Anna D. Kudryavtseva

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.

Stimulated globular scattering and photonic flame effect : new nonlinear optics phenomena

Novel nonlinear optical phenomena - photonic flame effect (PFE) and stimulated globular scattering (SGS) are discussed.PFE consisted in the appearance of the few seconds duration emission in blue-green spectral range under 20 ns ruby laser pulse excitation and simultaneous excitation of several spatially separated synthetic opal crystalls situated on the Cu plate. SGS was observed both in forward and backward directions. Spectral and energetical SGS characteristics were measured.Novel nonlinear optical effects - photonic flame effect (PFE)1,2 and stimulated globular scattering (SGS)3 - have been discovered. SGS was observed both in forward and backward direction. Pure opal crystal, consisting of the close-packed SiO2 globules with diameter 200 nm, and crystal with pores, filled with molecular liquid, have been studied. Two Stokes components, shifted from the exciting light frequency by 0.4 - 0.6 cm-1, have been observed in SGS. Photonic flame effect consisted in the appearance of the few seconds duration emission in blue-green spectral range under 20 ns ruby laser pulse excitation.

Stimulated light scatterings in submicron single crystal diamond films implanted with light ions

Stimulated low frequency Raman scattering (SLFRS) in submicron single-crystal diamond films (SCD) with a graphitized layer built-in is investigated. The value of SLFRS frequency shift lies in gigahertz range (8.4-9.3 GHz) and shows the morphological dependence (inverse dependence on the thicknesses of SCD layers). Experimentally estimated SLFRS conversion efficiency and threshold evidence about the coherent phonon mode excitation in submicron SCDs as a result of nonlinear interaction of high-power laser wave with an eigen vibration of nanosized graphitized layer built-in.

Stimulated globular scattering in photonic crystals

Novel nonlinear optical effect - stimulated globular scattering (SOS) - was discovered. SGS was observed both in forward and backward direction. Pure opal crystal consisting of the close-packed Si02 globes with diameter 200 nm, and crystal with pores filled with molecular liquid have been studied. Two Stokes components, shifted from the exciting light frequency by 0.4 - 0.6 cm-1 have been observed.

Spatial and temporal characteristics of stimulated scatterings in water

Spatial, temporal, and spectral characteristics of stimulated scatterings (SS) of light, excited in water, have been investigated both in nano- and picosecond range in different experimental conditions and compared with the analogous properties in other liquids. The results can give important information about the structure of water, its purity, and additions, which may lead to its pollution. Conditions have been defined for stimulated excitation of SS in one spatial mode and with maximum pulse conversion. Stimulated scatterings of light can be used for water quality control, which may be fulfilled in a very short time, and for information processing: amplitude-phase structure of complex light fields may be registered in water as dynamic hologram and reconstructed in a real-time scale.

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.