The dynamics of atomic ionization by strong and superstrong laser field is now under intensive experimental and theoretical study [1-5]. In the present paper we develop the method, initially suggested in [4], by which we attempt to solve non-relativistic problem of ionization of single hydrogen like atom exposed to sub-, atomic and superatomic impact laser field from the ground state. Within the framework of this method we investigated matrix element of the ionization transition and revealed its substantially nonlinear dependence on the laser field amplitude. This allowed us to find new selection rules, which differ from that in dipole, quadruple or any other approximation of finite multipolarity. We are interested here in the above threshold ionization (ATI), therefore it is assumed that the atomic spectrum consists of the ground state and continuous spectrum. Both ionization and recombination processes are taken into account. The proposed method enables us to account for the ionization processes ofthe arbitrary order. The population ofthe states of the quasi-energy spectrum as a function of the laser field amplitude is investigated. The obtained dependency of the average ionization rate on the laser field amplitude is compared with the Keldysh formula.

The spectrum of the luminescence in the far wing of the atomic spectral line due to the atom-surface collisions between cesium atoms and sapphire surface is obtained experimentally. A cw diode laser operating at the wavelength of 852.1 nm resonant to the 6S_1/2 - 6P_3/2 transition in the free Cs atoms was used to excite the luminescence of atomic vapors. To avoid atom-atom collisions a specially designed spectroscopic cell with two sapphire windows only 3 μm apart was employed. The wings were measured for the detuning up to 200 cm^-1 on both sides ofthe atomic spectral line. Besides the wings, luminescence at the wavelength of 894.3 nm corresponding to the 6S_1/2 - 6P_1/2 transition was observed. Notwithstanding high quenching probability, more than 0.5% of the atoms leave the surface in the state of another fine-structure component.

Second-harmonic generation (SHG) is studied in semiconductors GaAs and CdTe in broad spectral and temperature ranges. External magnetic field gives rise to time-reversal symmetry breaking causing new optical nonlinearities. A series of narrow SHG lines is observed in the spectral range near the band gap of semiconductors GaAs and CdTe in nonzero magnetic fields. It is found that optical transitions between Landau levels are responsible for observed SHG spectra. The rotational anisotropy of the SHG signal distinctly differs from that of the electric-dipole approximation. Model calculations, based on phenomenological analysis using nonlocal contributions in the nonlinear optical susceptibility, have revealed an importance of the nonlinear magneto-optical spatial-dispersion that comes together with the electric-dipole term.

Electromagnetically induced absorption (EIA) in Hanle configuration versus ellipticity of an optical running wave is investigated. All theoretical results are confirmed experimentally quite well. It is shown that magneto-optical resonance parameters (amplitude, width and amplitude-to-width ratio) depend on the wave polarization substantially. For example, the rsonance amplitude in the case of elliptic polarization of th elight wave can be the order more than for linear polarization.

Based on the group theoretical analysis of the nonlinear electric susceptibility second harmonic response in different magnetic states of multiferroic bismuth ferrite is considered. It is shown that nonlinear magneto-optic effect can serve as an effective tool for spin cycloid structure detection in bulk material and probing homogenous antiferromagnetic state in thin films of bismuth ferrite. The study of antiferromagnetic state that determines magnetoelectric properties of the material is important in the context of practical applications in microelectronic and magnetic storage.

A theoretical study of the linear and non-linear local field inside multiple quantum wells (MQW) structure is undertaken. The electromagnetic response of a single quantum well of the structure is analyzed on the basis of the integral equation for the local-field inside the well. Both linear and non-linear optical response of MQW structure is described within the generalized transfer-matrix formalism. An example of matrix calculation for a well with a factorable conductivity tensor is considered.

The technique expanding the validity of single-beam Z-scan method for measurement of nonlinear-optical properties of various media based on paraxial approximation was developed. The comparison of various methods of nonlinear susceptibilities measurement interpretation was carried out. The agreement between values of nonlinear-optical parameters measured in extended and thin media was obtained.

