The possibility of the effective induction of human platelet aggregation by CO₂-laser radiation has been experimentally stated. Radiation parameters required for the aggregation induction have been estimated. A mechanism of platelet activation influenced by radiation has been under discussion.

In this report there are the experimental results, which has been received with cell cultures and animals. We have found the photosensitized stimulation of the protective reactions of an organism, which has no direct connection with the photosensitization of the tumor cell destruction. It has been supposed that this photobiological process started from the photomodification of malignant cell membranes, its making strange cells for organism, and/or from the photomodification of the immunocompetent cells of the peripheral blood, increasing its cell killer activity. It has been shown that there are at least two competitive photoprocesses at use of monochromatic light. The first realizes the sensitized photodestruction of the malignant cells, and the second stimulates their reproduction. The latter decreases efficiency of PDT. It has found that the polychromatic (white) light suppressed processes of the malignant cell reproduction.

Involving high-power lasers into clinic medicine significantly extended the possibilities of the endoscopic surgery, which in a number of cases becomes a serious competitor to the traditional surgical methods of treatment14. Endoscopic surgery lowers the intervention risk, reduces the terms of patient's hospital treatment, the patient's activity can be restored in a shorter post-operational period and a possibility appears of carrying out complex operations in ambulance conditions. Endoscopic operations nowadays are made using mostly a continuous YAG: Nd laser with operating wavelength 1.06 1um. However, there exist serious restrictions on use of this type of radiation for the endoscopic surgical interventions at the gastrointestinal organs. They are connected with wall perforation risk .Endoscopicusing of a CO2 -laser, which works as an excellent scalpel in general surgery, is connected with technical difficulties of 1.06Mm radiation transmission by a flexible light guide. Moreover, the the hemostatic properties of this kind of radiation are rather limited. The specified above reasons stipulated that the practical medicine be interested in solid YAG-Cr-Tm: Ho lasers with wavelength range of 2,um and their application in the endoscopic surgery. Few published (including our own) results of biological investigations of biological experiments on the exploration of 2,um laser radiation affect at different tissues9 allow us to talk about the following. This radiation approaches to 10.6 1tim CO2 -laser radiation by its cutting effect to the soft tissues. However, its properties are opposite to the effect of volumetric coagulation which is inherent in 1.06 1um YAG: Nd laser radiation. It is known that protein compounds, pigmental components and blood ifiling extent have a smaller impact on the absorption of medium 1.5-3 1um JR wavelength range in biological tissues than absorption of visible and near JR radiation. For the increasing wavelength the impact of water on the absorption process is predominant. For the 1.06 ,um wavelength radiation the coefficient of radiation absorption in water is --0.6 cm whereas for wavelength 2.09 um it is'° '5O cmi. Theoretical estimation for the penetration depth of visible and JR laser radiation demonstrates that for 1.06 4um radiation it may reach 5-10 mm, and for 2 1tim radiation it is no more than 1-1.5 mm (Fig.1). That is, a significant (comparing with 1.06 1iim radiation) surface localization of secondary heat supply in tissue during its irradiation by 2 1um radiation takes place, therefore, a higher absolute temperature values as well as temperature gradient in the tissue irradiation epicenter appear. So, one can create conditions with equal energy input for a more intensive thermal destruction of tissues, accompanied by processes which determine the efficiency of tissue dissection: water vaporization, protein component sublimation and active removal of interaction products from the application zone.

An analysis of the technical problems involved indicates that the use of lasers in the vascular system remains a complex problem, but one that is eminently approachable with continued research. The emphasis should be on continued basic research rather than on the accumulation of large clinical experiences with less than adequate technology. There is great potential for the development of a percutaneous treatment for coronary artery disease that may reduce restenosis rates compared to those seen with percutaneous transluminal balloon angioplasty. Development of an effective percutaneous treatment of coronary artery disease with long term durability is critical to the advancement of interventional cardiology.

Physical mechanisms of ms laser lithotripsy in the visible range are discussed. Theoretical model for the case of stones which can be represented as a high-scattering low-absorption medium containing high-absorptive organic micropores is developed. The evolution of the state for such individual pore under the influence of laser radiation is described. Governing equations are derived and it was shown that there exists avalanche-like process of pore absorption increase due to the process of pyrocarbon generation. This generation is caused by the thermochemical dissociation of pore organic matter. Such effect leads to the increasing of laser pulse energy absorption and pressure front formation. This front may account for destruction of significant layer of the stone surface. Plasma can not flush under the conditions typical for described process. It starts to play a significant role only after primary stone destruction produced by proposed mechanism. Sharp increasing of stone absorption and modification of the destructed layer state may be considered as a good boost for the later effective plasma generation.

