Collinear Anisotropic Light Diffraction by Standing Elastic Waves Along X-Axis of Lithium Niobate Crystal

The authors of some works devoted to the collinear light diffraction by standing elastic wave base their researching on the theory of acoustooptic interaction on a moving ultrasonic wave (e.g., see [1]). According to qualitative methods it is clear the effect of collinear anisotropic light diffraction by a standing acoustic wave has to lead to the amplitude modulation of light. Unfortunately, there is no theory for collinear anisotropic light diffraction by standing waves today. The attempt to describe the noncollinear quasi-isotropic Bragg diffraction by standing elastic waves was presented in the paper [2], where it is noted the amplitude light modulation as a result. In present work the collinear anisotropic diffraction of light by the standing longitudinal elastic wave composed of two contradirectional waves along x-axis of lithium niobate crystal is presented. At the beginning the mentioned problem is discussed using the diagrams of wave vectors. It is importantly to note there are two situations of collinear anisotropic diffractions: with summation and with subtraction between phase vectors or frequencies of optic and acoustic waves, so diffracted light depends on choice of diffraction-s way. There are three optic waves of one polarization and two waves of other one as a result of the acoustooptic interaction. The first optic group is represented by passed beam and two satellites of diffracted light with frequencies remote on double value of acoustic frequency from incident optic one. Basing on electromagnetic wave equation the system of different ones for the acoustooptic interaction in five-waves approximation is obtained. By numerical computing the mentioned system is analyzed applying the method of successive approximations. The distributions of diffracted and passed field-s strengths depending on an interaction-s length and acoustic frequency are shown in graphic pictures. Basing on the suggested theory of a collinear anisotropic light diffraction by standing acoustic wave it is possible to choose the necessary acousto-optic interaction-s length and ultrasonic frequency for experimental models of the acousto-optic modulator with required performances.