Laser induced plasmas remain after many years of research, mainly for thermonuclear fusion, a field of investigation with new applications, such as X-ray lithography, X-ray microscopy, multicharged ions spectroscopy, material processing, laser induced recombina-tion plasma a.s.o.

The effect of chromium doping on the radiation stability of rare earth doped garnet crystals is investigated. An increase in radiation stability of rare-earth scandium gallium or aluminium garnets at high chromium concentrations is found. Thermoluminescence and absorption data are used to explain the nature of this effect.

Among non-radiative processes which may be encountered in laser materials such as : self-quenching, up-conversion, excited states absorption, multiphonon non-radiative transitions, the last ones may play a particularly important role in vibronic laser materials because the tuning range is directly connected with electron-phonon coupling strength and phonon energies for vibronic radiative transitions. In this lecture we shall discuss two aspects. First we shall try to answer the question: to what extent could the large tuning range also be connected with large coupling strength and phonon energies for non radiative transitions? In such a case, one would have to trade tuning range for quantum efficiency. Which would be a limitation of a basically intrinsic nature in such laser materials. Examples taken from spectroscopic studies and lifetime measurements of Ni²+ and Co²+ doped fluorides and oxydes hosts show that effective phonon modes coupled to radiative and non-radiative transitions are different. In particular in the case of the MgF₂:Ni²+ laser, the mode mediating the tuning range appears to be at a lower energy and with a stronger coupring than the one mediating quantum efficiency trough multiphonon non-radiative decay. A second aspect that shall be discussed is the concentration enhanced electron-phonon coupling that appears to occur in such materials and which could constitute a self-quenching process of a novel type.

Lasers in the triplet spectroscopic series of molecular hydrogen and molecular deuterium were discovered in the mid-infrared band. These are at 3.84, 3.77 and 3.71 microns in ydrogen and at 4.71, 4.60 and 4.52 microns in deuterium. These lasers operate in the a3 - On system in both molecules but the assignment is not so certain in deuterium §s it is in hydrogen because of the lack of sufficient spectroscopic coefficients for the c3 state. The laser data have been used to identify heretofore unidentified infrared lines in hydrogen and deuterium. Future work is planned to include extension of the laser data base for the AV = -1 transitions and an attempt to produce the AV = 0 lasers.

The development of wide range continuously tuhable lasers is an important problem of quantum electronics. A great achievement in this field has been made by color center lasers. This paper is devoted to the development of powerful widely tunable solid state laser systems. Our earlier results in obtaining tunable lasing in the near IR region, in LiF crystals with F; and F. color centers finally resulted in the development of the pulse-pe-riodic computer scanned tunable color center laser "MALSAN-201". The device has two independent optical channels working simultaneously (Fig 1).

Results showing the nonlinear properties of lyotropic liquid crystals and semiconductor doped glass interfaces in c.w. operation are presented and discussed.

Some recent results in the field of femotosecond laser pulse generation are reviewed, including the generation of 6 fsec duration pulses and its applications to time resolved spectroscopic studies in condensed matter. In this paper we review some recent results in the field of femtosecond duration laser pulse generation, together with some applications to the study of dynamic processes in ma-terials. a) Generation of 6 femtosecond laser pulses Pulses as short as 6 femtoseconds can be generated today through the use of a pulse compression scheme that is able to compensate the phase distortions of the propagating pulses up to third order 1 This system works with pulses generated in a colliding pulse mode locked dye laser 2 emmiting 50 fsec pulses which are amplified to an energy of a few microjoules in a copper vapor laser pumped multipass amplifier 3 . A fraction of the amplified pulses is coupled into a small length (9 mm) of monomode optical fiber which has a core diameter of 4 micrometers. Due to the process of self phase modulation the spectral width of the pulse emerging from the fiber is much larger than that of the input pulse. This pulse can then be compressed through the use of a suitable dispersive delay line which corrects the phase distortions accumulated by the pulse upon propagation in the fiber. This delay line is made up of a combination of a pair of diffraction gratings and a pair of prisms, in such a way that by a careful adjustment of the prism and grating separation it is possible to correct the phase distortions in the pulse up to third order.

Large scale Nd:YAG crystals grown by temperature gradient technique (TGT) are discribed. The formation and development of defects in the crystals have been systematically studied.

Laser excited and time resolved fluorescence spectra of low valence transition-metal ions (Cu⁺, Ti³⁺, Cr³⁺) in various kinds of inorganic glasses (phosphate, fluorophosphate and fluoride) have been studied at low and room temperatures. Dynamic lattice model and site structure of activated ions are discussed.

