Two-frequency degeneracy of an acousto-optic interaction in paratellurite

Abstract

Earlier unknown effects of an acousto-optic interaction degeneracy in paratellurite have been studied. Its essence compared to described phenomena lies in the fact that a light beam can be diffracted twice by acoustic waves with different frequencies instead of being typically diffracted twice by the same acoustic wave. It happens due to strong acoustic anisotropy of paratellurite. Bragg conditions resulting in the degeneracy can be satisfied under a certain frequency correlation of two acoustic slow shear waves. A light beam diffracted by one spectral component of a complex acoustic signal can be effectively diffracted again by another spectral component. Thus, a physical mechanism of this effect is the same as it is in the ordinary case but it is observed under different conditions (different frequencies). Necessary calculations of such interactions have been carried out. The frequency of the ‘‘unfavorable’’ spectral component was calculated depending on the frequency of the ‘‘useful’’ one for the case of nonaxial acousto-optic interaction in paratellurite. The found effect was shown to take place and to be important for real acousto-optic devices. In the studied case, the frequencies of acoustic waves interacting with a light beam were equal to 44.7 and 43.2 MHz, respectively.