It is well known that under the action of external energy fluxes a large number of voids are being formed in solids. Thus, intense voids generation takes place after the ion implantation, high energy particle irradiation and laser irradiation. A common feature of all these cases is the generation of a large number of nonequilibrium vacancies. The cause of the void formation is condensation of these defects into the clusters which are the embryonic voids. The classical theory of void generation has very limited validity in the above mentioned cases due to the very high vacancy concentrations and nonequilibrium conditions of their generation. Besides, a sharp threshold character of the void formation phenomenon, that is observed in experiments cannot be explained from the classical (thermodynamic) theory point of view. In this report a novel vacancy-strain (VS) mechanism of the nonequilibrium threshold formation of voids in solids is proposed.

The process of periodic structure formation on the GaAs surface by laser induced wet etching has been investigated. The exponential growth rates of the structures were measured in situ for the first time. The influence of the various etchants on the relief spectrum has been studied. Phased diffraction gratings with controled periods in 0.35-0.5 μm range have been obtained. The physical mechanism of this phenomena was established by the comparison of the theoretical and experimental results.

We synthesized stable and adherent TiSi₂ layers by one-step excimer-laser irradiation of Ti films deposited on Si wafers. By multipulse laser irradiation a regime was got when Ti covering Si windows, opened into SiO₂ layer grown on the Si substrate, was completely reacted, while the neighbour Ti covering the SiO₂ interlayer was entirely expelled. This means that a self-aligned silicide layer (salicide) was formed. Moreover, it is shown that by mulitpulse irradiation of Ti/Si samples in nitrogen atmosphere, it is possible to obtain multilevel TiN/TiSi₂/Si structures with titanium silicide formed at the Ti-Si interface and titanium nitride formed at the Ti surface.

Recent results obtained in our group on double pulse KrF (248 nm) excimer laser etching of silicon in Cl-containing gases are summarized and discussed in context of previous studies. The reaction of Si [111] with Cl₂ and CCl₄ under the action of KrF laser radiation using a new double pulse technique has been investigated. The reaction and adsorption times were determined for both gases under high pressure conditions (1-100 Torr). The proposed tandem pulse technique with a variable delay between pulses can be used to explore the gas-surface interaction parameters of deposition as well as etching processes.

The concept of field-assisted etching is developed. Numerical solution is obtained for the equilibrium flux of negative halogen ions through a thin (h ≤ 10 Å) buffer layer of reaction onto the surface of silicon of various bulk dopings. Results of the numerical simulation are compared with the experimental data.

The present article contains the description of simple experiments and their theoretical interpretations mounted for demonstrations of temporal and spatial structures (regular, stochastic and chaotic) of nonlinear dynamical systems. Results of three different types of experiments are presented: a) Nonlinear oscillations and current fluctuations in V₂O₅ single crystals (n-type semiconductors) in external magnetic field. b) Self-sustained oscillations of heat field appeared on the surface of metallic vanadium plates during their oxidation processes under influence of cw IR laser light. c) Excimer laser induced modification of polymers yielding synergetic type surface structures.

The action of powerful laser radiation on superconducting materials is very important for different applications. Laser ablation was successfully used for the deposition of thin superconducting films, and for thin film patterning. Laser modification of thin superconducting films without any ablation of material has been also demonstrated. This work presents the results of our experimental and theoretical studies of the laser induced decomposition, evaporation, and ablation processes in 1-2-3 superconductors. A model of powerful radiation action on 1-2-3 superconductors has been developed. Low energy mechanism of ablation is developed and the, a processes of modification of thin films and drops generation during film deposition have been explained.