We analyze the role of self-focusing in the interaction of a powerful laser beam with an underdense plasma and the main instabilities whose growth is enhanced by self-focusing. These latter are in turn showed to be useful diagnostics for the nonlinear process, which is expected to produce local heating and density gradients. We report some results from two experiments performed with laser sparks and preformed plasmas from solid targets.

A rewiew is provided of the state of the art and perspectives of high average power lasers for materials processing. An analysis, of the present and projected performances and of the present and future technological requirements, is performed, with special attention to the solid state lasers (Nd-YAG or Glass) and to the gas lasers (CO₂ and Excimers) of industrial interest. Excitation of the active medium and heat removal techniques, time and space control of the emission, and beam transport problems are discussed and compared for the various types of lasers. The expected improvements in the excitation techniques of the active media, and in the resonators configuration are also outlined. New laser candidates for materials processing are evaluated and compared in perspective with the present ones. A brief survey of lasers used in micro processing, with special attention to the applications in microelectronics, is also presented.

The results of experimental and theoretical analysis concerning the properties of the active medium of a high power CO₂ laser are presented in the paper. In order to optimize the characteristics of the laser performance some modifications of the excitation system are proposed.

Many practical devices of technical interest rely for their operation on the coherent interaction between harmonic electromagnetic fields and ensembles of charged particles, constrained to move in orbits or trajectories by electric or magnetic fields. These have in many cases been studied by different communities of physicists and engineers, and different points of view have emerged. At one extreme, a purely quantum mechanical optical approach is appropriate, at the other, classical engineering concepts developed originally for lumped circuits may be more suitable. Some relatively recent developments, such as the gyrotron and free electron laser have features in common with lasers, microwave tubes, and particle accelerators. Some of these devices will be examined in an informal way from several different view points, with emphasis on a physical rather than mathematical description. Similarities and essential differences will be noted.

The effect of the concentration luminescence quenching of the ⁴F _3/2, level of Nd³⁺ in YAG on the relative efficiency is presented. Based on the analysis of the decay curves in terms of the energy transfer theory, an analytical expression for the relative luminescence efficiency is obtained. In the low concentration range (up to q,1.5 at % Nd³⁺), the efficiency linearly decreases when Nd³⁺ concentration increases. It is also stressed that pairs quenching contribute about 20 % to the nonradiative energy transfer losses. Quantum efficiency of luminescence is an important parameter for the characterization of laser active media; its lowering is due to either multiphonon relaxation or energy transfer processes. The multiphonon non-radiative probability depends on the energy gap between levels, on the phonon energy and temperature; usually at low activator doping it is practically independent on concentration. On the other hand, energy transfer losses show a marked dependence on activator concentration, a fact that severely limits the range of useful con-centration of active centers in some laser crystals. In the YAG:Nd case the minimum energy gap between the Stark components of the 4F,I.) and the next lower level ⁴F_15/2 is of about 4700 cm-1. Since in YAG tree phonons most effdbtively coupled to the Rare pi.th ions have an energy of 1, 700 cm-1, the probability for multiphonon relaxation from the 'F3/, level, even at room temperature, is very low and therefore for low Nd ³⁺ concentrations quantum efficiency is expected to be close to 1.

In recent years second-harmonic generation (SHG) has gained popularity as a surface analytical technique. Its intrinsic surface sensitivity can make it useful for studying thin films, or even monolayers. In particular, numerous works have appeared where SHG was used to study monolayer or multilayer films of organic molecules deposited by the Langmuir-Blodgett (LB) deposition technique.Often the interest has been in deriving information about molecular hyperpolarizibilities, or orientational properties of single molecules or parts of molecules. In this work we show that structural information is also available at the supramolecular level.

Optical absorption and pulsed damage threshold at 10.6 μm are reported on samples taken from the same large ultratransparent KC1 single crystal, grown by injecting the reactive atmosphere (IRA) technique. The radial optical homogeneity of the crystal is demonstrated.

The emission of a transversely pumped dye laser using the rate equation approximation is described considering both the laser and the amplified spontaneous emission (A.S.E.) modes, when a pulsed pumping laser is used. The computed results are in good agreement with the experimental data when the real spatial distribution of pumping energy is considered. A N₂-laser pumped tunable dye laser useful for low concentrations measurements of complex mole-cules in solutions is described.

Based on the theoretical models presented in the references in this paper we obtained the expressions of the third and fifth harmonic fields and of the multiphoton ionisation density current in nonlinear media, using the Maxwell-Bloch Equations. The developed formalism allows the study of the competition between multiphoton ionization and third and fifth harmonics generation by computer simulation.

