We present the results on stimulated Raman scattering in hydrogen excited by 200 fs-duration 1 kHz repetition rate and 0.6 mW average power Ti:sapphire laser (780 nm) and 0.2 W average power second harmonic (390 nm) pulses with linear and circuit polarization. We report on the spectral and temporal measurements of the various generated vibrational and rotational components at Stokes- and anti-Stokes frequencies in the wavelength range 289 - 1154 nm. At optimal conditions at 390 nm pump wavelength the SRS signal of 30 mW average power was obtained at the first (465 nm) and the second (577 nm) vibrational Stokes. The shortest measured duration of the vibrational Stokes components was by 3 times less than the duration of the pump pulses.

In LilO₃ and BBO crystals noncollinear parametric generation with tuning range 0.45 - 2.9 micrometers is investigated by pumping with the second harmonic of 150 fs Ti:sapphire laser pulses. In LilO₃ propagation angles simultaneous phase- and group-velocity-matching are determined. Noncollinear parametric amplification with the wavelength tunability from 0.6 to 1.2 micrometers is demonstrated.

Laser pulses with duration of approximately one optical period have become the subject of theoretical and experimental research in recent years. The application of the traditional method of slowly varying amplitudes , which has been used for picosecond pulses, becomes impossible in this case, when the pulse duration is several times greater than the period of the carrier wave. In the case of limited short pulses, the concept of the carrier frequency loses meaning. The other approach is called FD-TD (finite difference time-domain) 2-4 , as far as the reduction of the duration of the femtosecond pulses demands a reduction of two-dimensional grid by one step on t and z, that leads to lowering of this method's effectiveness. In the present work is used the method connected with Fourier Transform of field values which allows us to introduce the electric inductivity. Although this method is connected with the introduction of two extra operations (direct and reverse Fourier Transform) for limited short pulses, it might be more efficient in comparison with the FD-TD method, since for homogeneous media it leads to simple equations for Fourier amplitudes. In addition, the application of the method based on Fourier Transform allows one to analyse the processes associated with pulse propagation, both in time and in spectral presentation.

The results of analytical and numerical investigation of the propagation of space-limited ultrashort (pulse duration is shorter than all the relaxation times and the time scale of the medium response) light pulse in Raman-active media are represented. This process shown reveals a number of novel specific features. It is found that at definite pulse energy the self- induced focusing is replaced by the self-induced defocusing which is again followed by the selffocusing. As a result a light channel which consists of a train of moving focuses occurs on the light beam axis. The rate of self-induced focusing and defocusing processes for this propagation regime is inversely proportional to the pulse field intensity, which is contrary to the conventional selffocusing theory.

The propagation of an intense femtosecond pulse in a Raman-active medium is analyzed. An analytic solution which describes in explicit form the evolution of the light pulse is derived. The field of an intense light wave undergoes a substantial transformation as the wave propagates through the medium. The nature of this transformation can change over time scales comparable to the period of the optical oscillations. As a result, the pulse of sufficiently high energy divides into stretched and compressed domains where the field decreases and increases respectively.

Spatial intensity modulation of luminescence in crystals excited by ultrashort pulses decays with respect to distance due to outrunning of the wave packets corresponding to the ordinary and extraordinary waves. The dispersion spreading of the packets introduces distortions into this picture. It is shown that these distortions become significant at pulse duration less than 0.1 ps.

The physical principles of a streak camera capable of sub-femtosecond time resolution are discussed. In place of the traditional photocathode, a distributed medium is used. In place of rapidly changing voltage applied to the deflection plates, we use an electromagnetic field propagating in free space. The basic technology for the sub-femtosecond streak camera is the same as that of above-threshold ionization experiments that have become very common in studies of strong laser field interactions with atoms.

We report a new principle for temporal measurements of pico-femtosecond scale using fiber- optic compression technique. Registration of both laser and non-laser pulses are analyzed on the basis of analytical and numerical studies.

A new method for USP laser intensity autocorrelation function measurement on the basis of its recording in microwave band is suggested and realized. The application of microwave radiation expands the spectrum boundaries of the correlation method both in VUV and in IR regions of spectrum. This method may be used in those cases where the SHG is inapplicable or low efficient.

The static triplet-triplet annihilation reaction kinetics in polymers by means holographic technique is investigated. The annihilation stage of the reaction T + T yields 0 is visualized by measurements of the diffraction picture dynamics. A theoretical model for the static annihilation kinetics is studied. The analytical expressions for the first and second diffraction maximum intensity are obtained.

