Numerical calculations of rotational contributions to the scattering coefficient in a piezoelectric LiTaO₃ crystal

A systematic theoretical analysis is presented of rotational contributions to light scattering in a piezoelectric crystal with small birefringence. The influence of rotational contributions on the intensity of nonelastically scattered light in a LiTaO₃ crystal - a trigonal system with 3m symmetry - is described. Rotation affects the optical signals that result from two quasi-transverse waves. Experimental confirmation of such rotational contributions employed a formalism based on looking for eigenvectors and eigenvalues of a so-called characteristic matrix, which is a function of the direction of acoustic-wave propagation and the elastic constants of the medium, in this case modified by the piezoelectric effect. All calculations were performed (for both the hypersonic and the ultrasonic acoustic ranges) for 514.5-nm light. Velocities of acoustic waves in the hypersonic region were calculated under elastic constants taken from 20.9 to 38.5 GHz. Hypersonic data appear more relevant for investigating the effect that consists in measuring the changes of photon frequency scattered on acoustical phonons lying at the beginning of the first Brillouin zone.