Types of acousto-optic interactions between acoustic and circularly polarized optical waves:case of Pb₅Ge₃O₁₁...

In the present work, we analyze acousto-optic (AO) interactions between acoustic waves (AW) and circularly polarized optical eigenwaves in gyrotropic crystals. We find that the AO diffraction of circularly polarized eigenwaves can be divided into six different interaction types. Contrary to the AO interactions analyzed earlier for the case of linearly polarized optical eigenwaves, we distinguish three isotropic interaction types and three anisotropic ones. Moreover, unlike the isotropic AO interactions of linearly polarized eigenwaves of n_o-n_o and n_e-n_e interaction types, the effective elasto-optic coefficient (EEC) in the case of interactions between circularly polarized eigenwaves does not depend on the sign of an incident circular optical wave. The anisotropy of the EEC and AO figure of merit is analyzed for a particular case of lead germanate crystals, Pb₅Ge₃O₁₁. We demonstrate that the maximal AO figures of merit are achieved for type I isotropic diffraction at the quasi-longitudinal AW. Our calculations are confirmed by the experimental data obtained for the EEC using the Dixon-Cohen method. The experiment is concerned with the AO interactions of circular eigenwaves in Pb₅Ge₃O₁₁.