Visualization of ultrasonic wave fronts using holographic interferometry.

Holographic interferometry with a phase-modulated reference beam is used to visualize a progressive ultrasonic wave in the interior of a transparent medium. The medium is illuminated with sheetlike light, and the light scattered from the plane of the light sheet is recorded in the hologram. The ultrasonic field on the plane is obtained from the reconstructed image, which provides the equiphase positions of the wave, i.e., wave fronts. Experiments were performed at 200-kHz frequency. The effect of flow in the medium is estimated. An analysis of the optical system suggests that this method is applicable to ultrasonic waves with frequencies up to ~6 MHz.