Inverse Raman Effect by Polaritons in LiIO 3 Single Crystals

First experimental observation of inverse Raman scattering (IRS) from polaritons are reported. The IRS frequency shifts measured in LiIO 3 crystals using different scattering geometries are discussed and compared with SRS experiments. Using extraordinary continua and ordinary laser fields, the polaritons associated with the 769 cm −1 El‐phonon shift to 595 cm −1 . In addition in this scattering geometry an absorption at 860 cm‐I was detected, due to a polariton in the upper dispersion branch. It is shown that the polariton absorption frequencies in IRS can be determined as in SRS from “undamped” quasi ‐momentum conservation laws. The IRS absorption coefficient for polaritons has a Lorentzian form. In some scattering geometries in anisotropic crystals, IRS and SRS can result in different polariton frequencies for the same fixed laser polarization; especially large polariton shifts in SRS are accompanied by small shifts in IRS and vice versa.