Laser-induced surface acoustic waves and photothermal surface gratings generated by crossing two pulsed laser beams

Gigahertz surface acoustic waves have been optically generated and detected on aluminum metallic films and silicon wafers using the laser-induced grating technique. The acoustic velocities were in good agreement with those of Rayleigh waves. Photothermal surface gratings could also be detected as a nonpropagating component of the thermoelastic waves. The relaxation time of the grating was related to the thermal diffusivity of the material. A simplified theory for the generation of surface transient gratings containing acoustic waves is presented in addition to the experimental results.