The heating of a layer of semiconductors (Ge, Si, GaAs) was studied as dependent on the energy density of strongly-absorbed laser light using the monitoring of the layer's thermal radiation. The heating is shown to change essentially because of the redistribution of electron- hole plasma generated by the laser and because, with production, annealing or the initial presence of radiationless recombination centers.

Basic mechanisms of nanosecond laser annealing of ion-impl anted si licon layers are now well -known. It has been demonstrated1-4 that for the inci dent pulse energy density lower than the epitaxial anneal ­ ing threshold, amorphous silicon C a-Si) is parti all y transformed into a course-grai ned polycrystalline silicon CCG p-Si) in the near-surfa­ ce regi on and a fine-grained polysilicon C FG p-Si) lying under i t. Formation of the FG p-Si and CG p-Si is caused by formati on of a hi ghl y supercooled melt Csl -Si) as a resul t of a-Si melting at a temperature T which is 250K lower than the melting temperature of monocryslalli nemili con C c-Si) T and subsequent crystallizati on. It has been assumed in refs. 3,4 mlhat the pri mary melt formed in the near -surface region as a result of laser irradiation crystallizes with the formati on of a CG p-Si layer. Since the latent heat of crys­ tal lization is hi gher than that of a-Si melting C L =0.7L ), under certain condi tions the released energy may cause melli g ofcthe a-Si lying deeper. Crystall ization of the secondary melt l eads to forma­ tion of FG p-Si and the rel eased energy causes melting of a-Si. Hence, as a result of melting at the leadi ng sl -Si/a-Si interface and crys­ tal lization at the traili ng FG p-Si/sl -Si interface, a self-support­ ing propagati on of the melted layer lak es place. However , this model of formati on of the CG p-Si and FG p-Si layers does not resol ve the question of the ini tial crystallizati on stage.

This paper summarizes the careful investigation of the mechanism and basic regularities of anisotropic local melting of semiconductors subjected to light-pulse irradiation. The dependences of the density, sizes, and shapes of local motion regions on the intensity and duration of light pulses, the type of monocrystalline substrate, as well as the regime of preliminary implantation and ion type are established. The model of superheating in solid phase is used to explain the experimental results. It is shown that the main centers for liquid nuclei formation are the surface defects available before the light irradiation. The influence of the thermoplastic effects caused by both the light pulse itself and the tetrahedral covalent radius of implanted impurity is shown.

It is found that volume and refractive index are varied as a result of a photothermo-induced crystallization of glass. This effect is used to produce various optical elements on the base of photosensitive glasses.

On the base of a vacancy melt model a liquid may be described by means of a deformed crystal model. The correctness of using this model is illustrated by a number of examples with properties of liquids and solids close to the temperature of melting. The suggested model of a liquid is used for analysis of the amorphization process from melt under laser action.

In this work the conditions have been determined necessary for the realization of intrinsic optical breakdown of glasses and its regularities have been studied. Under focusing of the neodymium laser radiation in spots of 0.4-0.8 micrometers diameters statistical spread in breakdown threshold values, temporal and size dependence are absent. Breakdown threshold for glass K-8 and fused quartz KY-1 are similar and are almost 1013 W/cm2, i.e., 6(DOT)107 V/cm. Based on results obtained in this work, a model of mechanisms of intrinsic optical breakdown of glasses has been proposed.

In this work, the processes resulting in optical parameters change of glasses was investigated during the beforethreshold laser irradiation. Residual changes of refractive index resulting in beam contraction and intensity growth of laser radiation in the caustic center were found to be conditioned by the production of mechanical stresses in the sample bulk. Under multiple laser radiation with h(nu)

Thermally nonequilibrium state in metals may be created due to the action of ultra short laser pulses. This phenomena has been devoted much quantity of investigations [1,2 and see references there]. But all efforts made in this direction were connected with the heating of massive metals or metal films of big thickness which therinophysically behave as a massive sample under the short pulse action. This metal films (TNF) of thickness h1O6sm, widely used in laser technology are of great practical interest.