The investigations of nonlinear-optical properties of crystals GaAs by a z-scan method are carried out. The concentration increase (> 10 times) of defects in a crystal GaAs due to picosecond pulse laser (τ = 35 ps, λ= 1.064μm ) irradiation at a number of laser shots >10⁴ near the optical breakdown threshold intensity was observed.

The behavior of the semiconductor dielectric susceptibility under the stationary action of a strong laser pulse in the range of M-band of luminescence and the test pulse in the exciton range of spectrum is investigated. The well pronounced Autler-Townes effect occurs at the exciton range. The position of the absorption peaks is determined by the amplitude and frequency of pump pulse.

Thermodynamic consideration of the photorefractive effect at the room temperature in the KDP group crystals is carried out in this work. As the result photorefractive coefficient is introduced. It's multicomponent character admits both the transverse and longitudinal components ofthe photorefractive effect, detected experimentally earlier.

The ionic probe-field spectrum is calculated including scattering in plasma. The peak of higher spatial harmonics is shown to broaden due to Coulomb dephasing. Account of the saturation and population effects provides an agreement with experiment.

We study the mechanisms of ultrafast free-electron generation in laser-irradiated dielectrics. The transient free-electron density in laser-irradiated dielectrics is calculated with a widely applicable new model, the multiple rate equation. The system of simple rate equations keeps track of the nonstationary electron energy distribution. We clarify the role of different ionization processes in dependence on laser pulse duration and intensity.

By all-optical poling of a medium the long-lived space-periodic electrostatic field arises inside the sample and, as a result of such induction, an isotropic medium gains the properties of an inhomogeneous optical single-axis crystal. The space distribution and the maximum value of the resulting induced electrostatic field in the present of the current mechanism of all-optical poling are substantially depending on the geometry of poling process in medium during the interaction of intersecting laser beams. All-optical poling process is theoretically studied at different conditions of two-beam interaction in an conductive isotropic media and the spatial distributions of the resulting induced electric fields are analyzed. The efficiencies and the features of the typical geometrical schemes of all-optical poling are discussed.

It is shown, that in case of proximity of group velocities of light and sound the nonlinear mode of the connected distribution acoustic and the optical waves is possible. It is described by nonlinear Shredinger equation. The estimation of critical capacity higher which comes the self-focusing of a beam is carried out.

Electromagnetically induced transparency in an optically opaque medium under the action of the radio-frequency field is experimentally demonstrated for exited atoms for the first time.

We show that in optically dense medium, consisting of three-level Λ-atoms, the effect of fractional stimulated Raman adiabatic passage leads to the maximum coherence on Raman transition to length of the medium considerably exceeding length of the linear resonant absorption. The general case of unequal forces of oscillators on the coupling transitions is analyzed. Results are of interest for a coherent anti-Stokes Raman spectroscopy with the delaying pulses.

The laser-induced processes in the fullerene-doped π-conjugated organic systems based on polyimide, 2-cyclooctylamino-5 nitropyridine, polyaniline, polymer-dispersed liquid crystals, etc. have been studied. The optical limiting experiments have been performed at wavelength of 532, 1047, 1080, 1315 and 2940 nm. The optical limiting threshold has been found. The reversible holographic recording experiments have been carried out at 532 and 1315 nm under the Raman-Nath diffraction conditions at spatial frequency of 100 mm^-1. The nonlinear refraction and third order susceptibility have been estimated from holographic recording data. The place of the systems studied among other materials used traditionally for nonlinear optics has been established.

The study of light scattering by the barium sodium niobate crystals has been performed in range of 20-800°C at the excitation of the crystal by argon (514,5 nm) and helium neon (λ=630.0nm) lasers. At heating from room temperature near 500°C the laser observed increasing far field spot dimension for λ=514.5 nm. It was observed also on heating, that the elastic light scattering intensity increases near the ferroelectric phase transition (T_c=550°C) for λ=632.8 nm in contrast with decrease for λ=514.5 nm. It have related our measurements to results of x-ray and electron microscope investigations by works.^3,4

A novel all-optical time domain regeneration technique using nonlinear pulse broadening and flattening in normal dispersion fiber and subsequent temporal slicing by an amplitude modulator (or a device performing a similar function) is proposed. Substantial suppression of the timing jitter of jitter-degraded optical signals is demonstrated using the proposed approach.

