Probing of acoustic surface perturbations by coherent light

The need for sensitive methods of detection and visualization of acoustic surface perturbations has grown with the increasing interest in such fields as acoustic holography, ultrasonic surface wave devices, and acoustic trapped energy resonators. One very sensitive detection method utilizes a coherent light beam as a probe for locally measuring phase and amplitude of the acoustic field. Several variants of this technique are possible, based on measuring phase, deflection, wave front curvature, and spatial frequency content of the reflected beam. Each one of these variants may be combined with a scanning motion of the beam in order to visualize the entire sound field. This paper will attempt to survey the present state of the art and compare the different techniques on the basis of their sensitivity and applicability to specific requirements.