order to maximize the emitted power of a laser diode an important design parameter is the optical confinement factor (Gamma) of the active region and the reduced confinement factor g equals G/d, where d is the active region thickness. This paper presents a measurement method of the reduced confinement factor by correlating changes in absorption loss with the current density of injected free carriers, for a LPE fabricated double heterostructure single quantum well laser diode with the active region thickness of about 0.1 micrometers . A reduced confinement factor of 8.5 10^-2 micrometers ^-1 and waveguide absorption coefficient of 1.8 cm^-1 of the laser diode are reported.

The paraxial optics of elastic circular plates with clamped or free boundaries, subject either to continuous uniform load, or to a uniformly distributed momentum, is presented. In this way, continuously variable convex to concave mirrors can be obtained. Fused silica and glass plates were considered, and dimensional design formulae are given.

The influence of some factors that affect the diode pumped solid state lasers (DPSSL) efficiency is analyzed. By using simple phenomenological models few simple and efficient criteria fora n optimal design of such DPSSL in an end-pumping configuration were derived. Some numerical results for a Nd:YAG laser are discussed.

This paper describes an analytical and numerical modeling of photon flux dynamics in passively Q-switched Nd:YAG lasers. The types of solutions to the system of nonlinear- coupled equations are related to various possible modes in which such laser systems may operate: before the bleaching of the saturable absorber, the giant pulse mode, the self- oscillating mode.

The variable reflectivity mirror whose behavior was followed in dynamic regime while used in C.W. CO₂ technological laser had the structure: AIR (ZnSe, BaF₂)/GaAs(ZnS)AIR acting as a super-Gaussian mirror. It worked as an output coupler in an U type resonator mounted in a C.W. CO₂ transverse flow laser, the output power characterizing the emitted beam belongs to the interval 800 - 1000 W in the fundamental mode. Following 300 hours of operations, in technological regime and 600 hours of overall operation, the laser beam quality exhibited unmodified characteristics from the point of view of industrial processing of materials.

In order to increase the service life of the passive Q-switch crystals some LiF:F₂ saturable absorber crystals were investigated in different linear resonators: (1) two-mirror, and (2) three-mirror configurations. An active Nd:YAG media laser was pumped with milliseconds pulses (width up to 10 ms) at a repetition rate adjustable over 1 - 10 Hz range. During the experiments the pulse durations, repetition rate of Q-switched pulses in train of pulses, peak powers, beam divergences, pulses energies and average powers were measured. Depending on the characteristics of LiF:F₂ crystals and pumping pulse width, trains of tens to hundreds pulses during a single pumping pulse were obtained. A discussion on the stability of the laser emission and on the service life of the saturable absorber crystals used in these configuration is presented.

This paper presents a comprehensive review of the current methods used in Liquid Phase Photo-Deposition (LPPD). After the introduction, the basic physical principles of LPPD and main technological trends of research are given. Basic requirements for photoreaction systems are described. The critical controlling LPPD parameters are described and details of experimental kinetic investigations are given. We present the theories suggested for LPPD processes and give some application results. The advantages and weaknesses of LPPD are compared to the Gas Phase Photo-Deposition processes.

In this paper we present results on the deposition of titanium nitride and titanium carbide films by pyrolytic laser-induced chemical vapor deposition using a cw TEM₀₀ CO₂ laser beam. TiN lines were deposited onto mild steel substrates while TiC spots were deposited on silica substrates. The microstructure of the surface and of fractured cross-sections of the films were examined by scanning electron microscopy. The topography of the films and the thickness measurements were studied both with diamond-stylus and non-contact laser profilometers. The chemical composition of the TiN films was investigated by electron probe microanalysis. X-ray diffraction was used for phase and structure analyses of the TiC films.

Laser-assisted processes for metal-based thin films deposition are currently using vapor-phase precursors. Either photolytic or thermal, the mechanisms developed during laser-induced interaction between adsorbed precursor and substrate are imposing different trends to the composition and morphology of the growing metallic layer. Various aspects of the dynamics of film growth are discussed, in connection with the deposition of titanium from titanium tetrachloride.