Laser ablation of a target and subsequent deposition of films is a widespread method of high temperature superconducting (HTSC) thin films fabrication. High intensity of laser light acting on the target ensures the provides high concentration of excited atoms and ions, that allows the reduction of the temperature needed for the epitaxial growth. High density of the evaporated materials stream near the substrate gives the possibility of fabricating very thin and unbroken films. All this features of laser assisted materials deposition allow the preparation of the epitaxial HTSC thin films of very high quality. In this article we briefly report the results of the conservation of stoichiometry in the deposited films. High temperature of evaporated materials in the laser plume application of lasers for HTSC films creation, their testing and structuring obtained in Moscow State University.

Under UV radiation new absorption bands and photoinduced paramagnetic color centers (PPCC) may appear in a silica glass (v-SiO₂) and density of material may increase. These effects must be accounted for in developing laser optics elements based on silica glass, fiber waveguides for UV spectrum range, or in the production processes of the microelectronic components, using the Si/SiO₂ films.

Possible mechanisms of tearing off and transference of the film from the donor substrate (target) to the acceptor substrate as a result of a local laser action are considered. Thermal, gas-dynamic and hydrodynamic models for explanation of a number of effects observed at local laser film deposition are proposed. The range of technological parameters close to optimal ones is determined.

The technological process of laser head production involves cleaning the device parts from all kinds of contaminations. After the assembly of the device, the vacuum surfaces are inaccessible to cleaning by traditional methods, yet ten percent of optical components show contamination in the aperture zone after assembly. These contaminants are kept on the optical component surfaces by electrostatic forces which resist even strong vibrations and shocks. Various methods of surface cleaning with a laser beam are known from the literature, but all involve external surface cleaning. The present problem consists in performing the laser- induced cleaning of the precision optical surfaces in a vacuum, through the material of optical components, without inducing any changes in these optical components. The analysis of this problem, the spectral characteristics of optical component materials (fused silica, multilayer dielectric coating materials), and the spectral characteristics of potential contamination materials, has led us to the following conclusions: (1) the wavelength of processing radiation must satisfy the condition of optical component material transparency; (2) the intensity of processing radiation must be less than that of optical component damage threshold; (3) the radiation must be well absorbed by the contamination material; (4) the radiation wavelength must be as short as possible.

The structure and also the phase and element composition of the technically pure iron samples have been investigated before and after the exposure to laser pulse radiation by the methods of metallography, Moessbauer spectroscopy, electron microscopy, and x-ray micro-analysis. It has been shown that carbon in the untreated samples is distributed inhomogeneously and is concentrated in the intergranular areas of crystals. After laser treatment with alloying of the surface, carbon concentration in the α-Fe crystals increases four to five times, while the amount of carbides increases two times. The increase of carbon concentration and the amount of the carbide phases in α-Fe under the influence of laser radiation is caused by rearrangement of carbon in the affected zone. With the use of the concentrated energy beams, one can create the surface layers in solids, with substantial operational advantages to the layers obtained by chemical-thermal treatment. One of the prospective methods of laser technology is implantation of doping elements into the host metals and formation of doped layer. The structure, phase composition, and properties of the affected surface layer depend not only on laser irradiation conditions and composition of the doped layer, but also to a considerable extent on the structure and composition of the bulk material. Mass transport and mixing, not only of atoms of the doped layer but also of the elements from the bulk, take place in the zone of thermal treatment. This is important problem is, however, insufficiently covered in literature. Carbon plays a particularly important role in iron compounds, since even a small amount of it greatly affects alloy properties. Therefore, with the study of laser implantation it is convenient to use as the host material the technically pure iron which contains a low quantity of impurities, including carbon. This allows one to ignore the interaction of impurities with doping atoms when considering mass transport of the implanted elements and the crystallization process. The aim of the present work is to investigate formation of phases and structure elements under the influence of laser radiation and carbon distribution in the untreated and affected samples of technically pure iron.

