Real-Time Display of Sound Holograms by KD*P Modulation of a Coherent Light Source

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Abstract
It is possible to reconstruct optically a sound hologram by reflecting a laser beam from the pattern formed on the water surface [R. K. Mueller and N. K. Sheridon, Appl. Phys. Letters 3, 328 (1966)]. The acoustically illuminated object is then viewed in real time but the quality of the reconstruction is poor because of aberrations due to streaming and oscillatory surface disturbances. A way of improving the real time reconstruction process is presented, in which the holographic pattern is recorded on the surface of a piezoelectric crystal (quartz), immersed in the water, and then forms the end wall of a Sokolof-type electron tube. A scanning electron beam reads off the corresponding voltage pattern obtained on the surface of the piezoelectric crystal. It produces an output signal that is then applied to a deuterated KDP crystal (KD*P) scanned by an electron beam synchronized with that of the first tube. It is therefore possible to modulate the index of refraction of KD*P (Pockels effect) and obtain phase modulation corresponding point by point to the holographic pattern recorded on the quartz surface. Illumination (reflection or transmission) of the crystal with laser light will permit optical reconstruction of acoustically illuminated objects. This device permits a scale change of the hologram that reduces aberrations.
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