A new non Markovian, correlated jump model for phase fluctuations of an electromagnetic field is introduced'. The phase diffusion, generalized telegraph, Burshtein and Brownian-motion-like models are all obtained from this model in the proper limits. The spectrum and correlation functions of the stochastic field are predicted, and detailed lineshapes of the Mollow triplet of resonance fluorescence are given and shown to depend on the field intensity, a purely non Markovian effect. Two different experimental procedures are proposed for the determination of the stochastic parameters of a laser field.

In the framework of a general theory of open quantum systems, we obtain a quantum master equation for the two-level atom interacting with a single mode of the electromagnetic field. On this basis, we obtain new optical equations. In comparison with the conventional Bloch-Feynman optical equations which contain three phenomenological parameters, the new equations contain nine phenomenological parameters. New physical effects , due to the opening of the system, are predicted: 1) a resonance frequency shift, 2) an asymmetry of the spectral line, 3) a modification of the dependence of the absorbtion coefficient and of the nonlinear dephasing on the atomic detuning, and 4) an additional nonlinear dependence of the absorbtion coefficient on the electric field. For a rather small atom density when the fourth effect can be neglected,we found an analytical expression of the transmittivity characteristic of an optical bistable Fabry-Perot resonator and found a good agreement with the experiment.

Five series of laser dyes with different chemical structure were synthesized and their lasing properties were studied experimentally. The pumped light source was a pulsed N₂ laser. Effect of the different substituents on lasing and spectral characteristics was discussed.

An experimental study of the influence of the radiation in the region 300 nm on the inverse population of the iodine atoms in an iodine laser is presented. The influence was studied in a free running regime and in the regime of the amplifier. The presented calculations show very good agreement for helium poor mixtures. In the frce running regime the additional illumination leads to an enhancement of the generated energy by approximately 10 %.

Instabilities manifest in the general study of optical bistability are considered taking into account quantum statistical aspects. A numerical analysis of the solution of the Fokker-Planck equation for P(x) = I dcp PG(x,(p) is presented, where PG(x,(p) is the Glauber distribution function.

The aim of this work is to report a new method to achieve a light weight, compact, high power CO₂ laser which can be used in industrial applications. It is shown that a metallic cylinder with a relative small diameter (0.6 m) can assure the same flow velocity and cooling of the gas mixture like in previous systems using aerodynamic wind tunnels and special heat exchangers. The construction and operation of a gas transport CO₂ laser with cylindrical geometry and two parallel electrical discharges are presented.

The energy transfer processes in YAG:Er and YAG:Nd are discussed in connection with their effect on the kinetics of population of the levels involved in the laser emission. In YAG:Er the energy transfer processes de-excite the terminal laser level ⁴I3_/2 and repump the initial laser level T 4-11p thus assuring a high efficiency of the three-micron emission at the Room Temperature in high concentrated crystals. A study of the departures from the exponential decay of luminescence of the pump level in in YAG:Er and of the metastable level ⁴F_3/2 in YAG:Nd at activator concentrations up to 1.5 % show that these levels can transfer the excitation by cross-relaxation with identical activator ions and this transfer is of direct (static) donor-acceptor type. For YAG:Nd these processes limit severely the useful activator concentration.

The talk reviews essential physical processes, experimental and theoretical results, concepts and trends of light pulse compression based on chirp production and compensation. In particular the pulse propagation in optical fibers is dealt with, where for positive group velocity dispersion the intensity dependent refraction index impose a linear frequency chirp on an optical pulse, which can be subsequently compressed by a dispersive delay line such as a grating pair. In particular the compression of high-energy light pulses is treated. Negative group velocity dispersion leads to soliton propagation phenomena. The influence of stimulated Raman scattering on pulse propagation in optical fibers is considered.

A Nd-Phosphate glass oscillator is presented emitting laser radiation of 0.5 MW power with 5 % stability at a repetition rate of 0.8 pps. It allows an optimization of the spectral parameters of the emitted radiation in order to achieve maximum amplification in solid state High Power Laser Arrangements.

In this paper, we discuss various experimental advantages which are gained by using samples which have special dimensions and/or geometries. We limit our discussion here to the cylindrical geometry appropriate for optical fibers which are employed for various optoelectronic applications. We present results of laser spectroscopic studies of nominally pure and activated single crystal and glass fibers to illustrate some of these advantages. For example, we have succeeded for the first time in obtaining the dependence of the ruby R-lines and of the Raman spectra of sapphire on tensile stress. We further discuss a novel laser spectroscopic method, Dilution Narrowed Laser Spectroscopy or DNLS; we demonstrate this form of spectroscopy on single mode glass fibers activated with rare earth ions and consider the possibilities inherent in this technique.