With the increasing use of both pulsed and CW lasers in the spectral region between 1100 nm and 3000 nm, biological research studies were performed in several laboratories to better define threshold effects. From this research both national committees (e.g., ANSI Z136 in the USA) and international committees (IEC TC76) have recommended increased occupational exposure limits (ELs) for lasers in this spectral region during the last year. Within the retinal hazard region, at wavelengths between 1200 and 1400 nm, ELs were increased by 8, and at wavelengths between 1400 nm and 2600 nm the ELs were raised as much as 100 times for short-pulse exposure, depending upon corneal penetration depth for each wavelength. The measuring aperture has also been modified so that some low-power optical-fiber diode laser sources are no longer considered potentially hazardous. Some of the research that led to these EL revisions also has implications for corneal refractive surgery.

This paper is devoted to the influence of the laser radiation with the wavelength 2.7 micrometers onto the hard tissues of the tooth, skin and mucous layer of the tongue of the experimental animals. The prospects are shown of such a radiation for the processing of the tooth substances, providing rather efficient, damage less and practically painless preparation of the deep caries, as well as ablation of soft tissues.

The attempts to treat conservatively the intraocular tumors saving the eye and its functions are made with increasing frequency. For this purpose photocoagulation, beta-application exposure, protonotherapy, diathermocoagulation and cryodestruction of the tumor are performed (Terentjeva, 1969; Ziangirova et a!., 1969; Brovkina et al., 1977, 1982; Brovkina, Zarubei, 1986; Volkov et aL, 1987; Orellana, McPherson, 1984; Char, Phillips, 1985; Tse, 1986; Gurretson et aL, 1988; Manschot, van Sink et a!., 1988). According to Bezrukov (1988) enucleation still remains the main approach (84%) to the uveal melanoma treatment in Russia. However, this procedure performed even at the early stage of the tumor growth is not absolutely reliable to prevent the tumor metastasis. According to the different authors the postenucleation mortality rate Within first 5 years accounts for 24-45% depending on the stage of disease and within 10 years - 65-80% (Steinberg, 1967; Kotelyansky, 1974; Manschot, van Peperzeel, 1980; Bacin ci a!., 1988; Saraux, Pelosse, 1988 et al.). Thus a search for new radical methods of the uveal melanoma treatment proves to be urgent. The application of lasers in the clinical practice has opened the new era in the treatment of the intraocular neoplasms. According to Terentjeva (1975) the clinical efficiency of this method accounts for 89.5% in tumors with protrusion up to 4.5 diopters. Therefore the most promising trend in the therapy of the eye tumors is the development of new methods that can be used to treat large lesions. With this in case the application of new laser sources and special modes of irradiation may significantly extend indications for conservative treatment.

Using methods of optoacoustic spectroscopy, we investigated generation of heat after absorption of light pulse in hemolyzed and intact blood. Differences due to absorptions distribution (homogeneous or in erythrocytes) were theorectically evaluated. Experimental values for whole blood were found to be noticeably lower then those theoretically predicted, strongly suggesting an existence of metastable states in cells responsible for storage of absorbed energy. Consideration of different ways for utilization of light's absorbed energy shows as the most probable hemoglobin conformational states and heat induced local deformations of cell membrane.

In order to investigate laser effects on biological specimens, Hydra, a coelenterate with high regeneration rate, was observed for ten days during regeneration after CO₂ laser cutting. Control animals were cut with a razor blade immediately below the tentacle whorl under a dissecting microscope while they were in small glass petri dishes. They regenerated tentacles completely 8 to 10 days from the cutting. Hydra were cut in the same position with CO₂ laser. As a first step, we studied the effect of the laser beam on the normal behaviour of hydra. For the cutting, we used four different power intensities: 0.5, 1.0, 1.5 and 2.0 W. At different power intensities the animals regenerated the tentacles. However in about 20% of the animals the amputation performed with 1 and 1.5 W originated a quicker regeneration of tentacles. No effect was observed on asexual reproduction of the polyps and therefore also no change of the bud index.