The powerful sources of UV radiation on a base of discharge excimer lasers find wide application in scientific research and technology. Short wavelengths, high peak and mean powers, and the possibility of quick working mixture exchange are making this type of laser extremely attractive for photochemistry, lithography, and laser medicine. Nevertheless, it is known that without taking special measures, excimer lasers possess bad spectral and spatial coherence. Further progress in the growing field of excimer laser application is impossible without flexible control of radiation parameters: linewidth, divergence, and laser pulse duration. The authors investigate different approaches to producing radiation with high spectral and spatial brightness as well as with variable pulse duration from commercial excimer lasers. The experiments were carried out on a commercial excimer laser Model 1701 developed in the Physics Instrumentation Center of the General Physics Institute. The laser discharge volume was 1 X 2 X 60 cm³, the output energy is 200 mJ at 248 nm and 100 mJ at 308 nm. Maximal repetition rate is 50 Hz.

This paper describes the application of two surface sensitive optical techniques to the study of III-V growth under MOVPE conditions. The first technique, optical second harmonic generation, is shown to be well suited to in-situ MOVPE studies of III-V growth, despite the fact that typical substrates should give rise to intense bulk SHG signals. Model SHG studies of GaAs (100) are described which allow the proposal of a suitable experimental geometry for the application of this technique to a substrate in an MOVPE reactor. Reflectance anisotropy measurements have been made from a GaAs (100) surface in an MOVPE reactor during a series of pump-purge cycles commonly used to remove volatile contaminants from the reactor prior to MOVPE growth. The RA response observed from the substrate at 300 K varies in intensity with both the number of pump-purge cycles and the extent of evacuation reached in each cycle, suggesting that a change in surface structure or composition may be induced via evacuation in an increasingly cleaner reactor environment. RA data recorded during a pre- growth substrate bake in arsine clearly show the onset of the formation of an As-stabilized surface at temperatures around 670 K, where the decomposition of arsine becomes appreciable. Temperature-programmed desorption from the resulting As-stabilized surface reveals an initial loss of As from the surface commencing at low temperatures (470 K) followed by recovery of the As-stabilization at higher temperatures (670 K) due to arsine decomposition. These data are compared with data for As-desorption from GaAs (100) recorded during MBE growth and it is shown that inflection in the RA traces could relate to surface reconstruction changes occurring under these high overpressure conditions.

We report here the experimental results on the SHG and linear reflectivity studies of the dynamics of laser-induced melting of a GaAs surface layer under subpicosecond pulsed laser excitation. We find that the SH intensity drops in a time less than 100 fs after excitation, while the linear reflectivity reaches a value characteristic of molten GaAs on a time scale of about 1 ps. Thus, the experimental results unambiguously indicate that ultra-fast phase transition to a new solid phase with structural properties different both from that of initial material and that of molten GaAs takes place in the surface layer under strong femtosecond laser excitation. This transition occurs on a time scale of 100 fs which is about an order of magnitude less than the time required for the electron relaxation to the bottom of the conduction band.

Nonlinear absorption of 176-fs laser pulses in GaP was measured using both time-domain and intensity-domain techniques. The nonlinear response turned out to have a very short relaxation time. The absolute value of the two-photon absorption coefficient was measured.

The results of theoretical and experimental studies of the influence of crystalline structure on the nonlinear optical response of both metals and semiconductors are presented. It is shown that lattice disordering leads to the decrease of both anisotropy and the absolute value of the quadruple second order nonlinear susceptibility in aluminum and third order nonlinear susceptibility in silicon. These results are in agreement with experimental data.

Nonlinear behavior of optical properties of PnSnTe epitaxial structures excited by CO₂ laser pulses is investigated. Fast optical switching and bistability are observed. Numerical modeling of the experiment with an account for the dynamics of the noneuqilibrium carriers and the sample temperature is performed. Carrier-induced nonlinear refractive cross-section of the studied compound is determined.

A new method of film structure monitoring is proposed. It is based on the analysis of second harmonic (SH) radiation induced in a film irradiated by a laser beam. SH intensity measurement versus angle of the plane of polarization of the incident light and versus film thickness provides the information about film crystal quality, presence of polycrystalline component and crystallographic axes orientation. This method can be complementary to the well-known ones and is especially suitable for research groups since it allows a correlation between technological and crystallographic parameters to be quickly determined.

