Scattering of light by polaritons in a lithium formate crystal

The polariton dispersion in a biaxial crystal of lithium formate was determined by the method of low-angle Raman scattering and photographic recording. In addition to the known lattice vibrations of lithium formate, this procedure revealed several new weak vibrations which were manifested as a perturbation of a strong polariton branch with which they interacted. Some of these vibrations were attributed to the secondorder spectrum.