Formation of the limiting states of the laser pulses (both classical squeezing over time, i.e., compression, and quantum squeezing, i.e., suppression of fluctuations below the quantum limit) for a dynamic diffraction (scattering) in a spatially periodic medium are studied for the first time. The physics of the phenomena under consideration is determined by competition and energy exchange between interacting light beams and envelopes under the Bragg- resonance condition.

The results of theoretical and experimental investigations of thin nonlinear lenses excited by ultrashort laser pulses in various medium are presented. A theory of the optical systems containing thin nonlinear lenses in media with cubic and quadratic nonlinearities is developed. General properties of optical systems with thin nonlinear lenses and its applications to ultrashort pulses control are considered.

The results of experimental study and theoretical treatment of the evolution of the backscattered light pulse in statistically homogeneous disordered medium are presented. Scattering kinetics was measured for water solutions of the latex microparticles with time-correlated photon-counting setup and ML Ar -laser. It is shown that backscattered pulse arrived to photo detector with essential delay with respect to the pulse reflected from the surface of the scattering medium. This delay is due to angular anisotropy of the scattering. Backscattering of non-coherent diffuse component of radiation propagating in forward direction develops in inner layers of the medium and determines the value and concentration dependence of the backscattered pulse delay. 1.

The experimental studies on ultrafast relaxation processes in organic radicals are presented. Three mechanisms of ketyl radical formation are established and separated: direct transfer of a hydrogen atom as a whole; two-stage transfer of an electron and of a proton in an excited complex; and proton transfer at diffusion encounters of anion and cation radicals. The thiyl radicals formation at homolytical photodissociation of organic sulfides by picosecond laser pulses occurs at a rate constant k

New reversible bleaching polymethine dye 5105-U for spectral range of 1300 - 1750 nm is proposed and investigated. Its properties are compared with those of the 4919-U dye. It is shown that the new dye is promising for passive mode locking and Q-switching at wavelengths of 1300 - 1750 nm.

The picosecond pump-probe technique has been used to investigate the transient spectra and absorption kinetics of thermally evaporated VO-phthalocyanine film. The annihilation of excitations, heating of the film, and hypersonic strain wave generation were found to cause picosecond absorption changes after intense excitation. Hypersonic strain waves were determined to manifest most significantly in the region of a charge transfer absorption band. This fact is explained by the sensitivity of the transitions with intermolecular charge transfer to the distance between interacting molecules.

By picosecond spectrometer with two tunable dye lasers, high temperature superconducting (HTSC) (monocrystal Y-Ba-Cu-O with critical temperature Tc equals 87 K) and metal (Ni) thin films have been investigated. A self-diffraction process efficiency (eta) versus biharmonic pumping component detuning (Omega) has been measured at the temperature (Theta) equals 300 and 80 K. It is found that there is a well-defined dip on the dispersion curve (eta) ((Omega) ) for the HTSC films at (Theta) equals 80 K and -10 cm-1 (Omega) -50 cm-1. This region upper limit corresponds to a superconducting energy gap value 2(Delta) . At 10 cm-1 -1, any distinction of the same type is absent. In other respects all obtained dispersion curves are similar. They consist of the central peak ((eta) approximately equals 10-7, (Omega) -1) and wide wings ((eta) approximately equals 10-9, (Omega) 10 cm-1) with the interference structure. Y-Ba-Cu-O film resonances are coincided with the phonon mode frequencies (120, 335, and 580 cm equals -1). It is shown that photoexcitation kinetics (the sample ''darkening'') must consist of some components. A characteristic time of the most ''ultrafast'' component below 5 fs has been estimated and a complex subpicosecond quantum beats presence has been predicted.

Interband absorption of a short pulse of light leads to the reversible bleaching of a sample within picosecond time range. After the pulse at times less than that of spontaneous recombination, a plasma state depends neither on the pulse energy nor on the energy of exciting photons. Radiation has been observed that correlates with excitation at picosecond times. Mechanisms of the phenomena have been studied. The paper describes an investigation of alterations in optical transparency of thin epitaxial layers of GaAs due to irradiation by a powerful pulse of light having a picosecond duration and the photon energy $HBAR(omega) ex close to the band gap Eg. The paper deals with those experiments as well as a set of experiments intended for clarifying the nature of the observed phenomena.