The results of inverse problem solution for photothermal diagnostics of inhomogeneous medium are presented. Fast, effective algorithm for layered medium is considered. The method is valid for relatively wide range of differential equations and gives fast reconstruction of 1D thermal parameter profiles for the case of smooth inhomogeneities of arbitrary value. The numerical simulation results are also given. The represented stochastic approach is valid for thermal parameter fluctuations of arbitrary depth.

Threshold and polarization characteristics as well as temperature dependence of a two-band generation of laser with distributed feedback based on induced cholesterical liquid crystals (CLC) were studied. Difference between threshold excitation intensities of these bands of generation points at the existence of two phase gratings in the helical structure of CLC. It is verified by the difference in the temperature behavior of the wavelengths of the central lines of the bands.

The spectrometer is described designed for studies of the small deviations in inhomogeneously broadened systems under selective laser excitation as well as for time-resolved analysis of irreversible photochemical processes after single-shot excitation. The set-up includes tunable pulse laser and registration system based on CCD-array. Computer control and built-in memory for 256 frames provide sensitivity of about 0.002 optical density units when studying differential absorption spectra and time-resolved single shot spectral measurements in the millisecond range.

The automated IR-spectrometer based on the pulsed tunable (1.5 divided by 3.7 micrometers ) optical parametrical oscillator with a spectral resolution of 3 cm^-1 and the optothermal phase-contrast detection system is created. A minimal detectable absorption level is as small as (alpha) equals 10^-6 cm^-1 at the heating energy of 10 mJ.

The spectral dependence of ultrafast relaxation of excitations in a C₆₀ thin film was discovered with the help of femtosecond laser spectroscopy. The dependence can be explained by the relaxation of excitations in different energy bands. The temporal dependence of photoinduced darkening is characterized by peak at delays of the order of pulse duration (approximately 50 fs). The peak is replaced at greater delays by a decrease with characteristic times (tau) ₁ equals 0.4 ps and (tau) ₂ equals 30 ps, determined by the relaxation of electrons on intramolecular and intermolecular oscillations. The spectral dependence of two- photon absorption is investigated.

By studying the temporal behavior of the optical density of C₆₀ thin film with the help of femtosecond laser spectroscopy the coherent phonon oscillations in the frequency region 10 - 400 cm^-1 (including with odd symmetry) in the wide spectral region of probing h(omega) _pr equals 1.78 divided by 2.34 eV was detected. Spectral dependence of photoinduced response permits to observe selectively the relaxation of electrons in different bands. The possibility of reversible polymerization in excited state is discussed.

Dispersion of low frequency polaritons have been studied in PbTiO₃ crystal in the 200 - 3000 cm^-1 wave vector range. Their behavior allows a new insight into the description of the internal processes involved: A₁-symmetry pure damped oscillatory response and E-symmetry more complicated mechanism.

Time-resolved resonant nonlinear optical response of C₆₀ in a chlorobenzene solution was measured for 528 nm excitation and 1055, 528, and 351 nm probing for zzzz and zzyy configurations. The slow part of the signal (8 +/- 2 ps) was attributed to the orientational motion of C₆₀ excited molecules.

A three-color, three-step, three-photon ionization scheme is chosen to examine the population dynamics and photoionization of isotopes in Yb media in the framework of the Maxwell-Bloch equation for the case where the laser frequencies are resonant on the transition lines of ¹⁶⁸Yb. It is revealed that the scheme can be used for the effective photoionization of ¹⁶⁸Yb, resulting in a selectivity of about 100%.

Transient hole-burning and free induction decay (FID) in low-temperature ion-doped crystals are studied consistently using the model of two jump processes U^t equals U^t₁ + U^t₂ characterized by essentially different jump rates v₁ >> v₂ and distribution widths (sigma) ₁ << (sigma) ₂ for the impurity ion optical transition frequency fluctuations U^t due to the bulk and the frozen core spin flipping. At short pump/probe pulsewidth T and short delay time (tau) _d ((tau) _d, T << v₂^-1) the calculated hole shape is narrow with the hole width determined by U^t₁ process characteristics only. The hole width in this case coincides with the calculated FID rate. At long delay (tau) _d >= v₂^-1 the hole becomes a wide lorentzian with the halfwidth 2(sigma) ₂. The theory fits well the experimental data by A. Szabo et. al. on narrow hole burning and FID in ruby under low and high magnetic fields supposing the fluctuations U^t₁ to be rather slow ((sigma) ²₁/v²₁ equals 0.5).

