1 June 1978 Long-Duration Acousto-Optic Memory Correlator
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Optical Engineering, 17(3), 173280 (1978). doi:10.1117/12.7972229
A new photorefractive effect, resulting from the interaction of high-intensity, short-duration laser pulses with propagating acoustic waves, has been found in LiNbO3. The acoustic wave pattern is stored as changes in the index of refraction (on). The On is proportional to the rf amplitude, and increases sublinearly with the number of laser pulses and as the 1.3 power of the incident laser energy density. The decay time varies from a few hours, when only green illumination (530 nm) is used, to several weeks when combined green and infrared illumination (1060 nm) are used. The On can be erased by exposure to ultraviolet radiation or by annealing at 250 C. This acousto-photorefractive effect has been utilized to construct an acousto-optic memory correlator wherein both the stored On and the On produced by a "live" propagating acoustic wave simultaneously modulate a low-power cw laser beam. The resultant detected signal is pro-portional to the correlation integral. The memory correlator operated at a center frequency of 10 MHz with a 1 MHz band-width. A large variety of complex signals, such as chirps and Barker codes, was stored and subsequently correlated. The stored signal strength is about 30 dB below that of the original live signal. Successful correlation with a live signal was achieved several weeks after storage.
N. J. Berg, B. J. Udelson, J. N. Lee, "Long-Duration Acousto-Optic Memory Correlator," Optical Engineering 17(3), 173280 (1 June 1978). https://doi.org/10.1117/12.7972229

Optical correlators



Signal detection

Wave propagation

Infrared radiation

Laser energy


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