Many different types of proliferative retinopathy induced by various types of initial disorders have a common pathology in their mid and terminal stages. Thus, proper therapy is devoted toward elimination of the initial cause as well as alleviation of the proliferative processes. Vasodilatation, which is an initial symptom of diabetes, is itself destructive to the retinal capillary bed and appears to be a constant feature in all stages of diabetic retinopathy. In the mid and late stages, the vasodilatation seems very dependent upon capillary dropout, whereas the initial vasodilatation may derive from quite different causes. The efficacy of photocoagulation as a therapy for all stages seems to derive from decreasing the metabolism in the photoreceptor layer sufficiently to result in vasoconstriction of the retinal vessels. A model is proposed to show how diabetes, by altering the metabolism in the photoreceptor layer to produce excess lactic acid, causes the initial vasodilatation. The lactic acid also induces free radical (superoxide) formation; both act together to destroy the retinal capillary bed followed by vasoproliferation. Photocoagulation, thus, is even more appropriate for this particular syndrome than previously had been thought, as it not only reduces potentially destructive vasodilatation but also removes the metabolic cause of the free radical induced destruction of the capillary endothelium which is the initial step in capillary drop-out. A review of the present data indicates that the best type of pan- retinal photocoagulation is a very light type affecting the photoreceptors only with a minimal amount of damage to other parts of retina and the vessels in the choroid. The possible use of photochemical types of destruction of the photoreceptor as a therapeutic modality is attractive, but it is certainly too speculative to use until more detailed investigations have been completed. However, the basic therapeutic approach of choice may be to prevent the initial vascular involvement by preventing lactic acid buildup (or keeping the tissue pH normal) or by blocking the generation of superoxide with Allopurinol or similar medication.

The coagulative effect of the conventional CO₂ surgical laser at 10.6 micrometers is usually sufficient for homeostasis during surgery, but at laser wavelengths approaching 3 micrometers , the absorption depth is very shallow, and all the laser/tissue interaction is very close to the surface. Where ablation of surface tissues must be combined with a more penetrating laser action for coagulation or tissue bonding, auxiliary wavelengths are required. Significant penetration into the remaining unablated tissue is needed for coagulation of large blood vessels, as well as for generalized control of bleeding or seeping, or for more gentle, but even, heating of the cut surfaces of blood vessels, nerves, and other tissues as part of tissue anastomosis or bonding procedures. Also, large volumes of tissue are often removed as rapidly as possible; this needs deep penetration of the energy over a wide area. All of these effects call for wavelengths well away from the water absorption peak near 3 micrometers . Both ZrF₄ and sapphire optical fibers are sufficiently transparent in the visible and IR regions of the spectrum to pass an ablative wavelength near 3 micrometers , coagulative and tissue bonding wavelengths in the shorter IR, and another auxiliary beam in the visible to serve as a marker which will remain in precise optical alignment with the active and invisible IR beams. The control of the relative proportions of the various active wavelengths will allow selection of the precise surgical effect to be obtained, ranging from pure ablation to coagulation only or tissue bonding alone with all combinations in between. The concept of the multiwavelength laser delivery system will certainly be popular in the future whenever such instrumentation becomes sufficiently available for its utility to be widely recognized.

In laser cutting and welding processes time-unsteady phenomena dominate the fluid phases generated by high power laser interactions with workpiece material and assist gases. Violent reactive mixed fluid-flows with phase transitions must be understood and controlled to significantly improve current processing. An extensive experimental and phenomelogical analysis has shed some light on the events taking place and clarified some of the most puzzling aspects of the problems. New nozzle designs for the welding and cutting processes are proposed and have been proven promising in preliminary testing.

In order to control CO₂ laser surface treatments, a precise knowledge of the CO₂ radiation-surface coupling is required. For this purpose, numerical identification of the absorption coefficient, either with temporal resolution in non stationary 1D configuration or with spatial resolution in a stationary 2D configuration, were achieved from thermal cycles measurements and simulations. Evolutions of the coupling during laser treatment were studied both in the case of coated steel hardening (graphite and manganese phosphate coatings) and in the case of solid state nitridation of titanium alloys. Results were interpreted in terms of chemical evolutions of the surface; moreover, the influence of a reflective shielding gaz device covering the substrate was also pointed out.

Laser welding study under vacuum conditions was performed. Plasma parameters (particulary electronic density and temperature) were measured. They were correlated to the molten pool analysis, and give informations on the energy deposition process inside the keyhole.

The paper deals with dependence between the parameters of laser microprocessing system, used to scribe a microchannel on the floppy disk magnetic layer, and the parameters of the channel caused `missing pulse' information error, generated while reading the disk. The results are used to precise the laser microprocessing aimed at ensuring that both precise microchannel and information pulse.

