Generation of 100-mhz-band rayleigh waves by phase velocity scanning of a laser interference fringe

We investigated the thermoelastic generation of Rayleigh waves in the 100 MHz frequency range using a scanning interference fringe (SIF) obtained by intersecting two laser beams with different frequencies. A long-pulse (140 ns) Q-switched Nd: YAG laser was used to generate Rayleigh waves on an aluminum specimen at various scanning velocities controlled by the intersection angle of the laser beams. It was found that the amplitude of the generated tone burst of Rayleigh waves followed a sine function dependence over the scanning velocity with a peak at the Rayleigh wave velocity. The center frequency of the tone burst followed a linear dependence. Implications of these findings in the quantitative nondestructive evaluation of microdevice components are discussed.