We suggest a new way to compensate for the thermal lensing effect in the mid-power solid-state lasers. This can be done by the use of a liquid-crystal adaptive lens with optically controlled focal length (optically addressed lens -- OAL) which is a modification of the modal liquid crystal lens (MLCL) which has recently been suggested and successfully implemented. The phase shift introduced by OAL into the transmitted light wave is theoretically shown to correspond to a converging lens whose focal length depends on the light intensity distribution across the aperture. OAL implements an intra-cavity optical feedback, which can effectively compensate for the laser beam defocus resulted from the emerging thermal lensing. For various types of resonators the beam stability is improved by the use of OAL. Correction becomes more effective if the OAL is positioned close to the laser rod.

Static and dynamic numerical models of electro-optical characteristics of nematics are presented. A numerical model is used for the optimization of phase delay distribution in modal LC lenses. The dynamic control mode for modal LC lenses is simulated. The results are in a good agreement with experiment.

The paper presents results on research of tunable acousto- optic filters operating in ultraviolet, visible and infrared regions of spectrum. High spectral and spatial resolution, perfect diffraction efficiency and low driving power provide application of the filters in optics and spectroscopy as well as in optical information processing and laser technology. Precise and efficient electronic control of laser light intensity and fast electronic tuning of lasing wavelength was executed by means of collinear acousto-optic devices. Application of the collinear filters as selectors of arbitrary polarized optical signals in modern WDM waveguide communication lines has also demonstrated high capabilities of the acousto-optic instruments. Experiments with the acousto- optic devices on base of the wide-angular geometry of interaction confirmed the unique possibility to regulate spatial structure of convergent laser beams and optical rays forming images.

The results of studying the electro-optical sensitivity of industrial glasses are presented, and it is shown that Kerr constant, B, of them does not exceed 10^-15 m/V². An approach to the choice of compositions of the glasses of high Kerr sensitivity is developed, and experimental sodium- niobium-silicate glasses with B > 10^-14 m/V² have been designed and formed. The approach is based on the hypothesis of 'crystalline motifs' (structural inhomogenities responsible for electro-optical sensitivity of the glasses), which are the ordered regions (several coordination spheres) with the crystal-like structure. When heat-treated the designed glasses crystallize, with the phase precipitated being NaNbO₃ microcrystals. Temporal-thermal conditions of the glass crystallization to form a transparent glass-ceramics with B approximately equal 10^-12 m/V² have been found. It has been also shown that such glass-ceramics can be produced by high-temperature alkaline ion exchange. A low- temperature silver ion exchange in the designed glasses and glass-ceramics has been studied and optical waveguides supporting from 1 to 50 modes have been formed. In these waveguides the index variation equal to 0.15 is achieved.

The operation of various designs of a Faraday isolator at high average power with an arbitrary orientation of a cubic magneto-optical crystal is studied theoretically. It is shown that in different Faraday isolator designs, different crystal orientations may be optimal from the standpoint of isolation. Thermo-optic and photoelastic constants for terbium gallium garnet crystals grown by different producers were measured. Measurements of self-induced depolarization were made for various orientations of crystallographic axes. The measurements are in good agreement with theoretical predictions. Based on the obtained results it is possible to choose such crystal orientation for Faraday isolators which is optimal from the standpoint of isolation at high average powers.

Theoretical analysis of spectral properties of volume phase gratings with high-reflective boundaries has been carried out for both transmission and reflection gratings. High Fresnel reflection at grating boundaries was shown can result in radical changing diffraction properties and significant increasing spectral selectivity in comparison to well-known Bragg selectivity. Structures considered can be of interest in developing demultiplexers for WDM optical networks, selective absorbers of laser power and other photonics devices.

Optimization of the grating structure parameters at the working wavelength 1.06 (mu) is made on the basis of the calculation method for the diffraction gratings with nonequidistant coatings. The comparison of the experimental and calculation data has revealed the considerable smoothing of an initial grating relief by evaporation of multi-layered coating. On the basis of theoretical estimations the untraditional area of optimum layer thickness is suggested. The theoretical diffraction efficiency for this area at real relief smoothing is 96%.

