B. N. Mavrin

Law of conservation of momentum and rule of mutual exclusion for vibrational excitations in hyper-Raman and Raman spectra of glasses

Abstract The dependences of hyper-Raman and Raman spectra on the scattering angles and polarization are studied in SiO2, TiO2SiO2 and the other oxide glasses. It is found that the vibrational excitations (both polaritons and purely mechanical vibrations) are characterized by well-defined wave vectors in these glasses. The absence of polaritons in the Raman spectra and the band frequency noncoincidence in the hyper-Raman and Raman spectra have allowed us to come to the conclusion that polar modes of glasses were forbidden in the Raman effect (the rule of mutual exclusion). A new approach to the interpretation of vibrational spectra in glasses is suggested. In accordance with this approach the spectra of glasses must consist of two parts: the first one (disordered) is proportional to the density of vibrational states, the second one is crystalline-like and satisfies the selection rules including the law of conservation of momentum for the isotropic medium of the ∞ ∞ m symmetry. The frequencies of the intensity maxima in the hyper-Raman spectra are shown to be related to the crystalline-like part.

Hyper-Raman scattering in the LiNbO3 crystal

Abstract The hyper-Raman spectra in non-centrosvmmetric LiNbO 3 crystal were obtained using the multichannel recording technique. The hyper-Raman cross-section and non-linear susceptibility for the 151 cm -1 band were measured.

Two-phonon hyper-Raman scattering and polariton spectra in rutile crystal

Abstract The first observation of both two-phonon and polariton hyper-Raman scattering in rutile crystal is reported. The effect of two-phonon states on A u -polariton dispersion has been found.

Longitudinal-transverse splitting of dipole modes in hyper-Raman scattering spectra of liquid CCl4

Abstract The first observation of the longitudinal-transverse splitting of dipole vibrations in liquid CCl 4 is reported. Using the hyper-Raman scattering technique, we have obtained the spectra of transverse (313, 760 and 782 cm -1 ) and longitudinal (≁770 and 800 cm -1 ) modes in CCl 4 . Polarization analysis is shown to be used to distinguish longitudinal and transverse modes of dipole vibrations in hyper-Raman spectra.

Polariton fermi-resonance in hyper-raman spectra of a calcite crystal

Abstract Fermi-resonance of the transverse Eu-polariton with two phonon v1 + v3 and v3 + v3 zones in a calcite crystal was studied. The experimental data were found to be in a good agreement with the present-day theoretical model of the polariton Fermi-resonance.

A study of the nonsymmetry of the hyper-Raman tensor in α-quartz using two-frequency excitation

Abstract The first observation of the hyper-Raman scattering excited by two laser beams ωi1 and ωi2 is reported. Using the two-frequency excitation of the hyper-Raman spectra of α-quartz, the polarized spectra are obtained and effects of the nonsymmetry of the hyper-Raman tensor are studied. It is shown that the contribution of a nonsymmetric part is essential although the frequencies of the exciting and scattered light are far from the electron absorption bands.