Photoacoustic generation and detection of 10-ns acoustic pulses in solids

We describe the generation and detection of short acoustic pulses (∼10-ns widths) in opaque plates, using weak laser pulses (less than 1-mJ energy) for excitation. The longitudinal, shear, and surface acoustic waves generated by a single laser pulse can be time resolved by using a thin-film piezoelectric transducer, and acoustic mode conversions at surfaces are clearly observable. This new photoacoustic material testing technique is useful for fast ultrasonic measurements or for detecting deep subsurface flaws.