Films of nanophase diamond can be prepared in vacuum by the laser ablation of graphite at intensities in excess of 10¹¹ W cm^-2. A variety of structural morphologies can result that depend upon the kinetic energies and charge states employed. The most promising is a nanophase diamond that we originally termed `amorphic diamond.' It is composed of nanometer scale nodules of sp³ bonded carbon. The high energy of condensation from the laser plasma source provides both for the chemical bonding of such films to a wide variety of substrates and for low values of residual compressive stress, 0.6 - 0.8 GPa. This paper reports the solution of a lingering problem with the hardness of nanophase diamond. The packing density of nodules in the finished ceramic depends upon process variables and so hardness can fluctuate. With critical control at the point of ablation, films are produced that are too hard to measure. In this work, raw data produced with an advanced nanoindentation technique was analyzed with the conventional procedure and a hardness value of 125 GPa was obtained. Exceeding the hardness of natural diamond this value was so large as to raise concern for the validity of the conventional model used to interpret data. To avoid model dependent interpretation, a differential loading pressure, independent of depth, was used to give a lower limit on the hardness directly from the raw data. Comparable values of this lower limit, near 75 GPa have been measured on crystalline diamond prepared by CVD and on nanophase diamond deposited by our laser plasma method. The combination of hardness and resiliency together with a coefficient of friction near 0.1, seems to make nanophase diamond an attractive coating for use in current industrial applications.

Two high power mid-IR gas lasers, the CO laser and the chemical HF laser, can offer higher absorption for metals and better focusing, i.e. smaller spot areas than CO₂ and Nd:YAG lasers. A comparison of the effects of three gas lasers is carried out at the ISL, using three high-power gas lasers: 1 kW (HF), 6 kW (CO) and 7.5 kW (CO₂) and allows to compare their effects on different materials. The absorptivity of these laser beams for several metals has been measured, both with low energy measurement techniques and with high power laser beams; an increase in absorptivity has been demonstrated for the short wavelengths lasers. Plexiglass irradiated with these lasers beams exhibits a boiling-type destruction behavior. The threshold fluence for the occurrence of the bubbles has been measured and compared with a simple boiling model showing the importance of the spectral absorption coefficient.

An effective procedure for nonlinear spectroscopy of high-T_c superconductive thin films is proposed. It enables to determine as their phase, as critical temperature, superconducting energy gap width, constants of interaction, etc. Results of its testing for Y-Ba-Cu-O thin films are presented, including results of investigation of relaxation kinetics of preliminary picosecond optical excitation.

We present and discuss a technique to measure concurrently the temperature dependence of quartz refractive indices in the thermal range 25 degree(s)C - 300 degree(s)C. The magnitude of both indices is found to decrease slightly with increasing temperature in the thermal range considered.

Analyzed are different measurement methods of high quality optical cavity characteristics based on the many-beams interferometry effects. The discussion of the opportunity to make coefficients of total and diffraction cavity loss measurements, reflectivity measurements of low-loss highly reflecting mirror coatings and gain measurements of the active substance is given. The possibility to control of the resonance cavity spectrum, a level of selection, a quality of the mirrors alignment and an accuracy of the cavity monoblock making is discussed. Compared is the method based on the analysis of the cavity transmission spectrum and an alternative method based on the exponential decay time measurement. It is shown that examined methods are suitable for high quality cavity loss measurements although each of them has own peculiarity and own primary sphere of application. Each of them may be more or less of use for others enumerated laser parameters measurements.

In the paper the test results of the device with selfcorrection of basic gyro errors are given. Low sensitivity of angle orientation measurement errors to such gyro errors as instability of zero shift, its drift and scale factor is shown. Experimentally shown that orientation error about each of three axes is about 5% of gyro drift and more depends on variation frequency of measured angle speed than gyro errors. Proposed design scheme of the device is expedient to use for the development of navigation systems employing not only small-sized laser, but fiber- optic and integrated optic gyros.

Remote investigations of natural objects by optical means forn a set of inverse problems comprising the determination of medium proper— ties and their distribution over a source—receiver path, on the one hand, and coordinates and parameters of sources, on the other hand, by characteristics of scattered radiation. During such studies, more and more attention is paid to analyzing the polarizatioa-ternporal pattern of the radiation field scattered by atmosphere1 . This interest is due to polarized radiation as coanpared with unpolarized one con— tains much more information on physicocheinical and structural proper— ties of objects studied. While conducting atmospheric optical investigations, polarization rneasureaients can be used, for example, for inde— pendent estimation of atmosphere turbidity and its transparency, for detection and studying the turbid zones at different directions from an observer, determination of earth' albedo, isolation of aerosol coin— ponents, separation of the atmospheric absorption and scattering, lo— cation of o tical sources, and calculation of their parameters. Taking the intensity alone into account without reference to polarization does not simplify the analysis, but also can lead to incorrect results. Each of the possible aforementioned applications is based on empineal relations required not only to be verified and confirmed, but also upgraded by means of mathematical statistical methods relied upon more full sets of polarimetric observations in real atmosphere. The computer—controlled iaeasuring system for analyzing polarization (MSAP) made at the Institute of ?hysics, Academy of Sciences of Belarus is described below to be designed for studying the polarization characteristics of optical radiation scattered by atmosphere and of radiowaves accompanying the latter. This system has been used for field atmospheric investigations including that under ocean conditions

The simple technical realization of the homodyne method for the atmosphere turbulence parameter measuring is suggested. Theoretical model of the method and various approximations are analyzed. Special attention is paid to the reliability of the results and to the equipment characteristics, distorting the measured values.

