Measurement of surface acoustic wave slowness curves with a scanning laser acoustic microscope

The measurement of the velocity and power flow angle of surface acoustic waves (SAWs) using a scanning laser acoustic microscope is described. Data obtained from a single scan by the microscope and from a single direction of insonification are Fourier transformed from the spatial domain into the spatial frequency domain. The incident cw surface waves scatter from the sides of the sample into all possible wave vectors. Thus, the Fourier transform in the spatial frequency domain is the inverse velocity or slowness curve for surface waves propagating on the material. From this curve, the phase velocity, group velocity, and power flow angle versus propagation direction can be obtained. Experimental results for YZ lithium niobate, ST quartz, and (111) silicon are in good agreement with theoretical calculations.