An optical heterodyne ultrasonic image converter

The theory and preliminary experimental results for a new type of ultrasonic image converter system are presented. The method uses a scanning laser transmitter and receiver, operating as an optical heterodyne system, to sense the vibration amplitude distribution on a reflective resonant diaphragm placed in the liquid acoustic medium. The output of the optical heterodyne receiver is displayed as an optical image on a cathode ray tube. If an acoustic image is formed on the diaphragm, either by means of acoustic lenses or by shadow imaging, the corresponding pattern will be present in the visible display. Sensitivity to low sound levels is comparable to the best alternate methods for much of the frequency spectrum of interest in this work. Acoustic holograms also can be recorded by this technique, which should be practical with very large acoustic apertures.