Abstract

Surface acoustic waves (SAWs) provide a powerful tool to probe the surface region of materials. The advent of short laser pulses has allowed the excitation of broadband SAWs on nonpiezoelectric substrates. Since SAWs penetrate only one or two wavelengths into the substrate, different depths can be probed simultaneously by pulsed experiments. In addition, modification of the surface morphology, surface contamination or thin films on the substrate surface may be detected by changes in the acoustic phase velocity or the acoustic pulse shape. In our experiments, the SAW pulses were excited with a 10-ps pulse at a wavelength of 248 nm. The bandwidth of the excited pulse was limited to 200 Hz by the width of the line focus on the surface. The SAW pulses were detected at a distance of several centimeters from the excitation by a 6-µm thick ferroelectric foil of a copolymer of polyvinylidenefluoride and trifluoroethylene pressed onto the sample with a tungsten wedge with a 1-µm diameter radius.

© 1991 Optical Society of America