24 August 2006 High-frequency photorefractive amplification for ATR applications
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Abstract
Automatic target recognition (ATR) can be accomplished by many methods, including recognition of vibrometric signatures. In many cases, ATR is enhanced by photorefractive amplification, a two-wave mixing effect in which two input beams form a dynamic holographic grating. One of the two beams (the pump) diffracts from that grating into the other (the signal), assuming the characteristics of the signal. When the pump is much stronger than the signal, the diffracted pump becomes a highly amplified signal beam. Traditionally, however, the frequency at which this amplification can be applied is limited to <1/2πτ0, where τ0 is the decay time of the grating in the absence of a pump or signal. We demonstrate that the amplification has no such limit in the case of vibrometry, which measures frequency-modulated, rather than amplitude-modulated, signals. This is shown by constant photorefractive amplification at frequencies up to >700 kHz in Cu:KNSBN, which has τ0 >100 ms (corresponding to a maximum amplification frequency of 1.6 Hz).
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Russell M. Kurtz, Albert O. Okorogu, Judy Piranian, Gilda Fathi, Kang-Bin Chua, Ranjit D. Pradhan, Thomas C. Forrester, Tomasz P. Jannson, "High-frequency photorefractive amplification for ATR applications", Proc. SPIE 6314, Photorefractive Fiber and Crystal Devices: Materials, Optical Properties, and Applications XII, 63140O (24 August 2006); doi: 10.1117/12.679763; https://doi.org/10.1117/12.679763
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KEYWORDS
Crystals

Automatic target recognition

Modulators

Laser crystals

Copper

Photorefraction

Phase modulation

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