Application of laser-based linear and nonlinear surface acoustic waves in materials analysis

Pulsed ns or ps Nd:YAG lasers were used to excite surface acoustic wave pul ses and gratings. Michelson interferometry and laser probe-beam deflection were employed to monitor the transient surface displacement and surface vel ocity, respectively. The thickness and elastic constants of amorphous layer s generated by ion implantation in a silicon crystal wafer were determined. The propagation of broadband nonlinear surface pulses in anisotropic silic on crystals was studied experimentally and theoretically. The excitation of narrowband nonlinear transient gratings on a silicon surface was achieved. In this case generation of higher harmonics was caused by the nonlinear ph otoacoustic excitation process at the source and not by propagation in a no nlinear medium.