The potentials of laser-induced microwave photoconductivity (LMP) as a diagnostic method for semiconductor surface studies are considered in this paper. The principals and practical realization aspects including a block-diagram and technical characteristics of the LMP apparatus, and some experimental data on electron-recombination properties of Si and GaAs surfaces are presented. The data include investigation of non equilibrium carrier relaxation channels and rates, influence of various defects (traps, adhesion centers, dislocations etc.), and spatial variations of these relaxation characteristics in surface layers modified with different procedures (ion implantation, laser annealing, mechanical treatment). Among the remote action of surface modification and interaction of locally modified zones. These effects are shown to be very important in the physics and technology of semiconductor surface modification. It is concluded that the LMP method is very informative diagnostic tool for testing and studying of semiconductor surfaces and device structures used in microelectronics, power electronics and optoelectronics.

The wake of a ship is a region of highly turbulent flow. The wake characteristics are dependent on hull shape and propeller performance. In order to progress hull deign and maximize vessel performance detailed measurements of the flow are required in this difficult region. The present paper describes experiments in which PIV measurements of the turbulent flow in the wake of a model ship were made using a pulsed Nd:YAG laser illumination system which was computer controlled. The experiments were conducted in a 25 m towing tank with a 1:97 model destroyer. The laser beam entered the tank via a periscope. Observations were made using a second periscope viewing arrangement. During the experiment the YAG laser was fully controlled by computer to optimize the output and to control the distribution of energy between pulses. The camera operation was also controlled by computer. A description is given of the experimental arrangements including the control system used with the laser. The optical viewing arrangements are described as is the method of image analysis used. Example velocity measurements are presented.

Three different techniques for signal amplification utilizing, cavity resonances are examined. Cavity-enhanced photothermal spectroscopy and cavity-enhanced photovaporization spectroscopy are based on resonator optical cavities and cavity-enhanced capillary wave spectroscopy is based on a mechanical resonator. The signal amplification can make feasible the measurement of small effects which would otherwise be obscured by noise.

We describe frequency stabilization of two laser-diode-pumped Nd:YAG lasers independently locked to two high-finesse Fabry-Perot cavities. The frequency noise is reduced to the shot noise limit of 0.37 mHz/(root)Hz at the error signal. A heterodyne beat note between two locked lasers is used to measure the frequency stability, and the beat linewidth of 16 Hz and the root Allan variance of 19 Hz at time interval of 3 ms are measured. A new scalable geometry of multi-LD-pumping for high power and TEM₀₀ output solid state lasers have been developed. The principle of virtual point source clad pumping system is discussed in terms of analytical and numerical calculations. A prototype model was developed by using 32 X 1 W - fiber-coupled LD. The center core of 200 micrometers diameter of 2-mm YAG rod was excited efficiently. The transverse mode of output was controlled simply by changing the ratio of excitation volume to cavity mode volume. The high power version of 320 W pumping is designed and appear in the near future.

Stimulated resonant Raman (SRR) processes have beai widely used for high precision spectroscopy of atoms and molecules [1], especially when the levels of interest are metastable. Owing to the long lifetime of these levels, one may obtain extremely narrow SRR resonances which are useful both for spectroscopic and metrological applications [2]. There is a close analogy between the SRR interactioo of the three-level systn with two laser beams at frequencies vi ,V2 , and the interaction of the two ground level hyperfine states with a microwave radiatii at the frequency (v1 -v2). Because of this analogy, our experiment has soiue commoo features with that of optical miaowave double resonance [3], but it provides a better signal-to-noise ratio and a simpler experimental set-up. The present paper illusirales how useful SRR spectroscopy can be for the study of hyperfine sucture of the ground electrouic state of 12. We have indeed observed SRR transitions between hyperfine sublevels of the ground elecnothc state x1: ÷ (v=O,J= 13) of 2 flffOWf than 10 kHz (HWHM) have been obtained. We have measured Og six byperfine transitions with a 0.2 kHz accuracy. A pressure broadening of the SRR transitions equal to 7 1 kHzimtorr has been found. A third-order calculation of the line shape based on the diagrammatic representation of the density matrix equations is presented. The experimental line shapes of the SRR resonances are in good qualitative agreement with the results of the calculation. The advantages of this method for higb precision spectroscopy of iodine are thwusse .

Phase modulation interferometer with the phase difference computed from the ratio of the first and second harmonics amplitudes has been developed. Signal distortions and deviations of measuring conditions against normal conditions are analyzed and appropriate corrections are made. The instrumental error of small displacement measurements is equal to +/- 0.8 nm (0.95). The digital readout interval is of 1 nm.