We introduce a new theoretical analysis of the temporal and spatial evolution of surface topography of solids following interference between incident and scattered pulsed laser beams. The essential role played by the nonlinear delayed feedback in the laser radiation-surface system is considered. We show that it finally determines the surface topography evolution from pulse to pulse. In order to complete the analysis, numerical calculations have been conducted under the hypothesis of strong attenuation of laser radiation into the sample and of a limited heat diffusion during the action of a laser pulse. We predict an evolution from very simple to complex (chaotic) structures under multipulse laser irradiation of solid surfaces. This evolution is determined by some key irradiation parameters--initial surface microrelief, incident laser intensity and the number of applied laser pulses. Experiments were performed in order to check-up the main predictions of the theoretical analysis. The system TEA-CO₂ laser radiation ((lambda) equals 10.6 micrometers )--fused silica was chosen as appropriate for performing test experiments. Optical microscopy studies of laser treated zones evidenced special modifications of the surface topography in good accordance with the conclusions following from the theoretical analysis. The theoretical analysis is also in good agreement with some available data from literature, at the same time providing a coherent interpretation of previously unexplained behaviors.

CO₂ laser photosensitized (SF₆) decomposition of diethylsilane proceeds via molecular extrusion of ethene and affords solid Si/C/H materials which possess both Si-C and Si contributions, contain some fluorine from the sensitizing sulphur hexafluoride, and react with ambient atmosphere to incorporate oxygen.

Laser photo induced reactions from gaseous precursors have been applied to the synthesis of nanosized silicon carbonitrides and (gamma) -alumina based powders. Silicon carbonitrides with different structures and chemical compositions have been produced by changing the reactant gases or their relative concentrations. The structural and chemical evolution have been studied by thermal treatments in Ar and N₂ atmosphere. The results confirm the applicability of this powder for industrial applications. Concerning the (gamma) -alumina powder, changes in the reactants concentration ratio have shown to influence both the process yield and the composition of the outcoming powders. Nitrogen or carbon rich (gamma) - alumina powders (Al₃O₃N, Al₂OC) have been synthesized. Some recent and encouraging results on the thermal properties of laser produced silicon carbide are also presented.

Several examples of the application of laser induced fluorescence (LIF) detection to diagnostics of combustion processes are presented. The temperature distribution in a laminar flame can be measured by LIF detection of OH radicals via predissociated states. Two- dimensional density distributions of CH and C₂ are studied by LIF in flame deposition of diamond. It is even possible to apply LIF detection to visualize NO in a running Diesel engine.

From several single arthropods methane and water vapor release is measured with a time resolution of 15 seconds by a liquid nitrogen cooled CO-laser intracavity photoacoustic arrangement. Atmospheric methane is an important component in the process of global warming and ozone depletion. Four taxa of arthropods are thought to be responsible for up to 25% of the total mondial CH₄ release to the atmosphere. The measurement of water vapor release together with CO₂ emission is of importance for understanding the complex breathing pattern of arthropods, in view of evolutional adaptations these animals have undergone to survive terrestrial conditions.

An extensive spectroellipsometric study was performed on titanium dioxide (TiO₂) and TiO₂(Mⁿ⁺) thin films deposited on three different substrates (soda-lime glass, silicon wafers and thick aluminum film/glass) by the sol-gel method. The properties of the resultant films are process dependent. The effects of substrate nature, thermal treatment temperature and doping on the films properties are discussed. The spectroellipsometric results (correlated with X-ray diffraction, Rutherford Backscattering Spectroscopy and X-ray Photoelectron Spectroscopy data) provide precise information on the modification of the optical properties (optical constants, film thickness and interband transitions) of the different types of TiO₂ films with the above mentioned preparation parameters.

Laser radiation interaction with materials is a complex process in which creation of acoustic waves or stress waves is a part of it. As a function of the laser radiation energy and intensity incident on steel target surface ultrasound signals were registered and studied. Thermoelastic, ablation and breakdown mechanisms of generation of acoustic waves were analyzed.

The existence of a large number of vacancies in Cr₂O_3-x was revealed by X- ray absorption spectra and by measurements of the magnetic susceptibility versus temperature. Also, the chemical shift in stoichiometric and non-stoichiometric (alpha) -Cr₂O₃ was determined from the X-ray absorption Cr K edge spectra. The difference in the chemical shifts is produced by the decrease of valence charge of chromium in the non-stoichiometric compound.

