Some features of acousto-optic interaction of optical and acoustic Bessel beams in transversely isotropic optically positive crystals

Some basic properties of acousto-optical (AO) diffraction involving Bessel light and acoustic beams in anisotropic crystals are investigated. Hexagonal symmetry crystals are considered and are optically uniaxial and positive and acoustically transversely isotropic. It is shown that, unlike the case of AO diffraction of plane waves, the transition to Bessel beams allows one to realize a number of new diffraction channels having specific configurations of the wave vectors of interacting waves while maintaining the axial symmetry of the optical scheme as a whole. The diffraction channels for anisotropic scattering are classified and the main parameters of the scattered Bessel light beam and the parameters of the Bessel acoustic beam are calculated for each of them. The possibility of implementing the isotropic-type diffraction was revealed, which makes it possible to increase the efficiency of AO conversion. The parameters of this-type diffraction are determined for two scattering channels, namely, for scattering by a direct Bessel acoustic beam and by a backward propagating acoustic beam. Due to the appearance of a set of scattering channels and with regard to the fact that Bessel light and acoustic beams have helical wave front dislocations, as well as suppressed diffraction spreading, the study of the features of AO diffraction of such beams in optically positive crystals has both a scientific and practical interest.