ИСТИНА

Localized vibrations of nanoparticles in gigahertz and near terahertz range have been observed in suspensions of different nanoparticles under nanosecond laser pulses excitation. For excitation we used ruby laser nanosecond pulses (λ = 694,3 nm, τ = 20 ns, Emax = 0.3 J, Δν = 0.015 cm-1). Laser light scattering by nanoparticles acoustic vibrations is known as low-frequency Raman scattering (LFRS). In our case interaction of two fields (weak LFRS and strong laser) with nanoparticles vibrations produces stimulated low-frequency Raman scattering (SLFRS). SLFRS propagates in forward and backward directions with divergence and linewidth values near to the corresponding values of the exciting light. High conversion efficiency of the exciting light into SLFRS in nanoparticles suspensions (10 - 20 percent) is evidence of intense excitation of coherent acoustic vibrations. Frequency shifts of SLFRS components depend on the sample material and nanoparticles dimensions and correspond to the eigenvalues of nanoparticles vibrations frequencies, lying in GHz and near THz range. Frequency shift is inversely proportional to the average nanoparticle diameter. Frequency shifts of the SLFRS first Stokes component in the samples studied have been measured with the help of Fabri-Perot interferometers with different dispersion range and were from 6 GHz to 0.435 THz depending on the sample properties. Nanoparticles size distribution in suspensions was measured by the dynamic light scattering method (DLS) by the analyzer Zetasizer Nano ZS. Nanoparticles images have been obtained with the help of scanning electron microscopy and high resolution transmission microscopy methods. The effect can be used as a source of biharmonic pumping for numerous applications in different fields of science and technology. With its help it is possible to affect biological nanoobjects or to identify them and to realize nanoparticle size measuring in real time, for instance, in aerosoles of different nature. Work is supported by Russian Foundation for Basic Research Grant 12-03-00396-a.