We study the importance of the linear optical properties of Langmuir-Blodgett films in their second-order nonlinear optical characterization. Second-harmonic generation with two noncollinear input beams is used to determine the susceptibility tensor of films of various thicknesses. In all cases, we find that the consistency of the results requires that the linear properties of the nonlinear layer be included in the model. While this is expected for the thickest films (~100 nm), our results show that the same holds also for a single Langmuir monolayer (~2,5 nm). Contrary to previous experiments on similar samples, we find that the linear response of a monolayer is well described by using the refractive index ofthick films of ~100 nm.

We present experimental studies and numerical simulations of pulse propagation in continuous and periodically-modulated nonlinear waveguides, in the anomalous dispersion regime. These reveal the complex dynamics ofthe beam trapping process in periodic structures.

The peculiarities of nonlinear transmission (reflection) of the supershort pulses of laser adiation by a thin semiconductor film due to the two-photon biexciton excitation from the ground state of the crystal. It is shown that the transmission is sufficiently determined by the amplitude, halfwidth and resonance detuning ofthe incident pulse and by the film thickness. The bifurcation region of the existence of the stable and unstable solutions is found.

Sensitive second-harmonic polarization measurements can yield important information about the symmetry properties of thin films. When the linewidth of the probe laser is relatively narrow, as in the case of a nanosecond pulse from a Nd:YAG laser, the polarization-sensitive optical components, waveplates in particular, behave according to specifications. However, the question arises, does this case also apply to a broadband source, such as a femtosecond laser pulse, where the linewidth is much greater than that of the waveplate? We show that the case does indeed hold by comparing measurements using both sources. However, special attention must be focused on the performance of the optics themselves, as manufacturer's specifications may not be accurate for each individual piece. The agreement of the measurements opens the door for determining the symmetry properties of completely new types of low-symmetry samples, such as gold nanoparticle arrays, which must be studied with a femtosecond source to avoid damaging the particles.

Shorter pulse duration and higher power of solid-state lasers have accelerated the development of frequency conversion technique using nonlinear optical crystals for laser precision microfabrications. Conventional theoretical-studies concerning frequency conversion supposed one pulse irradiation, accordingly the influence of temperature change of crystal induced by laser absorption is not considered, though practical frequency conversions are used with repetitive irradiation. Researches and developments of harmonic generation with repetitive irradiation have been approached experimentally or empirically. On the other hand it was reported in the previous studies that temperature gradient in the crystal is the cause of undesirable conversion in the harmonic generations such as either decline or fluctuation of the efficiency and distortion of beam profile. In this study, the second harmonic generation considering laser absorption was analyzed theoretically through a coupling model composed of truncated equations includes laser absorption and heat conduction equation. Influence of temperature rise of crystal induced by laser absorption with repetitive irradiation on conversion efficiency and output beam profile in SHG was investigated. It was shown that conversion efficiency decreases or fluctuates and beam profile of output second harmonic also changes complicatedly with repetitive irradiation, depending on the input condition. High temperature region moves from the side of output surface to the center of crystal during the continuing irradiation; the temperature difference in the crystal is not so large. Therefore, we concluded that temperature gradient naturally induced by laser absorption is not an essential reason of the undesirable frequency conversion.

New method to achieve high SHG efficiency under the conditions of phase mismatch and strong GVM with taking into account the self-action of femtosecond pulses is made. We show that the special low frequency modulation of the input pulse can be used to compensate negative influence of GVM. Formation of short pulse of basic wave and high intense pulse of second harmonic under strong GVM and phase mismatching are shown as well.

