A. I. Sokolovskaya

Wavefront reconstruction (conjugation) by stimulated scatterings: A review

In this paper, we give review of our work on the holographic image reconstruction of the volume object, illuminated by giant laser pulses of nano- and picosecond duration, and of its Fourier spectrum which has been observed experimentally in Raman, Brillouin, and Rayleigh stimulated scatterings. Image reconstruction laws have been investigated. Wavefront conjugation with transformation, obeying holography principles, has been shown to take place at the backward SRS. A physical model of the phenomenon is given. The diffraction efficiency of dynamic holograms in the stimulated scatterings has been measured. The possibility of the light beams spatial structure conversion at the stimulated scatterings has been experimentally shown.

Backward stimulated Raman scattering in water and water solutions

12 Energetical and spectral characteristics of backward stimulated Raman scattering (BSRS) in water and water solutions of organic liquids (acetone, benzene, ethanol, cyclohexane) at different excitation conditions have been experimentally investigated. Maximum conversion efficiency of laser light into BSRS wave was about 40%. For picosecond range experimental results and calculations are presented showing the BSRS intensity as a function of the main experimental parameters concerning the geometry of excitation and the exciting intensity. Thus its possible to forecast the best experimental set-up in term of BSRS efficiencies and to estimate the minimum length of water necessary to detect BSRS. Competition with other scatterings is observed. In nanosecond range simultaneously with BSRS stimulated Brillouin scattering has been excited. Possible applications are discussed.

Statistical properties of SRS excited in acetone

Experimental investigations of the energetical, spatial and statistical properties of stimulated Raman scattering (SRS) pulses, excited in acetone by picosecond laser pulses, are presented. The properties of the SRS pulses propagating in the forward direction and propagating in the backward direction are compared. Changing the geometrical and energetical conditions of excitation one can change the properties of SRS pulses in proper way.

Nonlinear optical systems for image processing and complex field monitoring

Nonlinear optical systems are presented, giving possibility to change complex light fields characteristics with the aim of image processing on the base of nonlinear optical effects, such as stimulated scatterings of light, two-photon excited luminescence, Kerr-effect etc. These systems allow to perform image processing, changing characteristics of the complex light field, forming the image. For instance, we can change image contrast from that of initial image to the contrast inversion. Its possible also to visualize phase and low-absorbing objects, phase inhomogeneities in transparent materials, thickness variations of low-absorbing layers and roughness of reflecting surfaces. Thus, these methods can find wide applications in materials technologies monitoring, biology and medicine. Image processing is performed in real-time scale, which permits to avoid influence of effects, connected with light beam propagating in materials, and to study quick processes.

Stimulated scattering of light in thin layers of active materials near the surface

Experimental investigations of the object image reconstruction by stimulated scatterings (SS) and SS energetical properties have been realized in this layers of different nonlinear materials in picosecond and nanosecond range as a function of thickness. Sharp SS wave intensity enhancement has been found.

Energetic characteristics of two-photon excited luminescence in organic polycrystals

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.

Some Properties of Stimulated Raman Scattering Excited by Picosecond Light Pulses

For decision of some practical tasks it is interesting to get pulses of stimulated Raman scattering (SRS) radiation with good characteristics: high spatial coherency, the small divergence of beam etc. In nanosecond range of excitation it can be reached by selecting of suitable geometry of the active medium illumination. At the picosecond range the influence of geometry of illumination on the SRS characteristics is not studied well. In work [1] the experimental investigations of SRS energy and space characteristics at picosecond regime of excitation have been carried out. The parallel laser beam was used for excitation of SRS in number of liquids. It was shown that in spite of the good stability of the laser energy (∼10%) the fluctuations of SRS pulses energy were rather large (till 100%). Statistic of backward SRS was independent upon the value of the active medium length. The divergency of SRS-beam was measured to be ≈100 times more than the laser beam divergency. In cross-sections of SRS-beams there were many maximums of intensity, distributed in a random way.

Spatial frequency filtering on the basis of the nonlinear optics phenomena

Different schemes for spatial frequency filtering are described. The possibility is shown to visualize phase objects images and to achieve increase or inversion o contrast oC the amplitude objects images.

Image processing in real-time on the basis of nonlinear phenomena in condensed materials

New methods of light field conversion and image processing are proposed on the basis of two-photon absorption, high-frequency Kerr- effect and different types of stimulated scatterings in condensed materials.