Methods for the nonlinear refractive index measuring in a dissipative medium are elaborated. The fast nonlinearity dispersion is measured in (alpha) -SiC(6H) crystals in the intersubband absorption range (hw approximately 2 eV). The conclusion is made regarding silicon carbide nonlinearity mechanism.

The results of experimental investigation of cubic nonlinearity and Raman conversion efficiency dependencies on Nd-concentration in potassium gadolinium tungstate:Nd crystals are presented. These results are explained based on two-photon resonance and parametric processes theory.

Formation of coherent Stokes components from spatial-temporal spontaneous noise during stimulated Raman scattering (SRS) is investigated theoretically and experimentally. The formation conditions of coherent Stokes radiation with parameters independent of initial noise distribution are found in the case of forward Raman scattering of coherent laser ultrashort pulse. The dependence is examined of coherent Stokes radiation parameters on characteristics of Raman-active medium and parameters of pumping pulse with Gaussian spatial and temporal profiles.

Stimulated Raman scattering (SRS) of ultrashort pulses at saturation stage is investigated both theoretically and experimentally. A theory of light intensity self-limiting in Raman media concerning the peculiarities of Stokes wave amplitude-phase spatial transverse distribution is developed. Conversion modes classification based on nonstationary SRS theory, taking into account the parameters of coherent Stokes pulses formed from noise distribution at initial stage of SRS process, is represented. Stable polychromatic 10 ps pulses have been obtained in YAG:Nd³⁺ laser with intracavity Raman conversion in potassium gadolinium tungstate (PGT) crystal.

The possibility of increasing the light transformation efficiency into SHF range by means of nonlinear crystal partially filling cross-section of the waveguide is suggested, theoretically grounded, and experimentally realized. The phase matching condition is provided by the degree of partial filling. Difference frequency radiation slowing factors and optimal thickness of LiNbO₃ crystal are calculated for USP generation within the range of 2 - 46 mm. USP SHF train with a frequency repetition of approximately 10⁸ Hz and transformation efficiency in energy pumping up to 28% of maximum value is obtained.

Cross-correlation method of measuring the optical and electrical waveforms with picosecond time resolution is reported. Sampling pulses (duration 5 - 15 ps) were generated by injection AlGaAs laser. Electro-optical Pockels effect was used for electrical measurements, and sum- frequency generation was used for optical measurements.

A passive feedback control in an actively mode-locked pulsed Nd:YAG laser was used to shorten the pulse duration or obtain millisecond trains of ultra-short light pulses. The intracavity second harmonic generation in a crystal situated at proper distance from the output mirror served as a positive or negative feedback. When negative feedback was used, the length of the train was limited by the length of the flash lamp pumping pulse.

A powerful new technique for the generation of stable ultra-short laser pulses is reported. The basic idea of the method is to couple back a tiny fraction of the laser output into the main laser cavity. This coherent seeding signal suppresses the deleterious influence of the spontaneous emission on the pulse formation to a large extent that results in a considerable improvement of the laser output stability. Experimental results for two different laser systems are presented together with numerical simulations that serve to illustrate the principle of the technique.

Numerical simulation of self-modelocking of cw solid-state lasers with Kerr polarization modulator is developed. The limited ranges of laser and modulator parameters within which the laser generates stable train of ultra-short pulses are given.

Small duration of a metal vapors laser oscillation pulses can be obtained using the mode- locking phenomena. To obtain an effective mode-locking, a laser with an active medium of small length, a short cavity, and a big modulation depth index should be used. For calculation of a mode-locking phenomena, the density matrix equations are used in the semiclassical approximation.

A terawatt-class laser system based on the amplification of tunable femtosecond pulses in an electron beam pumped XeF(C-A) excimer amplifier is reported. For this system the characteristics of gain, saturation, energy, and pulse shape is described theoretically and experimentally, particularly their dependence on input pulse duration, gain length product, and nonsaturable absorption. Using an optimized unstable resonator, this XeF(C-A) laser system generates 275 mJ, 250 fs pulses at 490.5 nm.

The development of a Ti:sapphire-based femtosecond system capable of producing high repetition rate and high power output that is tunable from the near-ultraviolet to the mid- infrared is reported. This is achieved using the nonlinear optical processes of optical parametric oscillation and second-harmonic generation that results in sub-100 fs pulses and hundreds of mW of power across the full tuning range.

A survey is given on recent developments in ultrashort-pulse 10 micrometers OFID CO₂ and far-infrared gas lasers as well as on the new distributed- and helical-feedback gas lasers.