This work presents experimental studies into the energy efficiency of multiwave mixing in complex molecular media exhibiting higher order nonlinearities in two cases: volume holograms in the standard geometry of degenerate four-wave mixing and self-diffraction of the recording waves from thin dynamic gratings. The use of different combinations of mutually aligning polarizations for interacting waves enables one to determine the contribution into the interaction efficiency of various dynamic gratings and nonlinearity mechanisms. The role of polarization gratings resultant from spatial modulation of the light-field polarization state on orthogonal polarization of the hologram recording waves is established. Comparisons between the contributions of the polarization and "normal" gratings recorded by identically polarized light beams into the process of multiwave mixing demonstrate that the ratio of these contributions is dependent on the intensity of interacting waves. By variations in the propagation direction of a reading wave a change from four- to six-, eight- and ten-wave mixing may be realized.

Dynamics of self-pumping photorefractive loop mirrors will be considered. We will show that depending on experimental conditions as phase-conjugation with efficiency up to 70-80% as formation of unstable oscillating structures of soliton-like filaments can be realized.

In this work a theory of the four-wave mixing (FWM) is developed in a liquid suspension of transparent microspheres (heterogeneous medium), the nonlinearity of which is caused by the change in the microspheres concentration under the action of the gradient forces in the electromagnetic field of interacting waves. The effect of suppression of four-wave mixing because of the reduction of the resulting components of the gradient forces to zero for microspheres of certain sizes and certain angles of convergence of interacting waves have been predicted. A stationary regime of four wave mixing has been analyzed in the diffusion limit and the conditions of the appearance of parametric generation of a pair of mutually conjugate waves have been determined.

Peculiar light-matter interactions can break the rule that a single beam polarization can address only two states in a optical memory device. Multistate storage of a single beam polarization is achieved using self-induced surface diffraction gratings in a photo-active polymer material. The grating orientation follows the incident light beam polarization direction. The permanent self-induced surface relief grating can be readout in real time using the same laser beam.

The investigation of the transverse photorefractive effect by an interferometric method in KD*P crystal are carried out at its excitation perpendicularly of optical axis of the crystal on a wave length 1,08 microns. The results are compared with earlier obtained at excitation of the effect along an optical axis of the crystal.^1-3 It was found that the amplitude of the photorefractive field in longitudinal geometry of excitation is to adequate amplitude of a field in transverse geometry of excitation, truth at some magnification of the density of energy of stimulating radiation.

In the present work the results of the experimental investigations of the stimulated Rayleigh-wing scattering (SRWS) spectral, energetical and spatial properties are presented. SRWS was excited by single pulse of the Nd:YAG modelocked laser second harmonic. Scattering propagating in the direction opposite to the initial laser light was investigated. Acetone and water have been used as active materials. Experiments have been performed under different geometrical and energetical conditions of excitation. The transformation of SRWS spectrum in different excitation conditions has been studied. The existance of the two sharp lines in the SRWS spectrum has been found at some experimental conditions of excitation with frequency shift in the range of ~20 cm^-1. Transformation of this two-lines spectrum into one line spectrum was experimentally investigated as a function ofthe excitation geometry and initial laser pulse energy. Four-photon processes, leading to this effect, are considered. Spatial structure of SRWS at the same conditions of excitation has been studied. Possible applications of the SRWS for image processing according to the results on the SRWS spatial structure investigations are discussed.

Stimulated Brillouin scattering (SBS) of ultra-narrow frequency-stabilized 1.064 μm radiation in a fiber has been studied. Brillouin shift and gain coefficient have been obtained from the experimental data for conventional telecom (AllWave^TM) and phosphosilicate fiber. Output spectrum of one-stage phosphosilicate Raman laser generating at ~ 1.26μm with 1.08 μm YDFL pumping is shown to exhibit transition from one to several peak starting from threshold. It has been proved that these peaks are generated in SBS process.

Thermal velocity correlation function for a gas medium molecule is calculated. The velocity correlation time is found to be three times of the molecule mean free run time. The hydrogen molecule diameter is evaluated using data of the time-domain coherent anti-Stokes Raman spectroscopy.

