Selective excitation of bulk and surface acoustic waves by rapid scanning of a laser interference fringe

We propose a new and effective method for selective excitation of surface acoustic waves (SAW) and bulk acoustic waves (BAW) with frequencies higher than 100 MHz using rapidly scanning interference fringes (SIF). The SIF is produced by intersecting two laser beams with a frequency difference. It works as a thermoelastic source for generating BAW and SAW. The propagating direction is given by φ = sin^-1(ν/ν_f), where ν is the BAW velocity and ν_f is the SIF scanning velocity. When the scanning velocity ν_f is equal to the SAW velocity, SAW is excited instead of BAW. Since ν_f is determined by the incident angle of the laser beams onto the surface of a tested object, selective excitation of directional BAW and SAW is achieved.