The operations at VNIIEF large-sized laser facilities and the VNIIEF advanced projects of laser facilities for ICF and fundamental physics investigations are discussed. Iodine laser and phase conjugation physics are treated. The possibility of the monopulse laser channel development is shown with energy up to 70 kJ in the single beam. The paper presents the brief review of the 10 MJ laser project and the high explosive photodissociated iodine laser (HE- laser) with phase conjugation is considered as the possible way of solving the ICF problem in the fast ignition concept. We suggest the way of the quasi stationary superhigh light field production by the focusing of power laser beams into supersmall volume (wavelength order size).

Solution of the problem of creating efficient phase conjugate mirrors (PCM) for radiation of cw chemical lasers (CWCL) will make it possible to extend the scope for applications of high- power low-divergence radiation in the 2 - 3 micrometer spectral region which currently draws active interest. Both four-wave mixing (FWM) and stimulated Brillouin scattering using some threshold decreasing schemes can be employed as a technique for implementation of an efficient PCM for the lasers of this type. In this paper, we present the results of the phase conjugation implemented for the CWCL radiation using the FWM in a liquid with thermal nonlinearity. This mechanism has been studied in detail as applied to the cw carbon-dioxide lasers, for which it so far remains to be the only technique for creating efficient PCMs. Threshold-free PCMs based on the FWM process in absorbing liquids are capable of providing nearly 100% reflectivities and may find application for dynamic aberration correction in the optical paths, coherent addition of laser radiation channels, and for laser beam direction control.

Phase conjugation by SBS (stimulated Brillouin scattering) is a powerful and simple tool to increase the beam quality of high power lasers up to the diffraction limit. Master oscillator and power amplifier systems with Nd:YAlO as active medium were realized with an average output power up to 210 watts at 1.08 micrometer in a near diffraction limited beam. Also Nd:YAG-oscillators with phase conjugating mirrors were realized with an average output power up to 17 watt and high beam quality. In the UV range, excimer oscillators with SBS mirrors deliver the same or better beam quality than conventional plane-plane resonators in 3 times shorter pulses. Excimer oscillator-amplifier arrangements have been realized with SBS mirrors. SBS mirrors for the visible and ultraviolet spectral range are well characterized. First experiments for an ordered passive fiber bundle with an SBS mirror show the possibilities and limitations to improve the beam quality of fiber bundle amplifies or even oscillators.

The influence of the lens focal distance, the spectrum width and power of exciting radiation on the efficiency of phase conjugation is studied. The maximum coefficient of reflection 70% is obtained. The laser system is created which comprises the master generator, the quantum amplifier, the phase-conjugating mirror with the diffraction quality of the output radiation.

We report Q-switching of a Nd:YAG laser with a phase-conjugation mirror based on external external stimulated Brillouin scattering in CS₂, using a ring resonator. Pulses with 5 mJ minimum energy and duration of 15 ns, at 2 Hz repetition rate, in the TEM₀₀ mode were generated. A numerical simulation of the Q-switching regime has been made and good agreement between theoretical and experimental data has been obtained.

The theoretical and experimental investigation results for the regenerative regime of the 4- passes YAG:Nd laser amplifier with phase conjugation SBS mirror are presented. The role of the abnormal dispersion and Kerr nonlinearity of the active element on the forming of the output radiation parameters are shown. The gain of the amplifier 2.5 multiplied by 10⁴ was obtained experimentally.

Transverse stimulated Brillouin scattering (TSBS) in anisotropic crystals is investigated experimentally and theoretically. A computer model of TSBS in anisotropic media was developed and calculations were conducted of TSBS characteristics anisotropy and parasitic Stokes radiation growth. Experimentally characteristics of TSBS were defined by the method of SBS excitation in the transverse resonator. As a test medium fused silica was used. Medium characteristics were deduced from comparison of experimental oscillograms and analytical solution of SBS generation equations averaged over the resonator length.

