Dispersion law for polaritons and temperature dependence of the refractive index of LiNbO3 in infrared range

Polariton spectra of Thomson scattering have been investigated for LiNbO3 crystal in a wide range of wave vectors at temperatures of 80, 255, 350 and 430 deg C. The dispersion dependence of the refraction factor n0 of an ordinary wave has been calculated on the basis of experimental data for visible and near infrared ranges of spectrum. N0 has been found to increase with temperature. The law of dispersion of upper branch polaritons has been constructed. The experimental law of dispersion has been compared with theoretical dependences for two models of crystal lattice vibrations