OPTICAL IMAGING OF SOUND FIELDS BY HETERODYNING

摘要

Bragg imaging at relatively low acoustic imaging frequencies is accomplished by Bragg diffracting light-beam lightbeam in such a way that the diffracted light from the Bragg light-sound interaction region includes an image sideband of one order or frequency and a relatively uniform field of reference light of another order or frequency which is superimposed on the image sideband at the image plane of the sideband image. The image sideband light heterodynes with the reference light to replicate the sideband image as a signal whose frequency is the beat frequency of the sideband and reference lights. The replicate heterodyne image is detected with a photodetector tuned to the beat frequency and electrically converted to an image display.