This work analyzes the influence of phase distortions caused by variable-reflectivity multilayer dielectric mirrors on the spatial and energetic characteristics of the output radiation of lasers with unstable and plane-parallel resonators. The phase distortion of such mirrors has been considered in dependence on design parameters of optical coating. Some application peculiarities of soft-edge mirrors for the Cassegrain and Fabry-Perot resonators of lasers are discussed. The work represents some recommendations for the mirror design that ensures the optimal output laser beam characteristics.

The new optical effect of a diffractive multifocal focussing of radiation, predicted by the theory, on a bicomponent diffraction system with small Fresnel numbers, consisting of two plane screens with circular apertures on a given optical axes, is confirmed experimentally. Is shown, that the diffraction picture in the focal planes of such system represents the circular nonlocal bands of the Fresnel zones with a bright narrow peak at the center, whose intensity in the experiment can exceed by six to ten times the value of the incident plane wave intensity. Experimentally is established, that the diffractive multifocal focusing of a radiation on a real screens with axial circular apertures, whose diameters exceed a radiation wavelength, is insensitive to the 'rough' external conditions: to a thickness of screens, to the irregularities of edges and non-ideal form of apertures, to a heterogeneity of initial distribution of an incident wave intensity, to changes in the medium of the wave propagation.

The phase distortion's influence on the radial luminosity of the laser radiation in distant zone occurred in mirrors with radial reflection coefficient has been investigated. It was shown that the radial luminosity diminished 1.5 - 2 times in comparison with mirrors characterized by constant or having spherical front radial phase's distribution along a mirror coating. New methods of radial phase distortion compensation are suggested for increasing of the radial luminosity of the phase front: (1) a deposition of additional layers with required radial thickness function, (2) a special choice of reflective coating's structure. Examples of the synthesis and practical making of output mirrors of CO₂-laser's unstable resonators are demonstrated. Due to the mirrors with phase distortion compensation of laser radiation the radial luminosity increased 3 time in comparison with the usual mirrors.

The results of theoretical and experimental studies on photodynamics and mechanism of nonlinear optical processes, responsible for optical limiting of power radiation in the wavelength range from 0.3 to 1.3 microns, are presented. Peculiarities in the mechanisms of optical limiting for different fullerene-containing matrices, including solutions, solid-state and polymer systems, are shown.

We present the results of chemical development and optical investigation of the extraordinarily large photorefractive effect in the new polymer nanocomposites. The composites are composed of poly(ethynylene)arylenesilanes as optical chromophores, poly(9-vinylcarbazole) as photoconductor, N- ethylcarbazole and phenyltrimethoxysilane as plasticizer, and C₇₀ and C₆₀ fullerenes as charge generators. The magnitude of the change in photorefractive index and its origin, and temporal behavior were studied at 633 nm by a variety of nonlinear optical techniques, including nonlinear lens method, four-wave mixing and two-beam coupling. The relaxation time of the photorefractive index changed in a range from a few seconds to tens of minutes at changing beam intensity.

High contrast fast switch of transmission in optical channels of iodine laser facilities is supplied with liquid bleachable dye cells. New dye cell designs which combine the functions of an optical shutter and a soft diaphragm are considered. 70 - 100 mm in diameter cell-apodizers of two types (with profiled absorbing liquid layer and profiled transmission of optical components) are developed. Cells with profiled absorbing layer contain meniscus-lens spacer, which cancels the optical power of the device. Cells with plane parallel liquid layer contain windows with profiled transmission. The laser shot-blasted technology for the surface and volume processing of the cell windows was used. For approximately equals 1% initial transmission at the laser beam axis the cells' bleaching reaches 70%, and the contrast ratio of the cells' transmission profile from the beam axis to the periphery may reach K approximately equals 1000. The application of high-aperture cell apodizers in the iodine laser optical channel will make it possible to eliminate the influence on the beam profile of the disturbances in a gaseous active medium at the periphery of amplifier modules caused by the open discharge used for pumping, and to form a smoothed spatial profile of the laser beam.

