EXCITATION OF HIGHER HARMONICS IN TRANSIENT LASER GRATINGS BY AN ABLATIVE MECHANISM

Laser-induced transient gratings were excited at the surface of an alu minum film by picosecond laser pulses. The counterpropagating sur;face acoustic waves with a fundamental frequency of 70 MHz that were launc hed were monitored outside the source region by laser probe beam defle ction. The second and third harmonics were observed for ablative inter action of the laser radiation with the aluminum surface. A simple mode l is presented that describes the effects on the basis of nonlinear ph otoacoustic signal generation at the source due to a nonsinusoidal dri ving force. (C) 1998 American Institute of Physics.