An analysis of the current state and prospects of optical correlation systems for structure diagnostics of rough surfaces is given. Several studies resulting in the development of devices for diagnostics of weakly rough surfaces are briefly described.

The present paper contains the main results of the problem solution for focused laser beams diffraction on moving rough surfaces. The scattering space is considered to be nonlinear and inertial system, the input signal is the function, describing surface profile, and response is the fluctuations of scattered wave intensity. On the basis of results obtained the mechanisms of output signal formation in dynamic system are investigated and output characteristics analysis is made. The metrological possibilities of triangulation method adapted to surface microprofile measuring are discussed.

The peculiarities of partially developed speckle fields formed by focused laser beam diffraction on rough surfaces are considered. The methods of profile and surface roughness parameter measurements are discussed and their characteristics analyzed. The process of dynamic partially developed speckle fields applied to velocity and vibration parameter measurements of scattering objects "in the point" are investigated.

Experimental results on energy and polarization characteristics of the radiation reflected by a layer containing oriented particles are presented. Two models of surface layer are considered: isotropically absorbing particles (model 1), and anisotropically absorbing particles (model 2). Model 1 refers to a layer containing (gamma) -Fe₂O₃ particles with different orientations. Estimates of the particle orientation degree were made from the photomicrographs taken at 1030x magnification. Model 2 refers to a polaroid film containing fully oriented (B equals 0.99) needle-like herapathite microcrystals.

The method of thin foil thickness and optical constants' simultaneous determination is proposed. These parameters are found by measurement of the light incidence angle in the attenuated total reflection (ATR) geometry corresponding to zero reflection (ZR) for different dielectric coatings on the ATR-prism base. Recently the excitation of surface plasmons (SP) by ATR has been applied to the investigation of surfaces of solid and thin films. The advantage of this method is the high sensitivity of SP to the surface state. Unlike the ellipsometry, the ATR method requires no phase difference measurement that essentially facilitates the measurement procedure. Two main schemes of the ATR method are that of Otto and of Kretchman. The scheme of Otto allows the investigation of a wider class of objects than that of Kretchman, but its application is dependent on the precise determination and control of the gap between the prism and the sample. For the solution of this problem, an elegant approach was suggested of finding values of the gap and the angle of the light incidence on the prism where the reflection coefficient equals zero. Thus the parameter to be measured is the light incidence angle. In this work, the analysis of measurement accuracy for film thickness and optical constants by the ATR ZR method is carried out and a new method is suggested allowing considerably more accuracy.

A phase sensitive scanning fiber-optic microscope is described. Confocal operation with single mode fiber acting as a spatial filter is demonstrated. Application of two mode optical fiber for the differential imaging is proposed.

In addition to conventional optical methods for surface studies, various differential phase optical techniques have been developed recently which are capable of detecting variations in optical path length with very high sensitivity (up to 10 angstroms according to theoretical estimations). The differential approach is based on the measurements of phase difference between two beams reflected from two adjacent points of a sample. It results in high depth resolution, but the system response is fairly simple only for step-like structures. The authors propose a novel technique for recovering the surface optical phase relief by numerical treatment of experimentally measured differential phase scan. The image formation theory of the differential phase optical microscope (DPOM) described by Chung is developed and the differential phase scan is -- under certain assumptions -- the finite derivative of the convolution between the phase relief and the amplitude profile of the optical beam on the surface. The experimental data treatment includes the appropriate numerical method for solving the ill- conditioned integral equation to obtain the surface phase relief. This technique has been applied to studies of the refractive index profile of ion-exchanged channel glass waveguides and the surface profile of Ti:LiNbO₃ channel waveguides.

The paper presents an optical scheme for a precise focusing method. The beam reflected from the detail interferes with a reference beam, and optimal parameters for the optical scheme are calculated. It was found that the optical scheme sensibility does not depend on the focusing distance of the second objective.

