Cameras for acoustic holography

Claim 1

An acoustic holography camera for displaying the acoustic hologram of an object from which an ultrasonic wave of frequency Fo emerges, said camera comprising: an acoustic plate set into vibration by said ultrasonic wave; a photodetector; a monchromatic radiation source emitting a primary parallel beam; an interferometric device including beam splitter means to split said primary beam into a secondary object beam and a secondary reference beam, and projecting means to project a fraction of said secondary beams onto said photodetector, said object beam experiencing reflexion on said acoustic plate before reaching said projecting means; scanning means to produce displacements of said object beam at the surface of said plate; display means; transducer means to provide to said display means voltages indicative of the amplitude of said displacements of said object beam; electrical transmission means including filter means and squarelaw detection means and being cascade arranged between said photodetector and said display means; said interferometric device further including modulating means and frequency shift means, both arranged on the path of one of said secondary beams, said modulating means modulating the optical length of said one secondary beam at said frequency Fo and frequency shift means shifting the frequency of said one secondary beam by a predetermined amount F1, said frequency F1 being in execess of Fo.