Spatial dependence of the dynamic optical transfer function of a transparent medium perturbed by an acoustic signal

Abstract

Based on a spatially dependent (SD) dynamic optical transfer function (DOTF) of a medium perturbed by an acoustic signal, a dynamic theory has been developed of the acousto-optical interaction (AOI) of light beams in the field of an arbitrary acoustic signal under conditions of the diffraction distortion of its amplitude profile (DDAP). A system of integro-differential equations is derived for angular and frequency DOTF spectra of coupled waves in the AOI region. An analytical DOTF model has been constructed for a weak acousto-optical coupling. The characteristics of transient processes (TPs) in the diffracted-beam field have been investigated for the spatially dependent DOTF. It is demonstrated that in most practical situations this dependence is manifested rather strongly; however, it does not always affect the TP. Thus, when the light and acoustic beam apertures exceed some characteristic values d* and L*, related to the acoustic frequency and speed and the AOI geometry, the effect of the SD DOTF on the transient process can be neglected. Otherwise, the DDAP leads to the asymmetry of the dynamic dependences of the field amplitude of the off-axis angular-spectrum components of the diffracted beam. The parameters d* and L* have been calculated for the AOI of several types in lithium niobate and paratellurite crystals. The TP characteristics are illustrated by plots calculated for the DDAP in the case of the AOI in paratellurite.