CO₂ laser induced infrared multiphoton decomposition of tetravinylsilane affords a variety of gaseous hydrocarbons and Si/C/H films wherein the relative content of Si and C is affected by the temperature of the substrate.

Laser ablation into a microwave induced plasma coupled with atomic emission spectroscopy can be used for microbulk analysis with moderate spatial resolution, dependent on the laser beam parameters and the solid sample. The application of optical fibers as the interface between an echelle polychromator and a gateable optical multichannel detector allows simultaneous measurements in the range of 180 - 800 nm. By this experimental arrangement, results about concentration distribution, element correlation and ablation process itself in metallic (steel, aluminum) and non-conductive (quartz) samples will be presented.

Dimethylamine (DMA) and trimethylamine (TMA) molecules are photolyzed with a TEA- CO₂ laser at 1035 cm^-1 in focussed and unfocussed beams with fluences up to 12 J/cm² and stable products are determined for up to 20 Torr pressure. The formation of stable products like CH₄, C₂H₂, C₂H₄ and probably C₂H₆ proved that the main channel of infrared multiphotonic dissociation (IRMPD) of both molecules consists in scission of CH₃ - N bond. The remaining energized radicals are converted to HCN in TMA IRMPD and HCN and NH₃ in DMA IRMPD. In the last case, secondary reactions between CH₃ radicals and DMA molecules yield to TMA formation. At prolonged irradiation, considerable quantities of TMA are formed which can react with CN and (CH₃)₂N radicals to produce (CH₃)₂N - CH₂ - CN and (CH₃)₂N - CH₂ - N(CH₃)₂ compounds.

A TEA-CO₂ pulsed laser was used to study the infrared multiphoton absorption of protonated and deuterated trichloroethylene (C₂HCl₃; C₂DCl₃). The dependence of the cross section and the average number of photons absorbed per molecule, on laser fluence and laser frequency, for different pressures of gas, was studied.

Emission characteristic of laser produced plasma for two pulse lengths of the laser beam at 10.6 micrometers wavelength was studied. Emission lines in Al and Pb plasma were registered in the visible region their time evolution was analyzed and plasma temperature was estimated. A second maximum in intensity of the emissions lines after the laser pulse extinction was put into evidence for short laser pulses as compared with the smooth decay in time of lines for long laser pulses.

The paper presents the results obtained to the submillimetrical drilling with CO₂ lasers of the 1 - 3 mm rubber plates thick and the distribution of the diameters values of the holes.

The samples were prepared by sinterization at 850 degree(s)C in the solubility range of the investigated system. The energetic structure of the investigated samples and also the chemical shift were determined from the study of the X-ray K Ti edge absorption.

The paper presents three devices for establishing the focal plane position, for keeping the focusing constant and for modulation a CO₂ laser beam in sheets cutting.

In this paper the work on the one-atom-maser or micromaser is reviewed. This maser system is the most fundamental one where a single atom interacts with a single mode of a cavity. With this setup the generation process of non-classical light and other quantum phenomena can be investigated in detail. Furthermore a brief review of the microlaser work will be given where the phenomena of cavity quantum electrodynamics lead to a very low threshold of the laser system.

Experimental and theoretical results are presented for the kinetics of photoinduced absorption in chalcogenide glass fibers. Photoinduced absorption measurements were carried out both at room temperature as well as at liquid nitrogen temperature in a wide range of probing light photon energy hw < E_g. Experimental results are interpreted on the bases of the model with quasicontinuous distribution of localized states in the gap. Both experimental and theoretical results show that subbandgap light can not only reduced the previously induced absorption but can produce an enhancement of photoinduced absorption also. It is shown, that photoinduced absorption data can be used for determining the parameters of localized states distribution. Computer simulation of photoinduced absorption kinetics shows a good correlation with experimental results.

For a tunneling system we consider the coupling to the dissipative environment of the coordinate q, the momentum p and the potential function U(q). In the frame of the quantum theory of open systems we derive a quantum master equation, fundamental constraints and uncertainty relations. We obtain an analytical expression of the tunneling spectrum and show that at thermal equilibrium its shape entirely depends on the barrier characteristics while its amplitude is proportional to the strength of the dissipative coupling.

