Stimulated low-frequency Raman scattering (SLFRS) spectrum in dimethylformamide (DMF) was registered in the range from 0.1 to 1 cm-1. SLFRS is a result of the laser pulses interaction with acoustic oscillations of the associates, therefore knowledge of the SLFRS frequency shifts (and consequently associates eigenvibrations frequencies) gives possibility to estimate the size of DMF associates. Scattering was excited by pulses of a ruby laser with a narrow spectral line and recorded by Fabri-Perot interferometers. In the scattering spectrum SLFRS component was recorded with a frequency shift of 0.33 cm–1 (10 GHz), which corresponds to the size of associates of about 150 nm. Simultaneously with the SLFRS, stimulated Brillouin scattering was recorded in the backward scattering spectrum.
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.
The low-frequency acoustic mode in nanoparticles of different nature in aqueous suspension has been studied by stimulated low-frequency Raman scattering (SLFRS). Nanoparticles investigated (CuO, Ag, Au, ZnS) had different dimensions and different vibrational properties. Synthesis of cupric oxide nanoparticles in acoustoplasma discharge is described in details. SLFRS has been excited by nanosecond pulses of ruby laser. Spectra of the scattered light had been registered with the help of Fabry-Perot interferometer. SLFRS conversion efficiency, threshold and frequency shift of the scattered light are measured.
Luminescence of nanomaterials in green-blue range, anti-Stokes with respect to the exciting ruby laser pulses, is studied at different temperatures. Both high-ordered systems and random materials have been used as samples. Spectral and temporal characteristics of the luminescence have been measured. Two types of temporal behavior have been found out depend on temperature. Long luminescence (up to few seconds) under nanosecond excitation has been shown to exist only at the temperatures below the definite threshold, which was found to be 110 K.
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.
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.
In the present work the results of the experimental investigations of the stimulated Rayleigh-wing scattering (SRWS) spectral, energetical and spatial properties are presented. SRWS was excited by single pulse of the Nd:YAG modelocked laser second harmonic. Scattering propagating in the direction opposite to the initial laser light was investigated. Acetone and water have been used as active materials. Experiments have been performed under different geometrical and energetical conditions of excitation. The transformation of SRWS spectrum in different excitation conditions has been studied. The existance of the two sharp lines in the SRWS spectrum has been found at some experimental conditions of excitation with frequency shift in the range of ~20 cm-1. Transformation of this two-lines spectrum into one line spectrum was experimentally investigated as a function ofthe excitation geometry and initial laser pulse energy. Four-photon processes, leading to this effect, are considered. Spatial structure of SRWS at the same conditions of excitation has been studied. Possible applications of the SRWS for image processing according to the results on the SRWS spatial structure investigations are discussed.
The problem of image processing by nonlinear phenomena at the process of stimulated scattering of light simultaneously at different wavelengths is investigated. The influence of nonlinear effects and excitation conditions (the initial light intensity and excitation geometry) is considered. Experimental results and theoretical model of the image reconstruction are presented.
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.
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 it's 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.
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 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. It's 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.
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.
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.
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.
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