Optical generation and detection of surface acoustic waves on a sphere

Abstract

Surface acoustic waves (SAW’s) have been optically generated and detected on metallic spheres. The source was a focused yttrium aluminum garnet (YAG) laser operated in the Q-switched mode and the probe was a sensitive optical heterodyne interferometer. The curvature of the surface gives rise to dispersive effects. The variation of the SAW group velocity is deduced from the evolving waveforms of pulses detected after propagating a few turns around the sphere. The observation of SAW pulse waveforms at positions away from the pole (a point diametrically opposite to the source) reveals that the spectral components undergo a π-phase shift when passing through the pole.