Analysis of comparatively low-threshold interaction of laser radiation in vacuum is given. Efficiency of mixing of three waves with frequencies (omega) ₁, (omega) ₂, and (omega) ₃ resulting in generation of combination mode with frequency (omega) ₁ + (omega) ₂ - (omega) ₃ is studied. The possibility for demonstration of vacuum polarization phenomena in laser experiments is shown.

The generation of nonclassical states of light in optical fibers with a spatial beating of the energy for traveling modes is considered. The effects of quantum squeezing and correlation of photons for two types of optical fibers, i.e. for tunnelly-coupled (dual-core) and for spatially nonhomogeneous fibers, are studied. It is shown that in the field of ordinary CW He-Ne laser at intensity of 100 W/cm² the suppression of quantum (vacuum) fluctuations of one of the field quadrature components may obtain of a value about ten percent. The possibilities of experimental realization both of suggested scheme for the squeezed states generation and of carrying out of quantum non-demolition measurement are discussed.

Quality factor 2.5 X 10⁹ at the wavelength (lambda) equals 0.63 micrometers is reported in approximately 100 micrometers spherical resonators of fused silica with whispering-gallery modes (equivalent finesse F equals 2.5 X 10⁶). Quality-factor 3 X 10⁷ and effective thermal tunability of modes (up to 0.1%) is demonstrated in whispering-gallery microresonators of optical glass. Dispersive bistability and other nonlinear effects are observed at the level of input power about tens of microwatts. Nonlinear properties of optical whispering-gallery modes are investigated by mode cross-modulation technique. Prospects of applications in linear signal processing and quantum-nondemolition measurements are outlined.

The paper classifies the requirements to initial soliton-in-fiber deriving optical pulses. The active mode-locking regime in semiconductor lasers with an external fiber cavity is considered from a position of soliton technique. The additive active mode-locking regime in semiconductor laser is proposed and analyzed. This new regime is used for the generation of multibit binary words, which are suitable for soliton transmission through a long-haul fiber.

The propagation of cw laser beams oppositely travelling in a polymeric blend (PMMA-EVA) is analyzed in order to study the thermo-optical behavior of such a material. The experimental results show optical bistability due to the mutual self-action of counterpropagating beams. The thermal coefficient of the refractive index dn/dt of PMMA-EVA is calculated by a simple theoretical model. This value is in well agreement with that one obtained by us using an interferometric method.

We present results of experiments on generation of optical harmonics and sum-frequency radiation in a low-temperature laser-produced plasma. A plasma of optical breakdown is shown to be a prospective nonlinear medium for producing coherent short-wavelength radiation via harmonic generation and frequency mixing. We discuss experimental data on generation of third, fifth, seventh, and ninth harmonics of Nd:YAG-laser radiation, as well as processes of nonlinear frequency mixing.

We present the results of computer simulations of laser diffractive autosolitons--particle-like field structures in the wide-aperture lasers with saturable absorber. Existence of transversely motionless and moving patterns in one- and two-dimensional laser schemes is demonstrated.

The linear problem of p-polarized laser radiation absorption in sharp-edged plasmas under the normal skin-effect regime was considered. Magnetic component equation has been solved analytically by the use of perturbation techniques in the limit when the density scale length is much less than the laser wavelength. Asymptotic expressions for an absorption efficiency have been obtained for a linear plasma density profile.

In a bulk Kerr material, no analytical solution is known to yield stable soliton beam propagation. The most frequent experimental situation leads to a well-known chaotic beam break-up into numerous randomly distributed self-focused spots. An interferometric method is proposed to achieve a 1D phase-matching of the self-focused spots through a Kerr-induced index grating. By this way, self-splitting of the laser beam into multiple solitons occurs in bulk CS₂. When the material exhibits stimulated scattering in the picosecond or nanosecond range, the present method yields also to a distributed feedback that gives rise to Raman or Brillouin soliton-like beams.

A non-stationary reflection of continuous wave beam from a Kerr layer at a small incident angle is proposed based on numerical simulation. The angle of laser beam propagation and it center have a temporal oscillations near the average value at the end of nonlinear layer.

New approach for modeling of multimode dynamics has been developed for real cavity conditions and approximation of thin active media. The rigorous mathematical procedure of local singularity description is proposed.

In recent experiments we have observed the predicted mutual deflection of two circularly polarized laser beams intersecting at a small angle. In a similar experimental setup but with entirely superimposed beams at the entrance of a Sodium vapor cell, a spatial instability of the propagating laser beams within the cell occurs which leads to a sudden transverse `splitting' of the input beams into beams of pure circular polarization. We compare the experimental results to the predictions obtained from a theoretical approach based on the modal decomposition of the coherent fields.