Under the Raman-Nath diffraction conditions the thin holographic gratings have been recorded in a promising class of (pi) -conjugate organic materials based on polyimide and 2- cyclooctylamino-5-nitropyridine. The drastic change of refractive index has been observed in the systems doped with fullerene C₇₀. The results have been explained both by laser-induced conformational transformations of organic materials and by their spectral and thermal properties.

The contribution of light induced scattering to nonlinear optical limiting is theoretically and experimentally investigated. It is shown that light induced scattering is caused by fine-scale (1 divided by 10 micrometer) inhomogeneities formation, very low (comparable to spontaneous noise) laser beam inhomogeneities can evolve into light induced scattering. The numerical modeling of scattered radiation angular distribution and laser radiation attenuation in optical limiters was performed. The modeling results were compared with the experimental ones.

The optical limiting of the laser radiation over visible and IR ranges in organic material based on polyimide has been studied. The role of the donor-acceptor interaction mechanism in manifestation of organic molecules nonlinear-optical properties has been established. The fullerene-doped photosensitive polyimide structures have been determined to be effective optical limiting materials for attenuating a power density of more than 2 - 4 J(DOT)cm^-2.

For the first time three-wave interaction of picosecond pulses was investigated as difference frequency generation with Ag- GaSe₂ crystal. Group velocities and radiation absorption were taken into account during spectral analysis realization. Calculations were executed for CO₂ laser parameters: 100 divided by 5 ps, 15 divided by 150 GW/cm². Spectral characteristics and pulse power versus crystal length are represented for difference wavelength 800.5 micrometer.

In the work consideration was given to investigation into the spectroscopic and nonlinear optical properties of photorefractive semiconductor cadmium telluride crystals doped with vanadium, ferrum and titanium. Introduction of dopants was required to produce an impurity absorption band in the near IR region and enhance the photorefractive properties. Two methods have been used for the production of doped crystals: diffused post-growth doping and growth of doped crystals from melt. Nonlinear optical properties of samples were studied at the wavelength of 1.06 micrometer in a four-wave mixing scheme. Maximum diffraction efficiency was revealed for the convergence angle of light beams approximating 8 degree, with the grating period of 7 micrometer and was equal to 2%. The dynamic grating lifetime was about 0.2 microseconds.

Investigations of resonant spectral structures of four wave mixing (FWM) in molecular sodium are presented. For a double- (Lambda) configuration with strong-weak-strong-weak fields, split components in FWM spectra induced by the strong pump fields are observed. It is shown, that the split components merge into a single peak for a certain ratio of the strong field intensities. A strong correlation between the level splitting effect and saturation behavior of the FWM-signal is experimentally demonstrated.

Dramatic reduction of the number of oscillating modes in CW and pulsed lasers has been observed using a photorefractive crystal placed inside the cavity. Reflective Bragg gratings recorded by the standing waves inside the crystal act with the output coupler as a self-adapted Fabry-Perot filter. Its spectral characteristics enhance mode competitions which can lead to a single mode operation.

Two-frequency solid-state lasers are shown to provide beat notes at frequencies from dc to the THz range with continuous tunability, high spectral purity and 100% modulation depth. Depending on the desired range, one- and two-axis cavities are built. Applications of such lasers as a local oscillator in radio-over-fiber communication systems or as a quasi-absolute tunable frequency source for highly-dense wavelength division multiplexed networks are emphasized.

Experimental investigations of radiation parameters of 2D arrays of waveguide CO₂ lasers synchronized by in-cavity spatial filter method are carried out. Phase locked regime in a system of two ring waveguide CO₂ lasers with a common cavity and unidirectional lazing was achieved and investigated.

We have studied, both theoretically and experimentally, the doubling of topological charge of dislocations of Bessel light beams, transfer of a dislocation to a second harmonic radiation without change of its topological charge, and annihilation of screw dislocations of the opposite sign.

