Peculiarities of the acousto-optical field formed during diffraction of dual-mode radiation in uniaxial crystals

Abstract

This paper discusses acousto-optic Bragg diffraction in uniaxial crystals when two intrinsic optical modes of the crystal participate in the diffraction. The calculations are based on two crystals widely used in acousto-optics: lithium niobate and paratellurite. It is shown that the character of the acousto-optical field formed in the diffraction orders when optical rays propagate close to the optic axis while a sound wave propagates orthogonally to the optic axis makes it possible to use the resulting field for two-dimensional processing of optical images. The image can be filtered in this case by using both the zeroth and the first diffraction orders. Acousto-optic filters are fabricated from a paratellurite crystal and are used to experimentally show that a two-dimensional contour is discriminated when the image is subjected to optical Fourier processing (fast Fourier transform), using the zeroth and first Bragg orders.