Optical monitoring of photoacoustic pulse propagation in silicon wafers

We demonstrate a new optical and noncontact method for direct and fast detection of photoacoustic pulse propagation in thin silicon wafers. A probe beam deflection technique is used to monitor both longitudinal and Lamb wave propagations from which information on the elastic constants and the sample orientation can be obtained. Results obtained for wafers of different orientations and doping levels are compared with previous contact measurements.