We present a new scheme of optical resonator for production of Bessel and Bessel-Gauss beams. This resonator, employing only spherical mirrors and axicons, does not contain any complicated optical elements. Analytical expressions relating parameters of resonator and characteristics of its modes are obtained and analyzed. Diffraction energy losses are calculated with Fox-Li algorithm, and modal discrimination is studied.

A new method for obtaining high-order Bessel light beams has been developed and proved theoretically and experimentally. It is based on the phenomenon of transformation of circularly polarized light beam passing through biaxial crystal along its binormal. The method can provide conversion of input Gaussian beam into Bessel beam with an almost 100% efficiency. Besides this method can be used to convert high-intensity laser beams. The light field having the cross distribution in the form of spiral is obtained from the first order Bessel light beams. A possibility of formation of the zeroth and the first order Bessel light beam from Gaussian light beam in biaxial crystal without axicon is investigated theoretically.

Presented is a stable single-frequency master-oscillator on the basis of a pulsed dye jet laser for powerful isotope separation systems. In a simple GIG resonator without prism expanders, we obtained 170-mW single-frequency output power with an open beam pump and up to 100 mW with a fiber-guided pump. The application of a frequency stabilization system brought the short-term stability down to 50 MHz/s (at pulse duration 8 ns, 15-kHz repetition rate) and the long-term stability down to 120 MHz/hour. A smooth frequency scan within an 8 GHz region (and wider) was achieved on the basis of pivot method with newly implemented components.

We report on a CW single-frequency dye laser with a 1-W threshold power. Output power of the laser working on the Rhodamine 19 dye was 100 mW out of 2.4 W of the argon ion pump. Smooth frequency scanning in a 20-GHz region with up to 20-GHz/s rate was implemented in a linear dye laser cavity. A special resonator auto-adjustment system with internal reference features the short-term radiation linewidth down to 3 MHz/s and long-term stability level of 150 MHz/hour without any external frequency stabilization systems. Explained are arrangements of original execution units included into the laser control system. The control system's features are discussed.

The evolution of autocorrelation function observed at the 50 ns resolution for prelase oscillations of actively mode-locked laser evidences that an effective and fast pulse shortening begins when the intracavity radiation intensity attains the saturation level. Pulse duration decrease down to 70 - 75 ps value during 10 cavity roundtrips and further remains unchangeable and independent on the ultrashort pulse energy.

The dependence of output parameters of a Ti³⁺:Al₂O₃ tunable laser (an efficiency, build-up time, jitter, etc.) on the temporal delay between pump pulses of a Q- Switched double pulse Nd³⁺:YAG laser has been investigated. The advantages of double pulse pumping of the Ti:Sapphire oscillator has been demonstrated, experimentally. New methods of output characteristics control for tunable Ti:Sapphire lasers have been proposed.

Using the most complete in literature physical model of the non-steady-state stimulated Brillouin scattering (SBS), the numerical study is carried out of phase conjugation (PC) in the SBS-mirror that consists of an angular selector of Stokes radiation, an ordered raster of small lenses, a main focusing lens, and an SBS-cell. The ordered raster with controlled varying of its parameters allows to perform the effective angular filtering of non-conjugated Stokes component, to reduce the local light loads, and to avoid the competitive nonlinear effects. An optimal configuration of such SBS-mirror has been determined. It has the unique properties as compared with the current SBS-mirrors. It fixedly yields the PC quality that is near to an ideal (the PC coefficient is about of or more than 95%) at the selector transmittance 50 - 70% and any level of SBS saturation, i.e. any reflection coefficient. In the SBS-mirrors of different types the high PC quality in the focused beams takes place at the high reflection coefficients only that is difficult to realize as a rule. The experimental data obtained at a Nd laser facility show the validity of the simulation results. The developed conception of SBS-mirror with unique properties can be applied for the improvement of wide class of industrial lasers.