It has been found that the thermodeformation rise time considerably exceeds the exciting laser pulse duration when the latter is shorter than 10-6-10-5 s that has been phenomenologically described when presenting metal as a viscoelastic medium. The effect of heat-insulated defects of the metal surface layer is considered as the most probable cause of thermoelastic response inertia. A brief analysis of the application of surface thermodeformation (STD) parameters to optical elements characterization and nondestructive testing (NDT) is presented.

Characteristics of 'melting dendrites' resulting in a NaCl volume from combined heating by furnace and CW laser irradiation are studied. The dendrite growth velocity, tip curvature radius, and side branches period are connected by the relations typical for crystallization dendrites. In spite of coincidence of 'liquid' dendrites growth direction and easy glide direction <110>, no relation of their parameters with processes of plastic deformation of ambient crystal is discovered.

The effect of the formation of large-scale structures on a target surface is experimentally and theoretically studied. The conditions of structures growth as a function of the background gas pressure, laser radiation intensity, and its angle of incidence are defined. A mechanism of structure generation associated with the instability of capillary waves in the field of the laser torch pressure is proposed. A dispersion equation describing instability is obtained, whose analysis gives noncontradictory explanation of the experimental results.

Thin photosensitive films being irradiated by a feeble polarized laser beam are able to record periodic structures (spontaneous diffraction gratings). These spontaneous gratings (SG) are a result of interference between the incident beam and scattered in film wave guide TE- and TM-modes. By a character of their development, the SG in photosensitive layers are similar to surface SG induced on a surface of metals or semiconductors by a strong laser irradiation. At a number of theoretical works, a complicated self-organization of spontaneous structures accompanied by the rise of secondary and multiple gratings on final nonlinear stages of their growth is predicted. The emergence of secondary SG on germanium surface was reported in. The nonlinear stages of growth of volume noise holograms in photosensitive media also were investigated. This paper reports the rise and multiplication of SG in the AgCl-Ag photosensitive layers irradiated by polarized laser beam in the case of frustrated total internal reflection. The important role of two-dimensional Bragg diffraction of wave guide modes in formation of SG on nonlinear stages of their growth is shown.

Abstract not available.

It was shown that the threshold lowering of optical strength of optical materials under multifold pulse laser irradiation can be due to the thermodiffusion solution of the locally- heated inhomogeneities during the pulse laser action. Increasing the inclusion radius leads to increased heating and thermostrains in the matrix near inclusions up to the limit. The local heating of the inclusions is due to the recombination of photoexcited matrix nonequilibrium carriers of charge on inhomogeneities which play the role of a recombination drain.

Abstract not available.

Results of ultrashort pulse train self-diffraction are represented. Direct experiments proved the thermoacoustic nature of this phenomenon. The main features of pulse train self-diffraction (threshold characteristics, dynamics) are examined. Its influence on passively mode-locked and synchronously pumped lasers operation is considered.

Experiments investigating thermocavitation in binary solutions induced by continuous laser radiation are described. The cavitation consists in periodic rise and collapse of vapor-gas bubbles, accompanied by hydraulic shocks. The necessary condition for obtaining periodic pressure pulses by thermocavitation are investigated and the influence of the volatile component in binary solutions on the magnitude of acoustic signal is studied. Regime of cw and pulse-laser excitation of cavitation is compared.

Mathematical modeling of water droplet explosion in air in the field of CO2-laser radiation (LR) was carried out. Some processes leading to air optical breakdown (OB) initiation in shock wave (SW) were investigated. OB of shock-heated air has been shown to develop in two stages. At the first stage, initial electrons are caused by plasma chemical reactions in heated and compressed air. At the second stage, these electrons, under influence of laser radiation, give rise to an electron avalanche, which leads to air OB.

