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.
Transmission spectra of holographic sensors based on the Denisyuk holograms with silver nanograins embedded in the polymer matrix are investigated. It is necessary for the determination of the operation mode and of optical parameters of the sensors. The spectra have a narrow Bragg dip against a background decreasing with decreasing the wavelength. Three parameters of this dip determine the operating mode of the sensor. To calculate them, it is necessary to know 3 background parameters. All the parameters are calculated from fitting curves based on the formula proposed earlier which approximates the experimental spectrum quite well. It turns out that the spectral interval chosen for fitting is important and a solution exists not over any interval. When it exists, the parameters of the dip (the main goal of our work) are determined with a good accuracy. As for the optical parameters of the background, those associated with light scattering and with absorption seem to be strongly related. Changing the fitting interval leads to a correlated change of the values of parameters, sometimes considerably. Nevertheless, the fitting function approximates the experimental spectrum quite well and the accuracy of determining the Bragg dip is high.
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.
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