Increase in the acousto-optic figure of merit in SiO2 crystals due to optical activity. Anisotropic acousto-optic interactions

We analyze anisotropic acousto-optic (AO) interactions of three possible acoustic eigenwaves with the incident and diffracted optical eigenwaves elliptically polarized due to optical activity effect in quartz crystals. Dependences of the effective elasto-optic (EO) coefficient and the AO figure of merit on the diffraction angle are obtained. We demonstrate that proper accounting for a nonzero ellipticity of the optical eigenwaves leads to nonzero values of some effective EO coefficients and a presence of the corresponding AO interactions of so-called types VII and VIII. We also reveal the effect of non-orthogonality of the acoustic waves on the effective EO coefficient and the AO figure of merit at the AO interactions of the types VII and VIII. The ellipticity of the optical eigenwaves manifests itself in peak-like angular maxima of the effective EO coefficient and the AO figure of merit for all the types of AO interactions under consideration. These maxima appear around the diffraction angles 0 and 180 deg that correspond to the collinear AO interaction between the circularly polarized optical waves propagating along the optic axis. The maximal values of the AO figure of merit in this case are respectively equal to 1.16x10-15, 0.36x10-15 and 0.48x10-15s3/kg at the types VII, VIII and IX of AO interactions. Finally, we show that a deviation of the incidence angle from 90 deg at the interaction types VII and VIII leads to zeroing of the effective EO coefficient and the AO figure of merit.