Optical Detection of Nanosecond Acoustic Pulses

Various optical techniques are analyzed regarding their use for narrow acoustic pulse detection. Two-beam interferometers can be used to detect surface displacements or velocities associated with surface acoustic waves. Surface gradients can be detected by the probebeam deflection technique; this method is applicable to both surface and bulk acoustic wave analysis. It is demonstrated that with a similar optical set-up focusing or defocusing (lensing effect) can be observed, which results in comparable detection sensitivity. For all the techniques described, a detection sensitivity of 10-4Á / √Hzfor surface displacement can typically be achieved. The highest frequency surface acoustic wave detectable is limited by the focal spot size to the gigahertz range. © 1986 IEEE