Saturation of absorption and rotation of polarization of radiation by local vibrations in cubic crystals

The separation of the absorption of linearly polarized resonant radiation by anharmonic local vibrations of cubic symmetry is analyzed by the method of the quantum kinetic equation. It is shown that as a result of the symmetry-induced degeneracy of the energy levels the absorption saturation is accompanied by rotation of the radiation polarization towards one of the symmetry axes of the crystal. The direction and rate of rotation are determined by the ratio of the relaxation parameters of the local vibration. An analogous rotation is investigated in the case of tunnel centers. The extreme direction of the polarization is determined in this case by orientation of the centers.