Light scattering by extraordinarily polarized polaritons

The objective of this work is to investigate how the anisotropy of the inte raction between dipole-active vibrations of a crystal lattice and infrared electromagnetic waves is manifested in the spontaneous parametric light sca ttering spectra of polaritons (Raman scattering by small angles). The case where scattering occurs by extraordinarily polarized polaritons-quasipartic les formed as a result of the coupling of the wave polarized in the symmetr y plane of a biaxial crystal simultaneously with two phonons possessing ort hogonal dipolar moments-is studied. A series of spectra of equilibrium fluc tuations of the electromagnetic (infrared) field, each of which represents an intensity distribution in frequency-wave number coordinates for a fixed direction of the wave vector, are constructed on the basis of a scattering model that takes account of the tensor character of the permittivity and th e quadratic and cubic susceptibilities of the crystal. Analysis of the comp uted spectra identified the basic laws and dependences which are determined by the anisotropy of the electromagnetic susceptibilities of various order s and made it possible to explain previous experimental results which canno t be interpreted on the basis of the generally accepted model of transverse ly polarized polaritons. A method is proposed for determining the contribut ions of the dipole-active vibrations of the crystal lattice to the permitti vity and the quadratic and cubic susceptibilities, as well as the absorptio n of the material from the spectra of the extraordinarily polarized polarit ons. (C) 2000 MAIK "Nauka/Interperiodica".