Theoretical insight into aerosol particle heating/evaporation by laser radiation takes a great deal of activity. However, detailed investigations are mainly aimed at diffusion, diffusion/convection, and gas-kinetic evaporation. The convective subsonic (and sonic-speed) evaporation of a water droplet (at the condensation coefficient (alpha) equals1) under laser radiation is considered, with the Mach number at the Knudsen layer boundary being found by means of numerically solving the non-stationary hydrodynamics equations for an external flow pattern. However, the droplet surface temperature was determined on the basis of the assumption that temperature gradients within the droplet are insignificant; as for rapid heating and convective evaporation of a droplet of a few micrometers, this assumption is not valid. This paper focuses on the influence of the condensation coefficient on the sonic/subsonic convective evaporation of a water droplet subjected to continuous wave laser radiation (or to pulses such that the phenomenon can be considered quasistationary). For these quasistationary conditions, a simple relation is derived for determining the Knudsen layer boundary Mach number. Then the heat equation with variable coefficients is solved to evaluate radial distributions.

A self-consistent mathematical model for numerical investigations of unsteady gas dynamical and optical phenomena in a low-temperature laser plasma is described. The dynamics of laser- supported detonation waves in CO2 and eximer laser beams are investigated. The results of refraction and absorption in laser plasma are presented.

Analysis of experimental studies of laser action on condensed absorbing media performed for a wide spectral range from 0.248-10.6 micrometers has revealed that the processes of starting plasma formation are identical in that they display an erosion character of the laser plasma origin and a weak dependence of the threshold of its formation on the laser radiation wavelength, which is due to the locally inhomogeneous character of laser vaporization and near-surface plasma formation.

In intense laser beams, the gas-plasma boundary turns into supersonic front of gas ionization. Front transport may be caused by shock wave, by plasma radiation, or by electron avalanche in the laser beam. Calculations show that four supersonic regimes of ionizing wave motion are possible. The properties of produced plasma depend on the regime. It makes it possible to create the plasma with definite properties for various applications.

Various applications of the multilayer x-ray optical elements for the investigation of the radiation spectrum of a high-temperature laser-produced plasma in the energy range $OM0.1-1.5 kev are considered. Experiments on the laser-produced plasma imaging and intense soft x-ray flux obtained with spherical multilayer x-ray mirrors are discussed.

Total energy involved in the process of laser pulse irradiation of coal, hexamethylene tetramine. Al, and Bi was measured. The experiments were performed with Nd-laser- generated single 50-ns FWHM pulses with peak focused intensities ranging from 106 to 109 W/cm2. It was found that the irradiation of studied materials with single laser pulse induces a release of additional energy. For fuels, the additional energy may be of an order of magnitude greater than laser pulse energy. For metals, the ratio of the additional energy to the laser pulse energy is about 0.2-0.4. Using the material removal measurements and the reference specific combustion heat of fuels, the theoretical estimations of energy produced by combustion of material removed by laser pulse were made. Theoretical estimations and experimental results are in good agreement for coal irradiated in air.

Abstract not available.

A time evolution of the space charge-layer (SCL) has been investigated under photoelectric effect from a target into N2, He, and air. The influence of an attachment, background plasma (BP), and negative ions on this process was established. At pressure range (10-3 - 10) Torr the development of the double-layer instability, which was caused by a BP-electron-gas pressure above the critical value, and ignition of arc photoelectric gas discharge were observed.

This paper reports the experimental results on measurements of both millisecond pulsed-laser radiation in erosion torch and pressures at irradiated targets. Proceeding from a comprehensive analysis of possible mechanisms of onsetting pressure oscillations on irradiated targets, the gas dynamic mechanism of pressure oscillation generation has been proposed and experimentally confirmed.

Experimental investigation results of plasma characteristics formed on a solid-state obstacle surface during ambient optical breakdown under the influence of a powerful pulse CO2 laser are given. The results touch upon the problem of three aspects: a front motion velocity of formed plasma radiation interaction. The effect of energy density (or average power) in an irradiation spot, an obstacle material, and a laser pulse shape (length) on the process characteristics is an order of 10 cm2 that makes it possible to neglect two-dimensional effects.

A phenomenological model is suggested for near-surface laser plasma initiation for the case of short durations of the ignition process (t*-7 sec). The model takes into account the dependence of the surface defect's absorptivity on its size and the local concentration of defects. A comparison of calculated and experimentally obtained values of plasma initiation duration is carried out.

