Collinear diffraction of light on ultrasound under the conditions of strong interaction

Some equations that couple the amplitudes of transmitted and diffracted light beams interacting in an anisotropic medium with slightly divergent acoustic beam are derived. The acoustic beam is generated in the medium by means of a piezotransducer whose transverse dimensions are bigger in comparison with a sound wavelength. The acoustic beam parameters are defined by the transducer dimensions under the conditions of parabolic equations of sound propagation satisfaction. In the interaction area the incident light beam has a determined polarization and directed parallel to the acoustic beam. The anisotropic diffraction of this beam on sound is accompanied by the appearance of diffracted beam that has the same direction of propagation as the incident one, but polarized orthogonally to the direction of polarization of incident beam. If both light beams satisfy the parabolic equation of propagation, then two first-order equations can be formulated that bound Fourier spectra of transmitted and diffracted light beams and acoustic beam in their interaction region. By solving these two equations at the proper boundary conditions one can acquire the diffracted light beam longitudinal and transversal amplitude distribution. some particular cases of transversal distribution of acoustic and light beams are analyzed. It is shown that the diminishing of cross section of acoustic beam is accompanied by a bandwidth broadening of a transmission of an acousto-optic cell and by a shift of the center of this band relative to the point corresponding to the optimal interaction of the plane acoustic and light waves.