Effect of deviation from purely transverse and longitudinal polarization states of acoustic waves on the anisotropy of acousto-optic figure of merit: the case of Tl3AsS4 crystals.

Abstract

We analyze the effect of acoustic wave (AW) polarization states deviation from purely longitudinal and transverse on the anisotropy of the acousto-optic (AO) figure of merit for the case of AO interactions occurring in the principal crystallographic planes. In particular, we obtain phenomenological relations that describe the effective elasto-optic coefficient for the six types of AO interactions, which exhaust all of the possible isotropic AO diffractions. These relations are compared for the alternative cases when the deviations of polarization of the AWs from purely longitudinal and transverse ones are either taken into consideration or completely neglected. Our analysis carried out on the example of Tl3AsS4 crystals reveals that the deviation of AW polarization from its pure states influences the anisotropy of the AO figure of merit only when the AO interactions with quasi-transverse AWs are dealt with. This fact is caused by the peculiar acoustic and elasto-optic properties of Tl3AsS4. On the other hand, the situation can become different for other crystalline materials, where the angular dependences of the AO figure of merit can differ significantly in cases in which the deviation angle increases. This holds true for the AO interactions with both quasi-transverse and quasi-longitudinal AWs. Under these conditions, non-orthogonality of the AWs (or deviation from their longitudinal polarization states) affects essentially the AO characteristics. Finally, we determine the geometries of AO interactions for which the highest AO figures of merit are reached for the Tl3AsS4 crystals.