Direct Observation of Acoustical Activity inαQuartz

A rotation of the polarization of microwave-frequency (1.05-1.40 GHz) shear waves propagating close to the optical axis in α quartz has been observed. This constitutes the first direct ultrasonic measurement of the phenomenon of acoustical activity predicted by Portigal and Burstein. The magnitude of the acoustical activity is in good agreement with that calculated from a recent Brillouin-scattering determination of the linear wave-vector---velocity splitting of the two transverse-acoustic normal modes. A rotary power of {~} 3-5 rad/cm is observed at these frequencies; the sense of the rotation is opposite that of the optical activity.