The nonlinear dynamic phenomenon of the self-induced temporal instability of the light field, resonantly acting on the thin-film structure with nonlinear absorption, is described. Such effect has been observed in the case of excitation of a guided mode in multilayer structures by the prism-coupling technique with a low-power continuous-wave He-Ne laser radiation. This effect associated with the interface influence on the optical nonlinearity in thin-film structures.

The mechanisms of self-localization of electromagnetic radiation in a cold collisionless plasma of a spherical microcavity have been investigated. The possibility of soliton-like states realization of electromagnetic field and spherical plasmons self-localized in a finite volume ofmicrocavity has been shown.

We obtained the system of nonlinear differential equations for the areas of the envelopes the propagating supershort pulses in two guides of the coupler, which are the area theorems. We predicted the self-switching phenomenon for the energy transfer from one guide to the other. We investigated the phase portraits and predicted a number of new mechanisms of the pulse transmitting.

Solution, describing dynamics of few-cycle pulses under any angle to axis of the optical anisotropy of uniaxial crystal is received. In such media pulses are divided on ordinary and extraordinary components, interacting between itself in nonlinear mode. Ordinary wave include any number of light oscillations, and extraordinary wave is always video pulse. It is shown that spectrum ofordinary wave depends on sign of birefringence and angle of propagation.

The modes of nonlinear propagation of the two-component electromagnetic pulses through optically uniaxial media containing resonant particles are studied. The features of their manifestation in the "dense" media and in the media with expressed positive and negative birefringences are discussed. It is shown that exponentially and rationally decreasing solutions of the system of material and wave equations allow us also to describe the propagation of the pulses of the self-induced transparency in isotropic media in the case, when the direct electric dipole-dipole interaction between the resonant particles is taken into account.

The influence ofthe transversal perturbation on the self-similar monochromatic pulse, propagating in the inversed (gain) media is studied. It is found that two modes are possible: self-focusing and blowup defocusing with the forming the one-dimension pulse. The mode is determined by the value of the parameter μ, that defines the attitude of characteristic lengths ofdiffraction and dispersion.

The first observation is reported of the primary and stimulated femtosecond photon echoes at liquid nitrogen and room temperatures in a dye-doped polymer film at a wavelength of 780 nm. Echo signals were generated by pulses with the duration of 130 fs. The primary echo signal decay at a liquid nitrogen temperature can not be described by a simple exponential function. There is a fast decay region below 250-300 fs and a slow decay region at longer time intervals. The decay of primary echo signal at room temperature demonstrates complex behavior caused by the presence of the phonon-side band in the optical band of impurity centers. There were also detected signals of the self-diffraction of exciting pulses on a nonequilibrium population difference grating, induced in resonant medium by these pulses.

Enhancement of the refraction index accompanied by small absorption in a two-level atomic system imbedded in a photonic crystal for a resonant laser radiation under the action of the same radiation is shown.

The optical limiting action of C₆₀Ph₅Cl and C₆₀Cl₆ in solid host has been investigated at 532 nm with nanosecond pulses. The limiting thresholds for C₆₀Ph₅Cl and C₆₀Cl₆, were 8 J/cm² and 7 J/cm², and the linear transmittances were 22 % and 50 %, respectively. These results were compared with previous work, which was carried out on C₆₀Ph₅Cl and C₆₀Cl₆ molecules in toluene solutions. It was found a fair agreement between the two cases (solution and solid). This behavior can be understood on the basis of the reverse saturable absorption mechanism which determines the optical limiting properties of the C₆₀Ph₅Cl and C₆₀Cl₆ molecules. Such lower limiting thresholds make these compounds good candidates for optical limiting materials.

Disperse properties of biaxial mixed LiIn(Se_1-xS_x)₂, x= 0;0.5; 1, nonlinear crystals are investigated. Most useful Sellmeier equations for parent LiInS₂, LiInSe₂ and mixed LiIn(Se_0.5S_0.5)₂ crystals are identified from available and original results on disperse properties and experimental phase matiching angles for second harmonic generation. Modernized Sellmeier equations are proposed for parent crystals.