Bleaching and darkening occurring in thin-film matrices with high concentrations of doped microcrystallites were explained in terms of the filling of quantum-well and surface energy levels with carriers excited by the picosecond laser pulses. The possibility of creating of the picosecond optically controlled interference and cavityless switches is discussed.

In this work we present the results of two-wavelength rotational CARS thermometry (2(lambda) -CARS thermometry) of hydrogen at temperatures from 300 K to 1100 K. Experimentally, temperature was measured in a heated cell using single-shot and averaged CARS intensities in the rotational S-branch. Relative standard deviation for single-shot temperature values was approximately 1.5% at 296 K and approximately 8% at 1000 K. The accuracy achieved, its dependence on measured temperature, and possibility of their improvement were analyzed.

Starting from the infinite-order sudden approximation, the tetradic collisional relaxation cross- sections may be expressed in terms of dyadic cross-sections. It is shown that the energy corrected sudden approach leads to a correct prediction of the spectral profile unless the characteristic macroscopic relaxation times are introduced in the model. Consequently, a few number of fitting parameters allows us to predict infrared, stimulated Raman or Coherent Antistokes Raman profiles within the experimental accuracy. The generalization to any excited vibrational mode is straightforward.

The vibrational kinetics of nitrogen in a shock wave was studied with use of broadband CARS. We compared the results of our own calibration tests of time relaxation of pure nitrogen with those obtained by other authors. The conclusion was made that this method (CARS) is adequate in studying of relaxation phenomena of the molecules in shock waves. The rates of a VV' exchange in mixtures N₂-O₂ was measured. We estimate the lower bound for the time of de-excitation of energy exchange between molecules and atoms of nitrogen.

We propose new and promising procedure for nonlinear spectroscopy of high-T_c superconductive thin films. It enables us to determine the phase transition temperature, superconducting energy gap width, interaction constants, etc. For Y-Ba-Cu-O thin films, we present our results in testing of this procedure including investigation of relaxation kinetics after picosecond optical excitation of the film.

The combined effect of electrostriction and radiative absorption in the formation of laser induced gratings in fluids is calculated. For pure electrostrictive gratings, the reflectivity is a damped oscillation with alternately higher and lower maxima. The damping is determined by viscosity and heat transfer. The normalized difference in height is determined by the thermal conductivity of the medium. Therefore, in principle, a separate determination of viscosity and thermal conductivity is possible. Measurements have been performed in the nonresonant or pure electrostrictive domain for argon and nitrogen.

The nonresonant laser induced non-linear optical activity in a solution of L-amino acids has been investigated for the first time. The experimental data on optical polarization rotation of a laser beam are presented and have been used to determine of the third-order molecular susceptibility for the process of interest.

Coherent four-photon scattering of light due to excited and autoionizing states of atomic systems is considered. We analyze the influence of one-photon resonances at the frequency of the anti-Stokes signal and at the frequency of the pump wave on the shape of the spectrum of four-photon scattering. We derive analytical expressions for the line shapes of four-photon scattering involving one-photon resonances with allowance for phase-matching conditions and variation in the populations of excited states for limiting regimes of tight focusing and strong absorption in a medium with a cubic nonlinearity. The calculated spectra of four-photon scattering include the interference of resonant and nonresonant components of the third-order nonlinear susceptibility with allowance for one-photon saturation. We develop a method for normalizing experimental spectra of four-photon scattering with one-photon resonances that takes into account distortion of spectral lines due to the influence of phase mismatch and one- photon absorption.

Self-diffraction of light waves in `dye + polymeric matrix' medium is analyzed by means of simulation methods. For the mechanism of resonance nonlinearity the diffraction efficiency is optimized and dispersion characteristics of the first maximum are obtained. The contributions of different mechanisms of grating recording are evaluated for the experimental results.

Using carbon dioxide lasers it is possible routinely to obtain saturation spectra in the 10 micrometers region at linewidths below 20 kHz. A complementary double resonance technique uses a carbon dioxide laser to saturate a vibration-rotation transition while probing the molecule with a radio frequency. These two techniques are combined to obtain data on nuclear hyperfine structures in molecular spectra, which in turn are used to test and extend current theoretical models.

The profile of nonlinear resonance in the probe-field ionic spectrum is shown to narrow down with the saturating field detuning. Physical cause of the effect is the falling velocity dependence of Coulomb collision frequency.