We used the Riemann Problem Method with a 3 X 3 matrix system to find the single soliton solution for a perturbed nonlinear Schrodinger equation in the most compact form. The considered equation describes bright ultrashort pulse propagation in properly tailored monomode optical fibers. The propagation of different single soliton solutions under the influence of the self-induced Raman effect was illustrated. Unlike the single soliton solution of the standard nonlinear Schrodinger equation we found that one of the our soliton solution can exhibit instability which leads to soliton fission.

Reconfigural volume holograms are important for a wide range of multiple data storage applications, including optical interconnection systems, image processing and neural network models. Several techniques for multiplexing to obtain a large number of stored images which can be recalled independently have been developed. But even the most promising of these multiplexing techniques, angular multiplexing using the selectivity of the Bragg-condition, revealed to be limited primarily because of cross-correlation noise. Other problems are not less severe. In this paper we present an alternative approach implementing a phase coding method of the reference beam. Phase encoding has been discussed for interconnecting vector arrays in thin holograms and to perform array interconnections by correlation of a reference beam with a supplementary phase-coded input beam. In contrast to these investigations, we use a reference beam phase coding method in thick volume holographic media, taking thus full advantage of the selectivity of the Bragg-condition in volume storage media. In our experiments, we stored with pure and deterministic orthogonal phase references 64 images into a photorefractive BaTiO₃-crystal. For this we developed a special phase modulator on the basis of a liquid crystal display. Good reconstruction with low crosstalk could be observed. Compared to other multiplexing techniques as angular multiplexing, our method allows high storage capacity without alignment problems. Moreover, easy, light efficient as well as immediate image retrieval without any time delay is possible. Experimental setup and results will be presented. We will especially discuss in detail advantages and disadvantages of this coding method compared to others.

In this paper, we demonstrate some direct spatial methods for the optical phase reconstruction: the smoothing method (with numerical averaging window) and the band-pass filtering method (with differential gaussian filter) in the (x,y)-domain for image recorded with a sinusoidal reference, the smoothing method for images recorded with a chirped radial symmetric reference and the band-pass filtering (with differential gaussian filter) in the (x,y)-domain for phase-modulated images recorded with an arbitrary reference. Comparisons between the methods in the (x,y)- and Fourier-domains, as well as the evaluation of the range of phase measurement in these methods are done.

Results of the experimental investigations of the nonlinear absorption of microsecond laser pulses in thin amorphous As₂S₃ films are presented. The optical transmission hysteresis at interband excitation of As₂S₃ films in a blue-green spectral region is reported for the first time. A reversible film photodarkening induced in the field of laser pulses was registered. It was suggested that the interband nonlinear light absorption could be explained by taking into account the light interaction with nonequilibrium phonons.

The light self-diffraction in the case of the high modulated phase gratings induced in semiconductor materials is studied by solving numerically the set of the coupled wave equations, which were used previously for gratings produced by linear phenomena. We have extended this formalism to include the case of the absorbing materials and the nonuniformity of the interfering laser beams, which induce the gratings. Finally, we compare this description with our experimental data obtained in the self-diffraction on the phase gratings induced in crystalline silicon wafers by Nd:YAG laser beams. The experimental results are fitting better our theoretical description.

In this paper we present a theory of optical subharmonic generation in a nonlinear Fabry-Perot resonator. Our approach, based on classical electrodynamics, leads to a Mathieu-Hill-type equation. This enables us to describe the generation of optical subharmonic oscillation in terms of a general formalism used to account for parametric phenomena, and to outline the possibility of using a nonlinear Fabry-Perot resonator as a memory device able to store the phase of a signal. The oscillation threshold condition is discussed and the rate of amplitude rise at start-up is evaluated.

The main goal of this work is the implementation of some mathematical notions like attractors, orbits, sensitive dependence and chaos in the study of the multiple reflection of a light beam. We shall analyze some concrete situations of reflection on a circle, on a rectangle and the general case of a conic, all this cases with direct application to the optical resonant cavities of lasers. Using some general results concerning the dynamical systems, we shall point out the conditions that the multiple reflection must satisfy in order to obtain a periodic reflection or chaotic behavior.

The conditions of occurrence of both TE and TM dominant hybrid guided modes in a semi- infinite antiguide array in contact with a positive birefringent uniaxial material are investigated by using the 4 X 4 transfer matrix method. The dispersion relation of hybrid guided modes is exactly calculated. The band structures for the allowed values of the propagation constant and of the anisotropic medium optical axis orientation are illustrated numerically. The upper cutoff thicknesses for various hybrid guided modes are obtained.

