New method for the generation of surface acoustic waves of high frequency

We describe a variation of the picosecond ultrasonic technique that can be used to generate high-frequency surface waves. A transmission diffraction grating is formed on a transparent wafer, and then placed very close to the surface of the sample. A light pulse passing through the grating will give rise to a spatially varying light intensity on the sample. This sets up a periodic thermal stress on the sample surface, which in turn generates a standing surface acoustic wave. This wave has a wavelength equal to the line spacing of the grating. The range of frequencies of waves that can be generated by this technique is limited only by the lithographic techniques available for the fabrication of the grating. In this paper, we will present a number of experimental results obtained with this new method, and will also report on measurements made with gratings deposited directly onto the samples.