The authors discuss the problem of polarized laser beam diffraction on extended rough plates with a regular structure. Using the method of equivalent sources, they arrive at the simple approximate formulae for Muller matrix elements valid for wide beams scattered by the samples with small periodic profile surfaces. For the calculation of other parameters, the widely known algorithms for the plane electromagnetic wave diffraction on the unlimitedly extended rough plates of the same structure are used.

At present, the intracavity diaphragming method is usually used for the selection of transverse modes of gas laser cavity with a hard diaphragm being placed inside the cavity. Its position and size are determined theoretically. Narrowing of the working canal of a gas-discharge tube to the necessary dimension may also be used as a diaphragm. The above selection method has a number of disadvantages, essentially affecting manufacture of the device and its parameters. The aim of this work is to investigate the possibility of transverse mode selection in a gas laser cavity with methods of laser technology. This approach to selection mode problem differs from previously known ones in that the selection process takes place in the assembled emitter.

Experimental results of FIR ((nu) equals 85 - 142 cm^-1) surface electromagnetic wave propagation in n-type semiconductors (InSb, GBaAs, InP) and ferroelectric films Ba_xSr_1-xTiO₃ are presented. A technique for measuring the plasma frequency (nu) _p and the damping constant of plasmons (gamma) (or the concentration and relaxation time of electrons) in doped semiconductors was designed. The SEW propagation distance dependence on electron concentration in GaAs has been obtained. The relationship between the SEW propagation distance L and the 'soft mode' parameters in ferroelectric films was found. In the L dependence on temperature the minimum was observed at T equals 380 K in Ba_xSr_1-xTiO₃, which is explained by the increase of dielectric losses tan (delta) in the film under phase transition.

Holographic methods have been widely used in surface testing, the principal methods being the recording and reconstruction of the information on the surface under investigation, the measurement of the changes of the surface and the surrounding medium, and the holographic interferometry. The holography without reference beam (HWRB) has received little attention in this respect, although it possesses all the advantages of the commonly used holographic methods. Some of the applications of the HWRB and the holography with a local reference beam have been reported in the literature. The present paper is an attempt to investigate the applicability of the HWRB for surface testing. The feasibility of the HWRB and the reconstruction of the object field from such a hologram has been demonstrated by Van Heerden. The reconstruction is usually performed by a part of the field scattered by an object, by virtue of the HWRB selectivity. This selectivity amounts to definition of a useful signal against the background due to coherent addition of the image points and noise intensities. The associative properties of an HWRB, i.e., the reconstruction of the entire object field from its part, have been reported. However, such an associativity reduces to a minimum the advantages of HWRB since the reconstruction of the object field requires the actual presence of the object. Moreover, the illumination conditions must be identical to those during the recording of the hologram. We propose a somewhat different approach to the above associativity. To reconstruct a field, a set of reconstructing sources whose characteristics are the same as those of a set of object field sources is required. Such a reconstructing source is characterized by its coordinates, radiation phase, size, amplitude modulation, and polarization. These characteristics affect the object field reconstruction process differently. Thus, the polarization of a source has no effect on the signal-to-noise ratio, determining only the overall intensity of the reconstructed field. The amplitude modulation is also found to be insignificant for the reconstruction of a signal from a HWRB. This is evident from the experiment where the amplitude modulation is accomplished by means of a transparency placed in an immersion liquid. During the hologram reconstruction the amplitude transparency is replaced by another one. A drop in the phantom image intensity can be attributed to the fact that the original phase relationships could not be completely retained.

Laser doping method has an attractive set of important advantages, very useful for microelectronics applications. Using this method we have obtained shallow and heavily doped p⁺ - n junctions, ohmic contacts, and interconnection lines. We have extended our laser method for Ti in-diffusion into LiNbO₃, the common technique for optical waveguides fabrication.