The action of pulsed CO₂ laser (power density of 10⁷ W/cm², length of pulse 200 nsec) on the surface of the synthetic single crystal quartz has been investigated. The experiments have shown that the stable hole burning in infrared reflection spectra just at the frequency of laser action was appeared. The hole with a half width of 4 cm^-1 was burned in the reflection spectra of irradiated samples. The photoluminescence and electron spin resonance investigations have shown, that this hole burning is connected with destruction of Si-O bonds and with appearance of a several different defects centers.

High resolution intracavity laser spectrometers were developed in 8000 - 11000 cm^-1 spectral region. Threshold sensitivity of the spectrometers (10^-7 - 10^-8 cm^-1) allows one to carry out effective investigation of high vibrational-rotational water vapor states at low and high temperatures. Vibrational states of H₂¹⁶O, H₂¹⁸O, D₂O and HDO were investigated in a spectral region up to 11000 cm^-1. Spectroscopic parameters were determined and vibrational parameters were used for calculation of the vibrational energy levels up to 16000 cm^-1. New types of resonances between states of different polyads have been found.

The fine structure of highly excited atomic and molecular states has been investigated suing high sensitive intracavity laser spectrometers with spectral resolution within the interval from 0.018 to 0.05 cm^-1 and at minimum detectable absorption coefficients in the 10^-7 - 10^-8 cm^-1 range in the visible and photographic infrared regions.

The methane absorption spectra were obtained behind a shock wave (temperature 1370 K), at 293 K by devised nonlinear IR spectrograph. The spectra calculated on the basis of HITRAN92 data accord with experimental ones. The possibility of temperature determination of methane containing mixture on absorption spectra shape is discussed.

The dependencies of two-photon excited luminescence intensity on the exciting laser radiation energy have been studied. As a source of pumping light we have used Q-switched ruby laser, and luminescence has been recorded in the blue and near ultraviolet region. The experimental results have been obtained for some aromatic solid state compounds as anthracene, stilbene, POPOP and 3,4,5 trimethoxy benzoic acid. We have established essentially nonlinear behavior of investigated dependencies with saturation at the large pumping energy: 0.2 - 0.8 J. The opportunity of superfluorescence, appearing under two-photon pumping of aromatic solids, was analyzed.

The photophysics processes in model biological systems types micelles-polymer structures was investigated by laser fluorescence spectroscopy. The fluorescence probe applied to study complex formation and determination of the local dynamic of this system. The energy transfer in donor-acceptor pairs are studied spectroscopically.

The multiply scattered light intensity was measured when a narrow laser beam illuminated a turbid medium. The position of the pointlike effective diffusive source appeared to be unexpectedly deep. It is important in diffusing-wave spectroscopy.

Slow particles effect is detected for the first time in kinetics of molecular gas coherent response in transit time conditions. Coherent responses decay rate reduction at elevated time delays demonstrates ability of slow particles employment for high resolution coherent spectroscopy.

The facilities of the coherent laser pulse spectroscopy of the pHe⁺ transitions are considered taking the magnetic structure of the energy levels into account. The possibility of observation of the dynamics of `intramolecular' motions is also analyzed.

A Doppler-broadened 3-level atomic Yb medium is chosen for the study of efficient selective excitation in the framework of the Maxwell-Bloch equation. It is examined if laser pulse propagations can excited most ¹⁶⁸Yb atoms to the third levels without significantly influencing other isotopes in the ground states.

The possibility of using OPO and two-cascade OPO-SRS converters is considered both for the generation of probing pulses and for the amplification of radiation scattered in the atmosphere. The lidars based on such combined use of OPO and OPO-SRS converters are protected against the background radiation and ensure the probing distance in the IR a few times greater than when the conventional lidars are employed. It is shown that the use of two-cascade parametric and multicascade SRS image amplifiers will make it possible to record the spatial distribution of ultrashort radiation attenuated by a factor of 10¹³ divided by 10¹⁴, having an energy of order 1 mJ, for about 10² image cells.

Using the ultrashort IAG-Nd laser pulses as the IR pump ones the effective cascade stimulated Raman scattering (SRS) in hollow-core optical fiber, filled by liquid bromine was investigated with picosecond time resolution. On the basis of transient SRS theory the nonlinear response of liquid bromine was discussed and the vibrational dephasing constant T₂ was determined for the first time.