Probing acoustic nonlinearity on lengths scales comparable to material grain dimensions.

The focus of this presentation is to describe our efforts at laser generation of high frequency surface acoustic waves and detection of the nonlinear contribution in the acoustic near-field of the source. Narrow band acoustic generation is accomplished by interfering two pulsed laser beams at the surface of the sample. A Michelson interferometer, that incorporates a high power microscope objective, is used to detect the acoustic disturbance. Detection near the source combined with high frequency generation (approximately 0.1 GHz) facilitates investigation of fundamental processes of harmonic generation on length scales comparable to grain size dimensions.