Method of analysis of self-action of intense light pulses of several light wave oscillations in dielectrics is proposed. The system of material equations based on the density matrix formalism allowing for both the electronic and electronic-vibrational (Raman) nonlinearity is obtained. The results of the numerical experiments on the self-action of extremely short light pulses in fused silica is presented.

A class of new nonlinear effects in the interaction of the electromagnetic field with a medium is revealed: the existence of ''half-wave'' electromagnetic field solutions in a passive nonlinear medium, and formation of nonstationary wave packets whose frequency increases as they are amplified in an active medium.

The wave equation has been solved in the first approximation to investigate the process of self- diffraction of ultrashort light pulses in a nonlinear medium. A new theoretical method for the analysis of the behavior of ultrashort pulses in a nonlinear medium is proposed. Comparison of the new method and the slowly varying amplitudes method is made. The two methods are shown to be identical for long pulses, whereas in the case of ultrashort pulses the slowly varying amplitudes method leads to incorrect results.

Pulse self-phase modulation has been calculated analytically and by means of computer simulations for both focused and unfocused beams. It is shown that when a strong nonlinearity exists, the characteristic feature of spectrum is an intensive peak at the laser wavelength.

Investigation of nonlinear pulse propagation is nonuniform or periodic structures are the subject of current interest due to the wide range of opportunities for controlling the group- velocity dispersion of these structures. In this paper, the dynamics of the optical solitons in a single-mode fiber with modulated core radius with a period comparable with the dispersion length are treated numerically. This modulation may be easily achieved in fiber production.

Generation of ultrashort pulses in an actively mode-locked fiber laser are investigated analytically and numerically. Utilization of soliton pulse shaping makes it possible to shorten the output pulse width by more than one order of magnitude without loss of average power.

The existence of a specific wave object that arises when a spatially limited electromagnetic wave with abrupt leading edge propagates in vacuum is predicted. This object demonstrates a precursor-like behavior, since the diffractive spreading of the field proceeds behind it. The transverse structure and the field strength at the leading edge of the object remain unchanged during propagation, whereas its energy decreases as z-1 due to diffractive erosion of its trailing edge. This phenomenon to a certain extent resembles the Sommerfeld precursor formation in temporally dispersive medium.

Experimental study of stimulated diffusion backscattering in photorefractive crystals demonstrates that the phase conjugate component grows faster than other components of the scattered field in the case of pump radiation with a moving speckle structure.

A possibility of a formation of holographic gratings with non-overlapping electromagnetic pulses is demonstrated. The coherent erosion by a single pulse should be relatively low to permit an efficient hologram formation.

Most photorefractive crystals, suitable for the realization of self-pumped four-wave mixing phase conjugation and mutual conjugation geometries, are characterized by the high level of fanning. In some cases it may mean that the nonlinearity of these crystals is already too large to be good and a decrease in the value of a nonlinear coupling coefficient may result in an improved performance of these geometries. This point is illustrated using geometry of a self- pumped ring mirror.

Steady emission of a phase conjugated beam from a photorefractive BaTiO₃ crystal is generally obtained via a self-pumping process when the four-wave mixing configuration emerges in the crystal, provided the two intense beams generated by an input beam travel, after the reflection from the corner of the crystal, along each other's path in opposite directions. However, sometimes many intense beams originate from the input beam and, after the reflection from the corner of the crystal, make several four-wave mixing configurations to produce a stable phase-conjugated beam. When the diameter of the input beam does not exceed 20 micrometers , the intensity profile of the phase conjugated beam is quite different from that of the input beam. The difference is a dark spot in the former beam. The size, location, and shape of the hole differ drastically depending on the input beam incidence angle and relative position of the input beam waist and the crystal center. The differences in the internal beam configuration in the BaTiO₃ crystal for each phase conjugated are not as distinct as the differences in their pattern.

High degrees of linear polarization of laser radiation and sensitivity to its variation are achieved by applying frequency converters using nonlinear crystals as polarizers and analyzers. The factors leading to distortion of linear polarization of light in such devices are identified. A KD^*P polarimeter with extinction ratio of 5 (DOT) 10^-9 is developed on the basis of a quasi-CW picosecond YAG laser.

Theoretical investigations of the stability of steady-state field patterns with respect to arbitrarily polarized plane perturbations demonstrates that the bi- and multistability, as well as near self-oscillation processes, exist in the two-pass optical system containing nonlinear isotropic medium and a rotating mirror.

In the present paper the polarization self-action of light in arbitrary oriented cubic crystals of 432, 43 m and m3m groups are considered. The equations of evolution of light polarization parameters in this case are derived. The detailed analysis of SICP effects under the propagation of light wave along the all symmetry axes is presented. The eigenpolarization of light wave in nonlinear crystal are found. The dependence of nonlinear effects caused by SICP (self-induced rotation of self-induced deformation of polarization ellipse, self-induced oscillation of polarization ellipse or establishing of stationary state of polarization) on orientation of crystal's axes with respect to wave vector, nature of nonlinearity of refractive index (relations between components of nonlinear susceptibility tensor) and input state of light polarization is determined.

Absorption of laser radiation leads to the birefringence zero crossing shift in gyrotropic isoindex crystals. Thermal nonlinearity is responsible for the effect. Possible applications for light-by-light control devices are discussed.

