Anisotropy of the acousto-optic figure of merit for LiNbO₃ crystals: isotropic diffraction.

We have developed an approach for analyzing the anisotropy of the acousto-optic figure of merit (AOFM) for lithium niobate crystals in the case of isotropic acousto-optic (AO) diffraction. The working relations for the effective elasto-optic coefficients and the AOFM have been derived. We have found that, under the conditions of isotropic AO diffraction, the maximum AOFM value for LiNbO3 is equal to 11.62×10(-15)  s(3)/kg. This is peculiar for the geometry of AO interaction of the shear acoustic wave propagating in the Y-Z plane (the velocity 3994 m/s) with the optical wave polarized in the same plane. We have demonstrated that the maximum AOFM values are achieved mainly due to the essential anisotropy and high values of the elasto-optic coefficient of LiNbO3.