New results on excimer laser application for fine surface structurization are presented. There are considered peculiarities of the UV-photon induced processes of:(i) chemical deposition of carbon and silicon carbide films from CC1₄ and CH₃SiC1₃vapour precursors onto dielectric substrates,(ii) chemical etching of c-Si in CC1₄ vapour environment, and (iii) microstructures production by decomposition of organo-metallic (metal resinate) films. The fundamental role of superposition of thermal and photo-stimulated processes is also discussed.

A method of laser cutting of glass tubing through melting is proposed. The experimental and theoretical results from the investigation of the laser cutting are presented. The theoretical model developed gives a good physical comprehension of the method.

The particles adsorbed on the solid-state surface considerably affect tne processes occurring in the solid-state and related medium. Thus, the induced change of the adsorption properties of one of the components of a gas mixture or solution can lead to a disturbance of phase equilibrium, whereas the presence of metal molecules and atoms on the solid state alters its electrophysical properties. So, an interesting problem in the physics of surface is a search for new wavy of affecting the composition and amount of the adsorbed particles. The most promising methods from this point of view are the contactless methods say, photosorption, arising under laser irradiation of interface boundary. The excited resonance molecules on the surface are either ionized and directed by the external electric field or, while remaining in molecular state, they receive an energy which is sufficient for overcoming the adsorption potential.

Microstructural studies of silicon dioxide films grown by laser and by traditional means using infrared spectrometry are described. Broad similarities and intriguing thickness dependences are discussed. A new technique of Direct Growth Lithography (DGL) is reported, whereby oxide patterns are selectively and directly grown over significant regions of a silicon wafer, with spatial features extending over a 3mm square area with linewidths down to around one micron.

Quantitative difference between Raman and resonant Raman scattering spectra of thin ZnSe layers on GaAs substrates is presented. The dynamics of changing of Raman scattering properties while shortenning the exciting light wavelength for ZnSe/GaAs heterojunction is given. The difference in polarization spectra is demonstrated.

The effects of an external electric field on the luminescence and absorbtion properties of asymmetric coupled quantum wells (ACQW) structures consisting of two quantum wells of different width and depth are investigated. Experimental results are presented for two GaAs/AlGaAs coupled well systems, demonstrating the large shift and the sharp turnoff of the wavefunction overlap. We have observed the transition from type I (spatially direct) to type II (spatially indirect) in GaAs/AlGaAs ACQW. The transition is manifested as a strong electric field-induced quenching of the photoluminescence which correlates well with the results of a single particle calculation of the electron-hole overlap. By properly designing the coupled well structure, photoluminescence quenching (90% - 10%) is observed for a change in bias field of only 5 kV/cm. Owing to the large level repulsion, a Stark shift of 5 meV is observed when the bias field is switched by only 18 kV/cm.

Laser-induced chemical etching of (100) Si in C1₂ atmosphere has been investigatEd using a combined laser-beam irradiation scheme. 308 nm XeC1 excimer laser radiation at parallel incidence has been used to exclusively generate Cl atoms in the gas phase abovE the Si surface. Additionally, 647.1 nm Kr+ laser radiation at perpendicular incidence has been used to exclusively generate photocarriers within the Si surface. The Cl atom concertration was determined - independently - from both the observed chemiluminescence following the Cl-Cl atom recombination, and from numerical calculations. The etch rate W observed or the Si surface was found to be directly proportional to the Cl atom concentration in,tpe gas phase, and it increases sublinearly with the Kr⁺ laser power P according to W ≈ P^0.7. The microscopic mechanisms of photo-enhanced etching are discussed.

The most relevant results obtained in the field of the synthesis of metal suicides with pulsed lasers in the nanosecond regime are reviewed. Particular emphasis is given to the results obtained in our laboratories. Formation of stable and metastable compounds, their structure and the surface morphology of the irradiated materials are discussed. The reaction kinetics is investigated through a comparison of the experimental results with the temperatures of the irradiated samples, calculated by solving the heat diffusion equation.

In the paper some of the specific features of the pulsed laser-plasma deposition method are discussed, which are important for the stoichiometric deposition of compound materials of determined thickness and structure. On the bases of some experimental investigations the optimum conditions for synthesis of some polycomponent materials are characterized.