The nonlinear problem of speckle-beam propagation in the photo-refractive crystals has been solved. The solutions corresponding to the beam trajectory self-bending have been obtained both in approximation of infinite beam diameter and for the case of finite one. The local tilting rate of the beam propagation direction proved to be proportional to the square of beam angular divergence. The influence of space-charge limit field on the trajectory curvature radius has been investigated as well.

Recording and reconstruction of pico- and nanosecond pulses were accomplished with spectral holography. The developing of spectral holography in nanosecond time-domain was provided while using high-spectral-resolution equipment based on Fabry-Perot etalon with the side entrance/exit. The recognition of shaped nanosecond light pulses was also realized.

The results of the holographic recording and reconstruction of the time-domain profile of femtosecond laser pulses in the polymer volume medium named Reoxan are presented. The experimental data show the possibility of the effective spectral filtering to control the shape of ultrashort pulses.

Resent progress on multishot laser damage ofwide-gap optical materials is linked with the idea of gradual or explosive accumulation ofpoint defects accompanied by some structural changes in a material (see Reviews [1,21). According to the quantitatively developed model of ReL[2J the F-center accumulation proceeds in explosive manner due to the decrease of the defect formation energy by selfconsistent medium stress. Multiphoton free carrier generation across the forbidden band gap and subsequent rapid cascade defect reactions, involving excited electrons and holes and leading eventually to F-center formation are other essential features of the model of multishot laser damage developed in this approach. According to Ref[2J these reactions occur in the following manner. Intensive laser light with quantum ofenergy two(Eg iflthXS multiphoton electron transitions into conduction band of a dielectric. Autolocalization of a free hole at some crystal site creates Vk -center, which then captures free electron with formation of a self-trapped exiton (STh). Recombination of autolocalized electron-hole pair leads to the STE decay accompanied by liberation of an energy sufficient for production of F-center (vacancy) and H-center (interstitial) in adjacent crystal sites. The cascade of above reactions with recombination4nduced vacancy production is completed by time scale of 1O_12 ÷ 10" s [3]. The generation of interstitials, accompaning F-center production, leads to the local expansion of crystal lattice [11,12], which decreases the F-center formation energy. The arising positive feedback leads to explosive F-center generation that may be considered as an absolute defect concentration instability developing locally. When the dilatative stress due to generated interstitials reaches the value of yield stress of a material then the damage threshold is supposed to be reached [2]. The model dependencies of the number of shots, leading to damage, on the photon flux in a laser pulse at different initial temperatures was shown to correspond well to experimental ones [2]. The model ofRef.[2] is relied implicitly on the assumption that the localization of a free carriers leading to a Vk -center and a STE formation occurs at regular crystal sites with the same rate as at defected ones. In this case the spatial distribution ofthe generated defects follows the laser intensity distribution in focal region. In this work we study another opportunity and assume that the rate of free carriers localization at defected sites is much bigger than at the regular sites (which at least in semiconductors certainly is the case [5]). We show that in this case one comes to the model ofexplosive F-center formation and resulting damage essentially differed from that of Ref. [2]. The physical essence of the proposed model consists in the following [6]. We assume the same cascade of reactions as in Ref.[2] to be responsible for F-centers (vacancies) production in a laser excited medium. We exploit the assumption that the above cascade reaction with defect production occurs much more rapidly near defected sites. Thus the above cascade reactions are initiated at initially present defects that leads to appearance of strain in their vicinity which decreases locally the defect formation energy. This leads to further enhancing of defect generation and appearance of strain. This defect generation-strain appearance cycle is repeated again and again in vicinity of newly formed centers, leading thus to defect formation wave (DFW) propagation in laser excited medium [6]. Thus instead of local (absolute) defect generation instability of Ref.[2] we develop here the model of distributed (convective) defect generation instability. We note that the strain induced positive feedback and corresponding vacancy generation-deformational instability (ODD developing in condition oflaser irradiation in strongly absorbintg metals and semiconductors was considered earlier in Ref.[7] and is shown to lead to formation of ordered defect structures (for review of GDI see Ref.[4]). The DFW model also takes into account the long range character of the medium deformation, which is shown here to lead to strain induced DFW propagation with steady velocity. The passage of this DFW switches the medium from the state with zero defect concentration (n= 0)to the F-center enriched state with F = X . Ifthe value of n exceeds the Critical defect concentration 4 iO' cni at which deformationinduced extended defects (voids) nucleation begins [4] then the switching wave ofpoint defect production is accompanied by switching wave of extended defect nucleation i.e. by mateiial damage. This work is dedicated to studies of the model of switching wave ofpoint defect generation. proposed in [6J. We apply the theoretical results obtained to the problem of multishot laser damage in transparent dielectrics. The present model is shown to be in a good agreement with the expeiimental results on dependency of the number of shots leading to damage on the photon flux in a laser pulse.

