Acoustic hologram formation with a frequency shifted reference beam

This paper discusses an interference technique that makes it possible to directly observe and record the usually very weak light diffracted by an acoustical surface perturbation. This is accomplished by using spatial filtering techniques in combination with a frequency shifted reference beam. It is shown that the acoustically diffracted light may be visualized even in the presence of statically scattered light of much higher intensity. An experiment is described in which this technique is used to view the surface perturbations of piezoelectric ceramic material caused by acoustic surface waves. The application of this system to acoustic holography is discussed in detail. This application makes use of the fact that bulk acoustic waves in a material, upon striking the surface at some acute angle, cause surface ripple patterns which form a dynamic hologram of the acoustic field. A photographic image of this hologram frozen in time may then be recorded using the process discussed above.