The investigation of laser interaction with solid surfaces and of the resulting mechanism of surface modification are of technical interest to optimize technological processes, and they are also of fundamental scientific importance. Most instructive indormation is available with the ail of the in-situ techniques. For instance, measuring of the photon emission of the irradiated surface ane the plasma torch (if it is produced) simultaneously to laser action, makes it possible to gain a global characterization of the laser-solid interaction. In order to obtain additional information about surface and structure modifications in microscopic detail , a laser and scanning electron microscope were combined in to a tandem equipment (LASEM). Inside this eqiipment the microscopic observation is carried out directly at the laser irradiated area without any displacement of the sample. In this way, the stepwise development of surface modification during multipulse irradiation is visible in microscopic details and much more reliable information about the surface modification process is obtainable in comparison to an external laser irradiation. Such kind of equipments were realized simultaneously and independently in the Institut of General Physics (Moscow) and the Central Institute of Solid State Physics and Material Research (Dresden) using a CO₂ and a LTd-glass-laser, respectively. In the following the advantages and possibilities of a LASEM shall be demonstrated by some selected investigations of WC-CO hardmeta. The results were obtained in collaboration by both groups with the aid of the pulsed CO₂-laser. The TEA CO₂ laser was transmitted through a ZnSe-window into the sample chamber of the SEM and focused ofAo tfte sample surface. It was operated in TEM - oo mode with a repetition rate of about 1 pulse per second. A peak power density of about 160 MW/cm² was achieved in front of the sample surface.

The questions which are discussed in this lecture refer to one of sections of laser-solid interactions, namely: to formation of different dissipative structures on the surface of metals and semiconductors when they are irradiated by intensive laser light in chemically active media (f.e.air). Some particular examples of the development at different spatial and time instabilities, periodic and stochastic structures, auto-wave processes are present-ed using testing materials vanadium metal and semiconducting V₂0₅ single crystals and light sources: cw and pulsed CO₂ and YAG lasers.

New chemical vapor deposition (CVD) processes controlled by light irradiation have been studied and applied to device processing. The physical interaction between the photons of the incident. light and the gas-semi-conductor system are either photolytic or pyrolytic. Lamps or lasers can be used in both processes respectively for large area thin film deposition or thin film direct writing. The control of the reaction by the light implies that the thermal exposure of the substrate is minimized. Light assisted CVD is thus a cold process suitable for brittle materials such as III-V compound semiconductors and also suitable for in-situ multi-processing. Exemples of dielectric layer formation will be treated with emphasis on electronics properties as a warrant of material and interface quality. In situ multiprocessing is also illustrated here.

Device quality PbS photoconducting films were obtained by laser plasma vapour deposition on special glass substrates at room temperature and their structure was investigated by X-ray diffraction. High Tc superconducting films of composition Dy_0.2Y_0.8Ba₂Cu₃O~₇ and YBa₂Cu₃O~₇ were deposited on sapphire substrate. It was shown for laser deposited YBa₂Cu₃O~₇ that a buffer layer of the same composition predeposited by rf sputtering allows for getting high quality superconducting films.

The up-to-date technology of semiconductor devices employs a number of doping procedures for semiconductor materials including epitaxy from the gaseous and liquid phases, diffusion, variation of the crystal growth conditions by a particular program1. These pro-cedures are time-consuming and complicated, since they involve a series of accurate and laborious processes. Besides, the doped layers thus obtained feature a large thickness ,and p-n junctions - a large depth.

The laser applications in nuclear particle detection are discussed. The principle and construction of the laser illuminated streamer chamber with triggered heat centres, a new vertex detector proposed and bui1d-up at JIWR Dubna, are presented.

We summarize the work conducted by our group over the past seven years on the development of coherent surface structures on solid surfaces during illumination by single, intense laser beams. We show how interference effects lead to the formation of structures on many different types of solids with a periodicity which is related to the wavelength of light and angle of incidence of the beam. The spatial spectrum of such structures and their detailed morphology, however, can depend on beam polarization and pulse width. The latter parameter, in particular, can grossly alter the nature of the feedback which allows these structures to develop and grow from a randomly rough surface. We demonstrate these differences with structures generated by nanosecond pulses and continuous beams on silicon and germanium. Most recently, a new class of periodic structure has been generated on silicon and germanium surfaces by picosecond laser pulses at repetition rates of 80 MHz. These structures have a periodicity nearly an order of magnitude smaller than the wave-length of light and are linked to the generation of surface acoustic waves by strongly absorbed light. In all cases we offer an overview of the key experimental observations and discuss the salient theoretical ideas without attempting to be detailed or rigorous.

An analysis of the time evolution of the growth of W spots deposited by hydrogen reduction of WF6 under 647.1 nm Kr ion laser irradiation is presented. From measured lateral growth rates of the spots and model calculations for the temperature distributions in the deposit/substrate system the chemical kinetics that controls the deposition process is determined. The apparent chemical activation energies derived for substrates of fused quartz covered either with 70 nm of sputtered W or with 120 nm of amorphous Si (a-Si) are 30 kcal/mol and 40 kcal/mol, respectively.