The peculiarities of the light transmission nonlinear charge were studied in the case of interband excitation of the chalcogenide glass thin films by nanosecond and picosecond light pulses. The transmission optical hysteresis due to photoinduced absorption is registered. The nonlinear behavior of the thin chalcogenide plates acting as a Fabry-Perot cavity is investigated in picosecond time scale. The possible explanation of the revealed nonlinearities is proposed.

The nonlinear absorption in LiNbO₃:Mg crystals exposed to pulsed green laser radiation was studied. A brown track in LiNbO₃:Mg was observed at room temperature. A dose of green light about 2 J/cm² was necessary to reach the maximum coloration, the corresponding absorption being proportional to the square of optical power density. This absorption adds to the two-photon absorption thus increasing the total nonlinear absorption approximately by a factor of eight. The coloration can be bleached by heating (the relaxation time constant being less than a second at 100 degree(s)C) and by exposure to the visible light with small peak power density. The nonlinear absorption limits the efficiency of second harmonic generation (SHG) at room temperature. A 40 to 50% efficiency rise accompanying the temperature increase was caused by the decay of coloration. The two-photon pumping of electron traps is a plausible trigger mechanism for laser-induced coloration.

Transmission spectra recovery and time-resolved luminescence of CdSe microcrystals optically excited by ultrashort laser pulses have been studied with picosecond time resolution. The transitions between levels of electrons and holes spatially confined within microcrystals were observed as bleaching bands in nonlinear transmission spectra. The significant shortening of the carrier lifetime in microcrystals of smaller size was detected. The regime of laser emission at the transition between the lowest levels of size quantization was achieved.

The peculiarities of a higher harmonics photorefractive response are considered theoretically for a grating recorded through a mechanism of phase-locked detection by external ac field. The conditions of existence of a higher harmonic grating are found analytically.

The problem of stability of excited frequencies is considered for a ring doubly-resonant optical parametric oscillator. The theory developed is based on the fixed field approximation used to analyze the interaction of waves on the tip of resonator cavity. It is shown that the excited frequency fluctuations arising due to resonator parameter variations can be largely suppressed. The suppression coefficient of technical fluctuations can be equal to 10³ and more.

The novel microscopic mechanism of threshold efficient second harmonic generation in centrosymmetric solids is proposed.

The investigation of spatial spectra, dynamics, and statistics of parametric holographic scattering in photorefractive LiNbO₃:Me (Me equals Fe, Cu, Ti, Mg, Zn, Nd, Sn) crystals is reported.

The responses of an all-optical bistable system and an analog model of the Brownian motion in the symmetric Duffing potential to a weak periodic force in the presence of noise are investigated. The appearance of a stochastic resonance in both cases is explained in the theory of a linear response.

Characteristics of stimulated scattering and parametric amplification of light are investigated in the case of nonmonochromatic pumping on the basis of exact analytical solution of some problems. Part I provides a review of publications devoted to stimulated Raman scattering (SRS). Some new results related to backward SRS are presented as well as the theory of SRS in the pump field of random telegraph signal type. Results of theoretical calculations are compared with the existing experimental data.

This paper presents a theory for parametric amplification of light in the case of non- monochromatic pumping. A possibility of conversion of the optical noise into a quasiharmonic signal as a result of Raman scattering in a selective resonator is discussed for the first time.

Phase conjugation (PC) of XeCl laser radiation using two different kinds of stimulated scattering, i.e., stimulated temperature scattering (STS) and stimulated Brillouin scattering (SBS), is investigated. It is shown that STS can be stimulated both by the linear and multiphoton absorption, and that SBS can be suppressed by the effect of phase-matching violation caused by the multiphoton absorption. The quality of PC deteriorates when SBS is replaced by STS. The two possible reasons for this deterioration are discussed.

The results are given of the latest experiments on optimization of self-PC of approximately equals 10 micrometers laser radiation by four-wave mixing in liquids. This paper reports the first realization of STS of pulsed CO₂ laser radiation in SF₆-Xe mixture. Possibilities are analyzed for the development of adaptive laser systems in the middle IR region for detection and amplification with PC of extremely weak optical signals (<EQ 10^-15 J) on the basis of FWM and FWMF mirrors available.

The experimental demonstration of phase conjugation technique as applied to aberration correction in a high-power gas-flow CO₂ laser is reported. A four-wave mixing in ³⁴SF₆ was used to obtain high efficient phase conjugation of repetition rate electron- beam-sustained CO₂ laser radiation. For the first time, the nearly diffraction-limited performance of the double-pass CO₂ amplifier with the phase-conjugate mirror for the output energy of about 1.2 KJ and average power of 40 KW is demonstrated.

A simple and efficient energy scalable technique of frequency conversion in Raman Stokes and anti-Stokes (AS) radiation with near-diffraction limited (DL) divergency is demonstrated. In AS beam energy and intensity, conversion efficiencies of 12% and 20%, respectively were reached, and up to 40% predicted. Six percent power efficiency of long pulse AS Raman parametric generator operation was achieved and up to 35% predicted. An efficient near-DL beam quality 14-color convertor covering all visible region was created.

Output control of the XeCl- and KrCl-lasers is summarized. Output energy, pulse duration, beam divergence, and linewidth characteristics are investigated. The results of SRS conversion of the XeCl- and KrCl-lasers radiation in hydrogen gas and lead vapor are presented.