The spectrum has been calculated numerically of the radiation from aluminum plasma produced by a moderate-power CO2 laser. These calculations and experiments with the pulsed CO2 laser show that the main part of the thermal plasma radiation falls at photons with energy more than 11 eV. It is shown for the first time that, upon exposure of the target to the CO2-laser radiation, the efficiency of the conversion of the laser energy into that of the thermal plasma radiation is higher than in the case of a neodymium laser under the same conditions, and amounts to about 30-50%.

Experimental data are given concerning plasma air breakdown near the surface of samples made of different materials, depending on energy density and length (shape) of TEA CO2 laser pulse in the range of 1 divided by 40 J/cm2 and 2 divided by 8 microsecond(s) with the spot radiation size of 10 cm2. Energy thresholds of the plasma arising and their dependence on laser pulse length are determined. Experimental data are given concerning energetic balance components of laser pulse interaction in the conditions of plasma forming: energy outlay for plasma forming, losses due to plasma radiation, and thermal flow into sample. With these data in mind the energy part of the laser pulse absorbed by sample and that dissipated into surroundings are determined.

Based on measurements made by the intracavity laser spectroscopy method, quantitative diagnostics of laser erosion plasma has been performed at stages of low-threshold near-surface optical breakdown and afterglow: dynamic fields of densities of target material atoms and ions (Al and Ti) have been constructed (1011 - 1016 cm-3), electron density has been measured (approximately equals 1018 cm-3), and plasma temperature has been determined (approximately equals 25 kK).

A study of generation and structure of magnetic fields in plasma, formed by radiation of moderate power on the surface of a dielectric barrier, is conducted. The parameters of magnetic fields in laser-produced plasmas are found by numerical solution of the known system of equations considered in a two-dimensional cylindrical configuration and also by experiment. The temporal and spatial distributions of magnetic fields and the correlation between the magnetic field and laser beam parameters are considered.

A highly sensitive method for the detection of photodissociation (PD) of absorbed molecules has been developed using the surface ionization process. Spectral, temperature, and polarization dependences of the PD yield were measured in the quantum energy range of 0.6 < hv < 4eV and PD cross-sections were evaluated for single CsCl, CsBr, and CsI molecules on the surface of a graphite monolayer on iridium. The PD process, due to photoexcitation of absorbate molecules, was found to be of a one-quantum nature. The dissociation energy of single-absorbed molecules, as well as their orientation on the surface, were determined.

For some crystals with ionic-covalent bonds (AgHal, CdS, ZnS) under the action of UV- radiation large light fluxes, a decrease of steady luminescence is revealed that is stimulated by the formation of absorbed small atomic clusters playing the part of electrons and recombination centers. The formation of these clusters is explained by the availability of a photosimulated surface migration of absorbed silver, zinc, and cadmium atoms and ions. The electronic and acceptor properties of the absorbed atoms and clusters are studied, and the activation energies of the particles' photostimulated migration are measured. This work suggests the mechanism and the kinetic model of this migration.

Isothermal and laser copper oxidation kinetics are investigated by optical method in the range 200 degree(s)C - Tmel. A measurement method to determine optical constants of a formed oxide film by the values of absorptivity in points of local extreme is suggested. It's shown that at T > 480 degree(s)C, the laser oxidation rate exceeds the isothermal one. Laser oxidation rate depends on a type of formed oxide. This effect is explained in a terms of a thermal-EMF mechanism.

Experimental investigation of the optical film density of light sensitive complexes depending on absorbed laser flux density was carried out. The effects were observed to be either oscillating or extreme. The threshold mechanism of induced laser-chemical changes also was detected. The qualitative model of the observed phenomena is given here.

The electromagnetic field distribution in the corrugated-metal semiconductor system was computed. When the reciprocal grating vector equals the difference of wave vectors of the surface modes at the two interfaces of the metal film, the effective resonant tunneling of the electromagnetic field through the metal film is possible. Used as selective photodetectors or light emitting devices, this may substantially increase the efficiency of the mentioned structures.