A new method for the determination of the electro-optic constant is proposed and de-monstrated for polycarbonate films doped with 4-diethylamino-4'-nitrostilbene. Third-order nonlinear susceptibility x(³)(-w; w, 0,0) of the film was determined between 00 and 800 nm at room temperature by using this method. X(3)(-wi5,0, 0) is (64-4i)x10^-12 esu or quadratic electro-optic constant is (-1-0.7i)x10-20 m2/1T2 at 597 nrn,

The periodic structures generated on metallic surfaces under high intensity laser irradiation are discussed as dissipative structures by analogy with Benard patterns.

An analytical expression is inferred for the field amplitude of the surface electromagnetic waves - which are induced and propagate by laser irradiation of periodical structures-riddled metallic surfaces. Also the conditions are specified for resonant incidence of laser radiation - leading to resonant excitation of surface electromagnetic waves - which were previously available only from empirical experimental data.

The utilization of pulsed lasers in speckle pattern photography (SPP) permits the contactless determination of displacement and rotation velocities, deformation rates, vibration amplitudes and other mechanical properties on nonprepared surfaces of dynamic solid state objects. The scope of efficient usage of dynamic SPP depends on laser parameters as pulse width, pulse energy and distance between pulses and on the character of the object motion. A survey about measurement capabilities and limitations is given including measurement intervals and attainable illumination areas, taking into account recent results from static SPP. Both double-pulse and time-average techniques for nonperiodic processes are refered to.

The transfer of energy from a laser beam to a solid takes place via excitation of the electronic system. At first sight, one would expect that electronic effects might play an important role in the laser-assisted phenomena in materials. Except for very short laser pulses (in the picosecond pulse duration range), experiments show that this is rarely the case. However, evidence for nonpurely thermal effects has been obtained in some circumstances. Analysis of the microscopic mechanisms involved indicates that localised states are always present (at least at some step) in the above mentioned cases. This plus a theoretical examination of the criteria for the existence of electronic effects leads to the conclusion that electronically excited localised states are responsible for various laser-assisted phenomena. In order to arrive to a good understanding of these effects, a model for the cohesion of electronically excited localised states is first given. The theoretical model is then applied to various laser-assisted phenomena: surface reactions, oxidation, nucleation and growth, damage and aging. For surface reactions, photons may excite some reactive species selectively. This is introduced in the kinetic equations of some reaction. It is found that it is possible to describe various cases of reaction rates versus incident laser fluence by using the theory. Laser-assisted oxidation is studied in the framework of the Deal-Grove formalism, modified in order to take into account localised electronic excitation. The problem of laser-assisted damage and aging is approached theoretically via the migration of defects or impurities.

The role of surface chemical reactions within semiconductor processing is considered by way of two recently studied systems. The first is the reaction of chlorine with indium phosphide, which underlies the direct "dry" etching of the semiconductor material. The adsorbed states which form have been studied at a molecular level and the results discussed in terms of thermally driven etching schemes. In addition non-thermal stimulation of reactions at the halogen-semiconductor interface is considered and results for ion beam enhanced processes are presented. The second system discussed is Al deposition from trimethyl aluminium on Si. Phases formed at the semiconductor-vapour interface are characterised and the thermal decomposition routes leading to aluminium deposition have been studied. The influence of UV irradiation on the processes occurring are identified.

Various nonlinearities in single mode optical fibers have detrimental effects in multi channel coherent communications systems. The dominant nonlinear processes are four wave mixing (FWM), stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS). These lead to crosstalk between channels, power losses, and deleterious phase fluctuations, which in turn limit the power of the transmitted light, the number of allowed channels and dictate the channel allocations. After reviewing the basic principles of the relevant nonlinear processes, laboratory experiments are described and the results are presented.

Optical processing of light with complicated statistics having coherent, chaotic and squeezed features are considered by a unitary method using the characteristic function description of the statistical properties of light.

Double-exposure holographic interferometry in BTO photorefractive crystals using He-Ne laser (40 nIV ) light was demonstrated . The recording intensity, determined mainly by the reference beam, leads to a recording time of A,5 sec. This holographic interferometer can display continuously the interferograms on a TV-receiver. Experiments for the measurement of Young's modulus show the good reliability of the method and instrument. It is well known that double exposure holographic interferometry allows high precision measurements of small surface displacements produced in the analyzed real object by external force, When the analyzed object has a simple shape (for example, cantilevel beam), one can calculate static Young's modulus from measured displacement of the object's surface under definite external stress. In order to carry out automatization of the measuring process for different samples, it is necessary to record and reconstruct holograms several times per a minute, i.e. to obtain automatically double-exposure holographic interferograms. This can be done using photore-fractive electrooptic crystals, which are one of the best reversible media for the record-ing of dynamic hologram. We have used automatical holographic interferometer with a photo-refractive Bi₁₂T10₂₀ (BTO) crystal for experimental investigation of some solids, The BTO crystal is the most sensitive among photorefractive crystals for red recording light. Hence, it is possible to use a He-Ne laser (632,7 nm) as a coherent light source in the inteferometer.

