It is suggested that a phase-contrast interferometer can be used in combination with a thin layer of a transparent nonlinear medium in narrowing the angular distribution of a coherent laser beam. An experimental demonstration is reported of a fourfold increase in the axial brightness of a diverging He-Ne laser beam. A cell containing a liquid crystal and an additional layer, which absorded partly the laser radiation and heated the crystal, was used as the nonlinear medium. The experiments confirmed enhancement of the brightness of the phase image in the proposed system.

Considers the performance of a neural-network (NN)-based visual control system with NNs of different types (multilayered perceptrons and Hamming nets). They discuss the possible compensation of disturbances arising in a coherent-optical processor by NN learning. Simulation shows that different NNs have different behaviors for two types of input distorted data: the perceptron NN is more suitable for compensation of optical tract errors while the winner-takes-all NN performs better for noise damaged input patterns.<>

An analysis is made of the interaction of two coherent waves of different intensities in a thin layer of a transparent nonlinear medium. It is shown that such interaction or mixing can amplify the weaker wave without altering its wave front. A report is given of an experimental demonstration on the amplification of a spherical CO2 laser radiation wave by interaction with a high-power spherical wave (with a different radius of curvature) in a thin layer of gaseous SF6. The applications of this effect in correction of wave fronts and enhancement of the intensity in phase images are considered.

An interaction is considered between two coherent waves of different intensities in a thin layer of a transparent nonlinear medium. It is shown that this mixing makes it possible to amplify the weaker wave retaining its wavefront. The amplification has been demonstrated experimentally of a prescribed spherical CO2 laser radiation wave by a high-power spherical wave with a different curvature radius in a thin layer of the SF6 gas. Application is discussed of the mentioned phenomenon in the problems of wavefront correction and amplification of the phase image intensity.

An analysis was made of the possibility of correction of phase distortions of a light beam in a system comprising an interferometer and a nonlinear medium. It is shown that when the beam intensity exceeds a certain threshold value it is possible to eliminate completely the effects of small deformations of the wavefront. In general, such a system reduces the angular distribution in a beam. Experimental evidence is given of the feasibility of correcting a distorted phase front of CO2 laser radiation by passage through a layer of ammonia.

An investigation is made of the characteristic features of self-focusing of radiation in the case of formation of a crater in an opaque medium (metal). It is shown theoretically that a considerable increase in the energy density at the bottom of a crater is possible because of the excitation of whispering gallery waveguide modes in the crater. A self-similar regime of crater formation is considered. A study is made of the influence of the roughness of crater walls on the maximum depth of penetration of metals by laser beams with different polarizations. The results are given of an experimental determination of the distribution of electromagnetic energy in narrow capillary tubes.

An investigation was made of the laws governing the formation of a crater having a high keyhole- penetration parameter in a specimen of poly methylmethacry late under the action of pulseperiodic CO2 laser radiation. It was found that an important part is played in this process by the absorption of the incident radiation in the gaseous phase and also by the excitation of forced acoustic standing vibrations within the crater cavity. The acoustic flow patterns increase the heat flux to the walls of the cavity and produce locally broadened regions. These processes limit the feasibility of attaining high values of the depth-to-diameter ratio of the crater.