Optical generation of tunable ultrasonic waves

Abstract
A convenient method of optically exciting and monitoring coherent acoustic waves in transparent or light‐absorbing liquids and solids is described. The acoustic frequency is easily and continuously tunable from ≊3 MHz to at least 30 GHz with our experimental apparatus and in principle over a considerably wider range. In anisotropic materials any propagation direction can be selected. The optically generated acoustic waves can be optically amplified, cancelled, or phase shifted.