Observation of optical activity in Brillouin scattering experiments

Analytical expressions have been developed for calculating the diffraction geometry for Brillouin scattering experiments in which the applied acoustic beam and the optical wave vectors lie in a plane containing the optic axis of uniaxial crystals. A computer program solves for the diffraction angles for the general cases where the choice of crystal, crystal face, direction of acoustic propagation, plane of optical incidence, and amount of optical activity are all arbitrary. It is shown that for acoustic propagation along the X axis in quartz, the optical activity produces easily detectable changes in the angles of the incident and diffracted light beams in the XZ plane when polarization change occurs on diffraction. Moreover for this case, the optical activity produces a cutoff acoustic frequency below which Brouillin scattering with polarization rotation does not occur. Experimental measurements verify the predicted angular changes to within the accuracy permitted by the finite acoustic beam width.