We investigate the propagation of nonlinear guided waves in two different prism coupler configurations. Both, the radiative decay features of these waves and their potential excitation by incident Gaussian beams have been monitored by a numerical simulation tech-nique.

We review third-order nonlinear guided wave phenomena in planar optical waveguides. The phenomena to be discussed include: propagation effects, e.g., stability of the nonlinear guided waves, effects of linear absorption, nonlinear saturation, multi-soliton emission and the external excitation of these new waves with flux-dependent field distributions. We also present recent numerical studies of the nonlinear dispersion curve and electromagnetic field distribution of nonlinear surface-guided waves in a semi-infinite superlattice structure in contact with a semi-infinite nonlinear optical substrate.

Different methods of obtaining high birefringence in optical fibres are analysed, especially for elliptical core fibre,PANDA type and bow tie fibre. New analytical method of boundary elements /BEM/ has been adopted for strenght component calculation and accuracy of 0,05% in comparision with cylindrical fibre calculation has been obtained. Fibre with elliptical core and elliptical inclusions has been analysed. Three experimental methods for state of polari-zation /SOP/ in the fibre have been developed namely compensation, dynamical and external magnetic field method. Obtained experimental results for different types of fibres are displayed.

The holographic stereogram is synthesized from a series of ordinary photographs, and is a very attractive medium for displaying 3D images. This paper presents a method of synthesizing a cylindrical hologrphic stereogram with white light reconstruction called multiplex hologram, and fundamental properties of reconstructed images such as distortion and resolution. An application to 3D display of medical X-ray images is proposed.

A multichannel TEA nitrogen laser has been realized for some optical diagnostics. The following methods have been applied on the plasma focus device (PFD): interferometry, schlieren, shadowgraphy and a new combination of the last two. The background of these methods and some qualitative and quantitative results obtained in plasma focus (PF) studies are presented.

The computer vision is becoming an essential feature of the high level artificial intelligence. Laser imaging systems act as special kind of image preprocessors/converters enlarging the access of the computer "intelligence" to the inspection, analysis and decision in new "world" : nanometric, three-dimensionals(3D), ultrafast, hostile for humans etc. Considering that the heart of the problem is the matching of the optical methods and the compu-ter software , some of the most promising interferometric,projection and diffraction systems are reviewed with discussions of our present results and of their potential in the precise 3D computer vision.

Some gas phase irradiations under continuous wave infrared conditions [CW laser] and pulsed ultraviolet conditions [ArF excimer laser.] are presented. The amount of energy absorbed by CO₂-the gas phase system irradiated by a CW CO₂) laser of several hundreds watts of output power, depends essentially on the thermodiffusivity of the absorbet. Therefore this parameter affects dramatically the overall decomposition kinetic of any species irradiated by a powerful infrared laser. With binary gas mixtures of absorber coupled with reactant, in the conditions of a photo sensitized decomposition, the distribution of the energy which is captured, between the two partners, leads to a maximum reaction rate at a given pressure of reactant. When the ultraviolet laser irradiation of various species at 193.3 nm is assisted by a CW infrared irradiation,different effects are observed, depending on the nature of species. The dual irradiation of NO in presence of SF ₆, enhances strongly some fluorescence emissions which can be six fold more intense than in presence of a sing1₆ ultraviolet laser irradiation. This effect gives an estimation of both the heat bath temperature and the average number of infrared photons absorbed by NO via SF6. With CF0C1,, the infrared assistance leads to a new ultraviolet fluorescence emission, equivalent to aA average tbsbrption of five infrared photons and one ultraviolet photon. This new emisssion which corresponds to the fluorescence of the state C1₂ (1 lai+-4*XlEg+), should be the indication of a strong enhancement of one path among the two decomposition channels, driving to the CF₂ radicals formation.

The paper concerns with qualitative laser induced fluorescent spectroscopy of the atomic systems in a H.C. electric discharge plasma. Some effects of a neon hollow, cathode plasma - He-Ne laser interactions, are shortly presented. We can see how the stimulated processes perturb selectively the nonlasing high levels and allow to investigate the dependence of upper or lower laser levels on some processes in a hollow cathode spectral source. A significant dependence on the curren intensity or elctron concentration of some Ne spectral lines intensities as NeI 5944.83 Å and Ne 6096.16 Å coupled with the laser line Ne 6328.16 under laser irradiation is marked. This behaviour of the spectral line intensities is similar to that obtained in the Ne afterglow plasma - He-Ne laser interaction.

