Peculiarities of Raman Scattering by Polaritons and Polar Optical Phonons in Anisotropic Crystals

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Abstract
The theory of the gain factor of the stimulated Raman scattering by polaritons in biaxial crystals is carried out in the fixed stationary pump field approximation. By sufficient length of the polariton wave vector the polariton scattering turns into the scattering by polar optical phonons which may be regarded as quasilongitudinal electromagnetic field quanta. Typical features of scattering by anisotropic polar phonons whose energy depends on the wave vector direction are investigated. Mixing of different symmetry mechanicalvibrations is analysed in anisotropic crystals. The Fermi resonance of polar mechanical phonons is studied in detail. Numerical calculations made for some particular cases agree with available experimental data.