Self-pumped phase conjugation of the light beam in an inverted Nd:YAG-crystal with the different schemes of the feedback loop has been studied experimentally and theoretically. The quality of the phase conjugation of space heterogeneous beam, and the vibrational resistance for different polarizations of the input beam were investigated. The thresholds of parametric generation of the phase conjugated beam in the inverted media with real and imaginary parts of the nonlinear susceptibility are discussed.

Investigations of self-pumped phase conjugation (SPPC) of a low power cw-Ar-laser by using a dye-doped nematic liquid crystal are reported. The phase conjugated signal was generated by stimulated thermal scattering. The threshold power at a wavelength of 514.5 nm was about 30 mW and the maximum power-reflectivity was up to 1%. The ability to compensate phase aberrations has been demonstrated.

We present a method to achieve phase conjugation based on saturable-gain degenerate four- wave mixing in the laser medium itself. Experimental and theoretical investigations show that phase conjugate reflectivities and efficiencies higher than 100% can be achieved with such an interaction. High conjugate-reflectivity at (lambda) equals 1.06 micrometers is demonstrated in conventional flash-pumped Nd:YAG amplifiers and in compact diode-pumped Nd:YVO₄ amplifiers.

Experimental and theoretical optimization of FWMF scheme parameters with hologram recording by thermal nonlinearity for YAG:Nd from the viewpoint of its energetic efficiency has been carried out. The optical efficiency has achieved 60% at the generation pulse energy of 200 mJ for a 2-mm input beam with the energy of 50 mJ. Normal operation of the scheme in the repetitive-pulse regime (up to 25 Hz) has been demonstrated.

Laser which contains additional self-conjugated loop resonator is investigated. Under certain conditions the improvement of laser efficiency is observed. Output laser emission possess TEM₀₀ divergence with good filling of intracavity aperture. The present paper is devoted to investigation of the energetic and spatial characteristics of the multi-mode aperture laser with ALR. A comparison of the laser parameters with that of the laser with a usual resonator is carried out.

Four-wave phase conjugation of YAG:Nd laser radiation in LiF:F₂^- crystals is demonstrated theoretically and experimentally. The generation regimes and technological possibilities of YAG:Nd laser system with parallel connection of active elements was investigated in passive Q-switching and phase conjugating by LiF:F₂^- crystal.

The decay time dependence and frequency dispersion of third-order nonlinear optical response in substance are analyzed in connection with a goal to realize efficient and fast PC mirror for middle infrared laser radiation. Some peculiarities in realization of PC mirrors at different wavelengths are discussed.

It's shown that the effect of two-photon free carrier generation (TFCG) in semiconductors is the most promising for achieving high DFWM reflectivities R with short enough decay time tau in wavelength range from 1.5 to greater than 9.5 micrometers. The materials which allow us to achieve R up to 100% with tau of order of nanoseconds for the range of interest are presented. Some specific features of DFWM via TFCG were studied experimentally in InSb at lambda equals 10.6 micrometers and in Ge at lambda equals 2.94 micrometers.

Pulsed energy deposition into a high power carbon-dioxide gas discharge as well as high pump energy deposition into a solid-state laser material results in a distortion of the transverse mode profile of the laser beam. In the first case the transverse field distribution is influenced by the laser induced medium perturbation and shock waves due to the inhomogeneous energy deposition into the amplifying medium. For the second case the known thermal lensing problems occur in optically pumped systems, flashlamp- and diode-pumped, respectively, under various pump power levels. The technique successfully applied in both cases for correcting the distorted phases is by means of phase conjugation. Through numerical simulations using the Fresnel-Kirchhoff diffraction theory by including the relevant beam distorting effects for the individual laser a restoration of the beam quality was found when a phase conjugate mirror (PM) was installed. These findings agree well with experimental results.

The ring cavity oscillation at the four-wave mixing in the carbon-dioxide-laser medium with feedback loop was studied. The cavity output energy about 5 J at the master oscillator energy of 0.5 J was observed, the phase conjugation fidelity ranged from 0.3 to 0.8.

The spectra of reflectivity and transmissivity of gain gratings induced by cw CO laser radiation in a flow active medium were calculated. Strong variations in the reflectivity spectrum for the different sets of relative phases of the interference fields were disclosed.