The theoretical results have been compared with experiments carried out on laser plasma source. A significant role of the tail of the asymmetric subnanosecond pulse, that change noticeably the charge composition, was shown.

In recent years new high-intensity subpicosecond lasers allowed to investigate property of matter in ultrahigh electromagnetic fields. In this work the electron motion equations in field of three orthogonal standing waves is being solved. This solution was obtained by method of average Hamiltonian, when the electron velocity in laser field v_E equals eE₀/m(omega) is less than light velocity c ((omega) - laser frequency).

Quasistationary fields generation at high-power laser pulse propagation in rarefield plasma is considered. Circularly polarized pulse propagation is shown to be accompanied by low- frequency electromagnetic field radiation. The field structure and energy losses associated with pulse radiative deceleration are determined. The comparison is made of quasistatic electromagnetic fields magnitudes with wake electrostatic field.

The basic equations are formulated to study the selfconsistent space-time evolution of a intense ultrashort laser pulse and near-backward stimulated Raman scattered radiation. The analytic theory and numerical results are presented for spectra and intensities of scattered radiation produced by a laser pulse with a given form. A simple criterion is found for the weak influence of stimulated Raman backscattering (SRBS) on a pulse propagation. A few results of numerical simulations, showing the temporal evolution of SRBS spectrum by laser pulse propagation, are presented.

We regard the amplification of Stokes pulses with diffractional divergence for stimulated Brillouin scattering compression in multimode pump irradiation. It is demonstrated the possibility of effective compression up to nanosecond duration with conservation diffractional quality Stokes pulses or anti-phase conjugation, into pump range from tens up hundreds jouls which is comprehensible for experimental testing.

Possibility of recording second-order nonlinear susceptibility in commercial specially synthesized lead-silicate glasses was investigated. Photoinduced SHG in glasses with lead content from 10 to 40 mol% was found effective. Optical waveguides by ion-exchange were made in these glasses.

The results of theoretical and experimental studies carried out by the author on non-linear parameter transformation of light signals by a photorefractive effect in crystals are presented. The following items are considered: results of photoinduced variations of the natural eigenwaves refraction index and their polarization; formation processes of photo-charges stipulating the recording of polarizing--phase gratings due to longitudinal and transverse electrooptical effects; the operative transformation means of spatial-temporal characteristics of coherent beams; investigation results of non-stationary response providing the transformation of light beams carrying complex information in the time evolution process. Thus the main attention is focused on establishing a non-linear relationship between spatial properties of the photo-active light intensity in the image being recorded and optical anisotropy arising under the photo-charge effect.

The present work is concerned with the reflection and transmission properties of electromagnetic waves from finely divided fractal layers. We develop an exact iterative algorithm that provides the reflection and transmission coefficients for a multilayers stack made of two and different homogeneous materials constructed according to the pattern of a Cantor fractal set.

Light induced changes of optical properties are in close relation with photoelectrical properties of semiconductors. From the dynamics of nonlinear optical response, not only electronic parameters of crystals but also the channels of energy relaxation, role of defects and mechanisms of light interaction with matter may be studied. Light diffraction on laser induced transient gratings has proved to be a very powerful technique for these fundamental swdies of semiconductors as well as for their applications in opto- and microelectronics. Photorefractive Ill-V and il-VI semiconducting compounds reveal optical nonlinearities of different origins under excitation by short las pulses or by CW lasers [1,2]. The contributions to refractive index modulation by free carriers and by space charge electric fields coexist at pulse excitation while solely linear electrooptic effect is responsible for optical gain in a quasi-stationary case of excitation. Carrier plasma kinetic coefficients, as ambipolar and monopolar mobiities, carrier concentrations and lifetimes, defect concentration and other parameters may be obtained from light diffraction on transient grating experiments [3-7]. In addition, at short pulse excitation a number of novel effects have been obsved: light induced space-charge (SC) field enhancement [8], fast oscillations of diffraction efficiency and multiexponential grating decay [9,10]. These effects probably arise from simultaneous presence of two refractive index modulation mechanisms and their interaction. Indeed, the diffusive decay of free carrier grating leads to the build-up of space charge electric fields, which in turn involve electron and hole sal separation, screening of space charge fields, and affect the decay processes of electronic gratings. A significant step towards the understanding of the temporal behavior of nonlinearities involved as well as possibilities of those optical techniques for semiconductor research may be obtained by help of a detail analysis of carrier and field dynamics in different experimental situations.