Acoustooptical diognostics of ultrasonic Lamb waves by the Bessel light beams in gyrotropic sillenite type crystels

It is shown that, for Bessel light beam, it is possible to separately observe isotropic and anisotropic Bragg diffraction of circularly polarized waves on Lamb modes in gyrotropic cubic crystals. In this case, the effective acousto-optical interaction in the transmitted and reflected diffraction orders is realized in a narrow range of layer thickness near the mode cut-off thickness. Of greatest for acousto-optic diagnostics of Lamb modes is the zero mode of a Bessel light beam under the condition of isotropic diffraction of circularly polarized waves with accurate transverse phase synchronism of the diffracted beams.