Laser induced medium perturbation (LIMP) influence on injected laser beam profile recovery was studied with the help of numerical simulation of pulsed double-passed carbon-dioxide- amplifier with the OPC-mirror. It was determined that gain fluctuations due to LIMP limit the recovery quality.

The paper presents experimental results on large scale carbon-dioxide-laser beam direction, using the telescope with nonlinear-optical dynamic compensation for distortions. Variants, using phase conjugation mirrors on base of SF₆-cell and of intracavity four-wave mixing, are discussed and compared.

The characteristic features of the conjugate wave's formation under transient four-wave mixing in a two-level medium are investigated. The phase modulations of the signal and conjugate waves induced in the four-wave mixing are not mutually conjugate and have the same sign. The fulfillment of the phase-conjugation for the phase modulated signal has been shown in particular to be connected with the envelope's deformation and the spectrum's change of signal pulses. The transient optical bistability connected with the nonlinear absorption's saturation in the quasi-cw four-wave mixing and with the inertia in the short pulse's regime is observed.

The possibility of phase conjugation with simultaneous doubling of the light-wave phase and frequency upon nondegenerate four-wave mixing has been suggested and substantiated theoretically. The dependence of the energy efficiency of double-phase conjugation on the spectroscopic characteristics of the multilevel resonant media has been analyzed.

Imaging of remote objects from space with the use of high-spatial resolution telescopes is a vital problem for a number of applications. Enlarging the primary mirror diameter aimed at increasing the telescope resolution is limited, on the one hand, by a dramatic growth of its cost with diameter, and on the other by the complexity and cost of a system that is necessaiy to maintain the mirror shape with high accuracy in realistic conditions of thermal and gravitational loads. Recently various adaptive techniques for correction of static and dynamic aberrations in telescopes have been developed. They allow in principle to enlarge the primary mirror due to the use of multisegment constructions when separate segments are phased to achieve the ultimate system resolution determined by the priinaiy mirror diameter. However, all these techniques, based on the use of beam wavefront analyzers, active minors with a lot of actuators and control electronics, are rather sophisticated and limited in response time, the number of actuators and of segments to be phased. For this reason, in parallel with traditional adaptive optic techniques some other approaches to the problem, based on the use of nonlinear optics techniques, have been progressing last years. One of the promising solutions for high-resolution imaging with the use of poor - quality optics is based on illumination of remote objects by laser radiation and their observation in reflected coherent light 2, It gives the opportunity to apply phase conjugation (PC) techniques, developed for coherent laser radiation, for correction of aberrations of the segmented mirror. The correction concept uses such a design that the reflected from the object laser beam coming to a certain point of the primary passes through this point twice, first propagating from the object and second after phase conjugation, when it goes in backward direction. As a result the distortions introduced by the primal)' mirror are canceled. To create the image of the object not at the object itself, as it should be due to phase conjugation, but at some plane located within the telescope, the additional quadratic phase correction can be introduced into the beam with the use of polarization technique when it goes back from the phase conjugate mirror (so called "by - pass concept") 2 The difference in angles of incidence of the beams at the direct and backward passes is one of the most important factors limiting a degree of phase -conjugation correction of aberrations; especially at large f - numbers. However, the degree of primary aberrations reduction due to phase conjugation can be very high in such systems and amounts to tens or hundreds.

The reflectivity of UV-laser beams under degenerate four-wave mixing in solid-state and liquid media is calculated in the case of electrostriction nonlinearity. It is shown that the response time of DFWM is quite short and its efficiency is high in comparison with SBS. We believe that such DFWM-mirrors can be efficiently used as PC-mirrors in UV. In theory the possibilities of a nonlinearity electrostriction mechanism for degenerate four-wave mixing (DFWM) of excimer lasers radiation have been analyzed. It should be noted that these lasers require a high speed response of a nonlinear medium. The dynamic fine (small) scale grating providing phase conjugation (PC) of pulse excimer lasers with a reflection coefficient by several tens of percentage has been demonstrated to have little response time (less than 10^-9 s).