A `fast and precise peak finder' was the motive to develop, in a previous paper, a nonlinear, adaptive parameter extraction method when only a few samples of the signal are available; the resulting algorithm has combined precision and speed requirements, surpassing by far the performance of the best linear processing. The present paper analyzes the algorithm behavior in noisy data (the errors rise proportionally to the noise level when this is above the threshold of `systematic error') and describes an improvement which allows one to maintain the precision of the results in the presence of noise an order of magnitude bigger than the threshold.

A JEOL 840 Scanning-Electro-Microscope (SEM) at 20 kV operating potential and with a 3 to 6 nA electron beam intensity has been used to study mural paintings of Stavropoleos Church (18th century, Bucharest, Romania). The SEM offers the opportunity to make point cross- section analysis and to determine the topographic distribution of the chemical elements in every layer. This method was associated with optic-microscopical observations and wet chemistry analysis. Many samples were tested to identify the painting technique, the pigments, the binders and also to point out the particularities of the studied object.

In this paper, we report an all-optical method for the determination of the electro-optic coefficient of the photorefractive crystals. Two laser beams with the wavelength (lambda) equals 632.8 nm interfere in a Bi₁₂TiO₂₀ (BTO) crystal, inducing a phase grating on which they are self-diffracting. The photoinduced space-charge field is anharmonic as a consequence of the high contrast of the incident light fringe pattern imposed by the condition of large diffraction efficiency. Our analytical evaluation of the light intensity in the diffraction orders (in the Raman-Nath regime) and processing of the experimental results led to the determination of the electro-optic coefficient, r. The values of the electro-optic coefficient, obtained for different BTO crystal samples, are in agreement with those reported in literature and obtained by electro-optical methods.

Some signal processing applications require memory modules with very fast access along predefined scan patterns. If this requirement only holds for standard raster scan (image processing) the simple solution of reading in parallel a number of slower memory chips and using a fast parallel to serial converter is enough. This paper focuses on the problems which appear when more different fast scans patterns are required. In this case the mapping of the data in the memory chips is analyzed by using a combinatorial theory setting. We prove that a mapping which allows two different predefined scan patterns does always exist. For more than two different predefined scans our formalism allows one to construct a mapping, if it does exist. The paper presents several examples with 2 and 4 scan patterns.

The main point of the paper is to discuss the control of the correlation for gamma distributed noise images. There is also presented an algorithm of generating uncorrelated noise images of a good statistical quality, with Gaussian, exponential, gamma and Rayleigh distribution.

Equations describing the stimulated Brillouin backscattering have been solved using the method of characteristic equations. More accurate analytical expressions for pump, Stokes wave intensities and width of the backscattered pulse were obtained and a comparison between theoretical and experimental data has been made to explain the pulse compression.

In this paper we present two analog networks that implement an algorithm for motion detection in image sequences. The time consuming stochastic or suboptimal deterministic relaxation algorithms used by the initial Markov Random Field based model are replaced by the energy minimization of the analog network to its state of minimal power dissipation. We describe the elementary cell derived from the model equation and the network architectures. Possible application are motion remote control and motion coding at video rate.

This work presents the technological difficulties and solutions which have been encountered in the construction of a class of devices which use the effect of the interaction between acoustical and optical waves in crystals. An experimental setup for the study of this effect was realized. The connection and matching between the electrical, optical and mechanical components parts were also studied.

By means of two-beam experiments, the transmission properties of highly excited GaSe crystal of different thicknesses (2 micrometers to 1.5 mm) have been investigated in the fundamental absorption and free exciton region. Induced transmission was observed in the whole considered region for lower pump intensities. Results of bistability in an entire ZnTe thin films are present for the first time.

An experimental system for the evaluation of photoacoustic (PA) signal characteristics and noises in a resonant photoacoustic cell excited in its first longitudinal mode by a line tunable and frequency stabilized CO₂ laser is presented. The excitation beam is modulated at a frequency that is coincident with one of the natural resonant acoustic frequencies of the cell. The PA signal detected by four microphones placed in the cell was measured by two methods, namely phase sensitive detection and computer assisted Fourier analysis. Experimental measurements in air, N₂, SF₆ and C₂H₄ at various pressures (