The powerful neodymium lasers with the self-phase-conjugation (SPC) and passive Q-swither are submitted. It is shown, that the application of a LiF:F₂^- crystal as Q-swither and SPC-mirror simultaneously, and also a Sagnac interferometer as end reflector of the cavity allows to increase efficiency and quality SPC-radiation. High power and spatial laser characteristics are obtained: Nd:YAG laser -- 114 W average power at 0.5 mrad beam divergence; Nd:YAP laser -- 51 W average power at 1.2 mrad beam divergence; Nd:Glass laser -- 18 J in pulse train at 1 mrad beam divergence.

We have studied both experimentally and numerically the role of resonant refractive index gratings in a self-pumped phase conjugate mirror based on an Nd:YAG amplifier with nonreciprocal feedback loop. In experiment the generation of the phase-conjugating laser was delayed with respect to recording of a holographic nonlinear mirror by an external beam. An increase in the phase-conjugate reflectivity at a delay time of about 3 microseconds was measured. The numerical calculation confirmed the additional contribution of the resonant refractive-index grating, which is formed in the pumped Nd:YAG crystal due to excitation of a higher-lying level of Nd³⁺ ions, to efficiency of phase conjugation.

The transverse beam profile of solid-state lasers is a key issue for determining its propagation properties. Herein, we address laser beam distortions caused by thermal lensing and birefringence. For the simulations a finite difference method is used for the description of beam propagation problems. The method is an improved approach to the solution of the wave equation in paraxial approximation. Provided that steady-state conditions prevail, in comparison with the Fresnel-Kirchhoff integral description this method allows for a fully 3 D treatment of the aforementioned laser-optical phenomena.

In this review some results on spiral beam optics are considered. Spiral beams keep their intensity structure unchanged under propagation except its scale and rotation. Some theoretically calculated spiral beams and the ways of their experimental constructing are presented. A comparison between an example of nonrotating but structurally stable beam and a corresponding spiral beam is performed.

The real time control of the rotation rate of a microscopic particle trapped in a focused laser beam by mean of polarization ellipticity of laser radiation has been studied. The ellipticity change was carried out with the modulator using orientational S-effect in nematic liquid crystals. The dependence of the particle rotation speed on the state of polarization ellipticity was determined. The calculation of an angular momentum of rotation per a unit of energy of the light field is shown.

We describe an optical image restoration by using holographic filtering and photorefractive four-wave mixing. A beam generated by four-wave mixing, that is, the phase conjugate beam, reads a hologram recorded by a blurred image and blur function, where the four-wave mixing process is influenced by an erase beam which has the information of the blur function. We calculate the generation efficiency of the phase conjugate beam and show that the amplitude of the phase conjugate beam can be inversely proportional to the intensity of the erase beam. We also simulate the image restoration by preparing sample images and show that the blur effect can be removed from the distorted image by this method.

We demonstrate how to correct odd-order aberrations (tilt, coma, etc.) of the imaging system on the basis of information containing in the phase transfer function. For earth- observation systems this information can be obtained just by accumulation of the detected images, without source of the reference beam or wavefront detector. This technique is beneficial for elaborating robust equipment for long-term operation in autonomous conditions.

The dynamic holography is considered as the most perspective technique of correction for dynamic aberrations of large- aperture optical elements when operating in near IR range. The use of fluorocarbon Flourinert FC-72, characterized by Brillouin nonlinearity, for recording the dynamic hologram has been demonstrated experimentally. Resonant enhancement of the hologram's diffraction efficiency resulting in 10 times growth has been shown. Diffraction efficiency over 50% has been obtained. Different behavior of diffraction efficiency in dependence on intensity of recording beams and length of nonlinear medium has been shown. Capability of correction of laser beam distortions as well as dynamic behavior of recorded hologram have been tested. The random phase distortions bringing about 20 times increase of the laser beam divergence have been corrected resulting in near-diffraction quality of a point object image. It has been shown that lifetime of the hologram does not exceed 10^-9 sec. Perspective of the use of Brillouin enhanced dynamic holography for nonlinear compensation of optical aberrations has been presented.