Experimental investigation of ordered and disordered surface structure formation under the pulse laser radiation effect of titanium and zirconium metal surfaces primary in oxidizing environment are presented. A model for qualitative explanation of formed structures is proposed. The occurrence of dilate stress fluctuation will induce the vacancy concentration growth that consequently results in tensile stress growth.

All types of periodic structures, which are formed on semiconductor surfaces by the pulsed laser radiation with photon energy h(omega) > Eg (Eg equals gap energy), may be classified in two large groups: (1) Resonant periodic structures, which form as a result of the interaction of an incident light 'pump' wave and a surface electromagnetic wave (SEW). The period of these structures is determined by the wavelength, angle of incidence, and polarization of the incident radiation; (2) Non-resonant periodic structures, with the period which is not directly associated with the parameters of laser radiation. The orientation of these structures is, as a rule, determined by the crystallography of the irradiated surface. In the case of the laser pulse duration (tau) equals 10-6-10-9 s, the forming structures were usually of resonant type, while for non-resonant structures the pulse duration was about 10-2-10-4 s. This paper reports the results of the experiments on irradiation of silicon samples surface by the laser pulses with different types of the polarization. They indicate that the properties of non-resonant structures at several orientations of the electric field vector of the light wave Eyields with respect to some crystallographic directions on the surface depend on polarization. The peculiarity of the formation of resonant periodic structures at the large angles of incidence also is examined.

This paper presents the results of studies carried out by the authors on the impact of nonlocal scattering upon spatial and time distortions of laser radiation signals mirror-reflected from gratings of a sinusoidal profile and diffusely reflected from rough metal surfaces.

Heterodyning surface electromagnetic wave (SEW) interferometer for measuring SEW phase velocity and the corresponding metal plasma frequency is described. Plasma frequency measurements for gold and copper are reported.

The results of YBa2Cu3O7-x films on SrTiO3 investigation by far infrared surface electromagnetic waves (SEW) amplitude and phase spectroscopy at temperatures 80-350 K are presented. Strong SEW absorption at frequency 140 cm-1 has been observed. The origin of the observed absorption is proposed to be concerned with slab-phonons in YBa2Cu3O7-x. The optical constants of the films have been obtained. The complex SEW refraction index on temperature is explained, taking into account 'soft modes' features in SrTiO3 substrate. It has been determined that only the imaginary part of the SEW refraction index changes when the film transits into superconducting state, while the real part remains unchanged.

An experimental investigation has been performed of sulphur hexafluoride molecules separation by diffusion through a metallized fine-porous membrane in the field of surface electromagnetic wave (SEW) induced by CO2 laser radiation. Dependencies of SF6 mixture separation coefficient are obtained upon different parameters: SEW intensity, isotropic composition, and pressure of the initial mixture. The influence of an inert gas admixture upon the separation efficiency is studied. A possible mechanism of heterogeneous separation of molecules induced by SEW is suggested.

Abstract not available.

Ferroelectrical phase transition, induced by laser nonthermal action, has been observed and studied in Ge-doped quartz. Optical second harmonic generation (SHG) is used to study the tensor of the nonlinear susceptibility that reflects the symmetry of the ferroelectrical phase. The maximum value of the tensor component calculated from the experimental data is equal to 2 10-12 m V-1. The increased dielectric constant of new phase has been also observed. The direction of the laser induced anisotropy has been determined by the laser pulse polarization. The effect of the laser-induced diffusion of impurities in transparent dielectrics has been described in cases of Ge and W.

The dynamics of surface relief changes and thermal deformation in semiconductors are investigated with respect to radiation power density during laser pulses. A thermomechanical model of periodical relief formation is suggested.