This paper discusses three divergent examples of synthesis of materials with lasers. The three techniques are: (1) Infrared (CO₂) laser synthesis of silane (SiH4) from disilane (Si2H6); (2) Excimer (ArF) laser production of fine silicon powders from methyl-and chlorosubstituted silanes; and, (3) Excimer (KrF) laser production of fine metallic powders by laser ablation. The mechanism for each process is discussed along with some conclusions about the features of the laser radiation that enable each application.

The UV photochemistry of olefins and alkylbenzenes is described from a new point of view: the hot molecule mechanism. The hot molecule (denoted as is is formed by internal conversion to the ground state in the gas phase on irradiation with ArF laser light (193.2 nm). For the first time, dissociation rate constants for the hot molecule mechanism have been measured. The hot molecule (S₀**) has an another role. It can be an intermediate in UV multiphoton dissociation. S₀** shows strong absorption in the UV region and hence efficiently absorbs a second photon which causes dissociation. Radical fragmentations are major reactions of this new multiphoton chemistry.

A technique is discussed which allows the performance of extremely sensitive and isotope selective trace analysis. It applies resonant Dopppler-free two-photon laser spectroscopy and thermionic detection of the selectively excited and collisionally ionized species. If lasers are used whose optical frequencies can be tuned very fast from one isotopic resonance to the others, even in very small samples, isotope ratios can be determined by spectroscopic means with good precision ('optical mass spectrometer'). Before all other laser systems, semiconductor lasers meet the requirements of fast frequency tunability.

CW CO₂ laser driven reactions between sulfur hexafluoride and carbon oxide, carbon suboxide, carbonyl sulfide and carbon disulfide proceed at subatmospheric pressures and yield fluorinated carbon compounds and sulfur tetrafluoride. CW CO₂ laser driven reactions of organic compounds in the presence of energy-conveying sulfur hexafluoride show reaction course different from that normally observed due to elimination of reactor hot surface effects. The examples concern the decomposition of polychlorohydrocarbons, 2-nitropropane, tert.-butylamine, allyl chloride, spirohexane, isobornyl acetate and the oxidation of haloolefins. CW CO₂ laser induced fragmentation of 1-methyl-l-silacyclobutanes and 4-silaspiro(3.4)octane in the presence of sulfur hexafluoride is an effective way for preparation and deposition of stable organosilicon polymers.

Optical isotope shifts and hyperfine structures of stable Kr isotopes were measured by collinear fast beam laser spectroscopy. The atomic KrI5s[3/2]₂^0-5 (λ=557 nm), 5s[3/2]20 -503/2]2 ( X, =556 nm), 5s[3/2]2^0-5P[3/2]2 (λ =760 nm), as well as the ionic Kr II 4d 4D7/2 -5p ⁴P512 (λ =729 nm) transitions were studied. The current focus of the experiment is centered on sensitivity tests of the method rather than precision measurements, in view of our forthcoming on-line investigation of neutron-rich isotopes at the TRISTAN mass separator.

Tunable coherent radiation in the ultraviolet and vacuum ultraviolet has been generated by stimulated Raman scattering, by anti-Stokes Raman lasers, and by frequency mixing processes in non-linear media. The theory and experimental progress in the development of these laser-driven sources is reviewed, and examples of available systems and their characteristics are discussed. Various applications in spectroscopy of radiation tunable in the wavelength region 200-90 nm are presented.

We present a general overview of the field of light-induced drift, specializing to the case of alkali-noble gas mixtures.

This report deals with processes induced by laser light in liquids which contain selectively absorbing ions.

A 200 W cw CO₂, laser was used to evaporate high refractory oxides, for laser substrate irradiation before the deposition and for modification of the electron beam deposition process. For the laser-assisted thin film deposition processes higher values of laser damage resistance and a correlation between laser damage resistance and absorption were found.

The achievement of compact, reliable and multifunctional surgical CO₂ laser units with specialized beam delivery systems opens new prospects for extending the clinical use of lasers.

A technical report regarding three types of medical equipments with lasers of particular interest for ophthalmology is introduced, namely: tunable dye laser photocoagulator, CO₂ laser scalpel and Nd:YAG surgical instrument. Clinical results obtained using the above mentioned devices and Ar⁺ laser photocoagulator are reported, including concluding remarks about the application fields specific for each equipment.

The therapy of arthroses of the extermities includes a wide range of methods, such as: drug therapy, physical therapy, balneotherapy, surgical treatment etc.

Practical considerations associated with the XeC1 laser recanalization of human coronary arteries during open heart surgery are described.