Conventional adaptive optics systems using a single wavefront corrector suffer from a limited field of view. Multi-conjugate adaptive optics use two or more corrector to improve off-axis correction. We describe an experimental system which simulates dual-layer turbulence, and present results using a single corrector showing anisoplanatic effects. Future experiments using a second corrector are also discussed.

Interferometric radar technique is an important tool for a surface topography reconstruction of optically rough surfaces. Spectral interferometric radar is based on optical interference phenomenon that is observed in the form of the periodical modulation of broadband spectrum at the output of interferometer. Group optical path difference of interfering light waves corresponding to the distance from the surface to be measured is characterized by the phase function or fringe frequency of the spectral modulated interferogram. To measure fringe frequency a noise-immune recurrence non-linear filtering method was used where interferometric data are assumed to be a series of samples of the spectral interferometric signal defined by a known model. It is predicted the signal value from previous step of discretization to the next step. The prediction error is used for signal parameters correction. Recurrence non-linear filtering generally gives the optimal dynamic estimate of the phase function, frequency and visibility maximum position of the interferogram. Method was verified experimentally with application to the analysis of the spectral modulated interferograms inherent to Michelson interferometer excited by low-coherent source with a subsequent spectrometer.

Possibilities are considered of noisy signals processing by four-wave mixing (FWM) of laser radiation in a two-level medium with taking into account of the combined influence of spatial phase matching, nonlinear response inertia, and phase cross-modulation. Regularities of time behavior transformation of randomly modulated signal are collated with particularities of FWM-reflectivity of deterministic pulses. Results are discussed of correlation analysis of FWM with partaking in a random way amplitude (or phase) modulated signals.

A noise-immune method of phase retrieval of single moire interferometric fringe pattern is presented and discussed. The method is shown to provide accurate recovering of the phase information by combined method based on modification of local histogram of the fringe intensity and two dimensional Fourier transform of enhanced moire fringe pattern. The principle of the method is described and the experimental results of moire interferometric measurements with submicron sensitivity of the in-plane displacement fields of thick carbon fiber/PEEK composite laminates are presented as example of application of the technique.

The approach is suggested, which permits more full description of correlation responses of thin holograms with superposed registration on the basis of account of contributions from all the nonlinear with respect to the recorded object fields inter- and cross-modulation diffraction structures. Based on this approach, from the common point of view the associative reconstruction of information by the thin quadratic off-axis hologram and the linear off-axis hologram -- phase-conjugate mirror system was considered.

We report semi-classical numeric simulations of the quantum spatial fluctuations in parametric amplification of images limited by the shot noise. Noiseless amplification of images is demonstrated by the use of a degenerate type 2 phase sensitive amplifier.

We consider the influence of the inertial component of the optical fiber response on the cnoidal waves propagation dynamic and analyze the dependence of the self-bending parameter on the degree of the temporal localization of the wave energy. We have shown that for the case of the cn-wave the role of self-bending effects increases (and for the case of the dn-wave decreases) with growth of degree of localization.

We consider the propagation of the laser beam near the interface between the linear dielectric and photorefractive medium with drift and diffusion nonlinearity. We demonstrated the possibility of the surface waves formation, found the profiles of such surface modes and investigated waveguiding properties of the dielectric -- photorefractive medium boundary. The effective particle theory was used to derive an ordinary differential equation that describes the beam center trajectory during the reflection from the interface.

The control implies a slow small harmonic modulation with properly chosen frequency and amplitude to the available laser parameter, for example, to the loss, pumping, or cavity detuning. This type of the control results in exiting phenomena such as nonlinear parametric resonances, a shift of bifurcation points (period-doubling and saddle-node), deformation of boundaries of attractors and even their destruction.

The delayed feedback control of the chaotic dynamics of the optoelectronic system with a laser diode is analyzed and experimental results are presented. The degree of the chaos suppression and suppression time were measured for three cases differing in the functional dependence of the control signal on the change of the laser output power: proportional, exponential or combined. It was found that the degree of the chaos suppression did not depend much on the control technique. The suppression time was different in all cases and in the third one it was minimal.