Principal possibility of real-time low loss optical link between moving objects by means of aberrations cancelling phase conjugation (PC) technique is theoretically analyzed and experimentally verified using photorefractive SBN crystals. Angular tracking rate up to 0.5 degrees per second at 0.2 W light pumping power had been demonstrated in visible. Technical characteristics which are expected for real-time tracking via adaptive PC links are estimated in comparison with conventional electronics tracking systems. It is shown that a combined scheme, which incorporates an additional photorefractive double PC mirror for fine cancelling errors of the basic tracking system, seems to be the most promising one and would result in significant enhancement of a tracking accuracy. PC link between the Earth based multi- channel transmitter and the array of retroreflectors as a passive retranslator which is located at a geostationary orbit and distributes multiplexed signals of all the channels among many users at the Earth is proposed and discussed.

Studying Bi₁₂TiO₂₀ photorefractive fiber-like crystals we experimentally proved that fiber geometry has many advantages compared to the usual bulk samples. Double phase- conjugate mirror with its conversion efficiency up to 8% has been recorded in a wide range of the pump's incidence angles at lambda equals 632.8 nm for 3 mW input light power. Anomalous behavior of the fanning effect time response has been observed in Bi₁₂TiO₂₀ fiber-like samples: the higher external electric field we apply to the fiber the faster response time we get.

Temporal effects of the optical phase conjugation in dispersion-shifted fibers and in semiconductor laser amplifiers are numerically shown. In dispersion-shifted fibers, the frequency chirping is induced in the conjugate pulse by the signal pulse and pump wave through the cross-phase modulation, which increases with the signal power. In semiconductor laser amplifiers, the conjugate pulse has distortion and frequency chirping due to the amplified spontaneous emission noise and the carrier depletion induced by the signal pulse. These effects can be reduced by increasing the pump power. By properly choosing the signal power and pump power, for both conjugators, the optical phase conjugations can be nearly ideal. Finally, the performances of the two conjugators are compared.

In this paper recording possibilities of non-stationary gratings in active medium of photodissociative iodine laser and using four-wave mixing for phase conjugation in its own medium were experimentally investigated for the first time.

This report is to call attention to a very simple class of neural networks (linear associative memories) that can be successfully adapted to data processing in linear adaptive optical trains for wavefront correction.

Hybrid optical/digital laboratory setup that simulates large-scale phase distortions corresponding to various models of atmospheric turbulence is presented. Setup consists of flexible controllable mirror, computer, electronical interface, TV camera and framegrabber. Software for control signals generation is also developed.

Application of high spatial frequency filtration gives the opportunity to increase the efficiency of radiation delivery by coherent adaptive systems and to decrease a number of actual terms in spectral expansion. Modern high-rate technique of wavefront sensing and correction makes it possible to combine the advantages of phase conjugation and multidither modes for middle ranges at horizontal paths.

The sensor based on the unharmonic grating which operates as a set of phase compensators of a wave front curvature is investigated. Applications of the sensor for a real-time measurement semiconductor laser output beam astigmatism via a pumping current and for a lens testing are presented.

Principles of using the methods of adaptive optics in coherent imaging systems are considered. Algorithms of adaptive control of transmitted and received fields were synthesized, which provide the focusing of illumination beam on the observed object and phase distortions correction in direct and return propagation paths under the condition of a priori uncertainty.

We demonstrate the principal possibility of regenerative amplification of laser-injector signal with given phase distribution by a ring reflective amplifier with self-conjugate resonator. Effects of amplifier optical deformation on formation of given wave front during amplification were studied. Frequency locking conditions of interjector-ring amplifier system have been considered.

Peculiarities of constructing adaptive optical systems for forming and transportation of laser radiation through the atmosphere are considered. Results on elaboration and testing of the elements and the adaptive schemes on the special test-bench are given. The results on investigation of real-time compensation of the atmospheric phase disturbances using the adaptive optical train with the heterodyne wavefront analyzer, the electro-optical phase corrector, and the data-processing system based on the neural network are also reported. We analyze possible means of construction of adaptive optical trains to one-channel laser radiators and multi-channel phased systems.