ABSTRACT
Scanned laser interferometry may be used to generate images of objects insonified in a water tank. This chapter considers the applications of laser interferometry of various types to ultrasonic measurements and visualization methods which do not also involve the use of laser-generated ultrasound. For experiments in a water tank, a reflecting surface that follows the ultrasonic displacement may be conveniently provided by the immersion of a plastic membrane or pellicle preferably having a thin aluminium or gold coating to give a good light return. To resolve the smaller amplitudes normally associated with ultrasonic frequencies, the technique of heterodyne holographic interferometry has been devised. A key feature of laser techniques for the measurement of ultrasonic surface displacement is that no contact is required and thus a change in measurement position on the surface may be made very quickly simply by the movement of a light beam.