From the very moment that generation of spontaneous magnetic fields (SMF) in laser plasma has been found experimentally, this phenomenon was treated in a considerable number of publications. These studies were dictated by the importance of this phenomenon for controlled thermonuclear synthesis, as well as for generation of low-frequency currents and fields in a laser flame, from the viewpoint of the conversion of laser radiation into electric energy. The SMF generation mechanisms are rather well explored now. At the same time, the authors believe the available results fail to provide a wholistic and completed picture describing the above processes. In particular, not enough consideration in literature has been given to problems of spatial distribution and time behavior of fields inside and outside plasma with respect to its dynamic and geometric characteristics, as well as problems pertaining to propagation of SMF through conductive shields. This paper attempts at clarifying, to some extent, these topics theoretically. This paper considers part of the field for which the scales of the respective relationships have the same order as the orders of the size of the area occupied by plasma and the time of its life. It is evident that such a field, which is called large-scale, may be obtained by averaging the true field over its fluctuations fast enough in space and time. Clearly, all small-scale components of the field, as they leave plasma, die away very quickly and the outside field becomes fully large-scale. A large-scale magnetic field is characterized by plasma state of a weak nonequilibrium and by processes of charge emission from the laser target. From the viewpoint of macroscopic electrodynamics, the sources of such field are described by density of extraneous currents.

Abstract not available.

The thermoelectric voltage induced in the slant-angle deposited metallic films by light has been investigated. It is found that the magnitude of this voltage depends on the surface morphology and the width of the films. The physical models of this phenomenon discussed in the present work permit choosing of the optimum geometry of the film layer in manufacturing non-selective detectors of radiation.

The heating of free carriers by the infrared (IR) radiation or electric field increases the average energy of the carriers. This constitutes the physical basis for the observed photovoltage in semiconductor contact structures. In the present review the experiments carried out in recent years with semiconductor diodes and transistors are described. This allows the main properties of internal photoemission, photocapacity effect, and secondary carrier injection to be determined.

On the basis of numerical calculations, it is shown that the pressure and temperature in laser- generated shock waves in graphite can achieve the values according to the steady existence of diamond phase. The parameters of laser radiation, at which the shock waves have the necessary intensity, are defined.

Increasing attention been given lately to focused on the laser—induced transfer technique in which metal coating are formed on the localized surface areas [1,2,3J. Resent interest in this technique has been spurred by its perspective to become an alternative for the well—known methods of local coating formation which are based on metal deposition out of photolitic, pyrolitic and photothermal liquid or gas metalliferous compounds [4]. Physical process which is the basic of the forward transference technology is the so called "The Laser—Induced Forward Transfer (LIFT) technique, and it includes 2 steps which are independent at the first sight: — thermal damaging of the donor film, deposited on the transparent insulative substrate, which was induced by radiation of the pulsed laser directed from the substrate; — depositing the products of destruction on the acceptor substrate. The difference from the well—known laser—beam evaporation methodic that the substrate (acceptor) is disposed in parallel to the target(donor) at a distance of one order, where the diameter of the laser—beam radiation zone is usually 10-100 mkm. According to on the analysis of the publications, in which the problem was studied, it may be concluded that the transfer process model has not been well formalized yet. Also, the process itself is poorly reproducible, and it is difficult to optimize it practically. In this paper we propose a mathematical model of the process. Accordingly. all the steps of the process are presented as a closed system, which varies with the time.It is therefore possible to provide single—valued interpretation of the result of simulation and experiment.

The discovery of polymer ablative etching by far-ultraviolet (UV) excimer laser pulses has given rise to a wave of publications devoted to the investigation of the etching mechanism and applications of this phenomenon. Against this background, the studies in which the action of continuous UV-light on polymers is examined are less noticeable. They include the direct photoetching under UV-lamp irradiation and the direct writing by a cw laser beam on a polymethylmetacrylate (PMMA) film and some other polymeric materials. One can expect that laser writing on the polymer film will find its application in local area processing and custom patterning. The purpose of this work is to estimate the direct writing abilities for simultaneous photochemical and thermal action of a laser beam on PMMA.

Some aspects of the laser light-polymer resist interaction are discussed. A possible way to increase the sensitivity and contrast is shown. 1. The laser chemicai technologies are widely used in indust- ryfi]. Here we analyze the laser capabilities of solving some elect- ron and roentgenolitography problems. It is shown, that the problems of polymer resist low sensitivity and contrast can be solved by light modification [2, 3].