VOLUME-HOLOGRAPHIC MEMORY FOR LASER THREAT DISCRIMINATION

Using conventional volume-holographic angle multiplexing in an Fe:LihT bO(3) crystal, we have developed a compact laser threat discriminator, intended for aircraft integration, that optically detects laser spati al coherence and angle of arrival while simultaneously rejecting incoh erent background sources, such as the Sun. The device is intended for a specific type of psychophysical laser attack against U.S. Air Force pilots, namely, third-world-country exploitation of inexpensive and po werful cw Ar-ion or doubled Nd:YAG lasers in the visible spectrum to b lind or disorient U.S. pilots. The component does not solve the genera l tactical laser weapon situation, which includes identifying precisio n-guided munitions, range finders, and lidar systems that use pulsed i nfrared lasers. These are fundamentally different threats requiring di fferent detector solutions. The device incorporates a sequence of high ly redundant, simple black-and-white warning patterns that are keyed t o be reconstructed as the incident laser threat, playing the role of a n uncooperative probe beam, changes angle with respect to the crystal. The device tracks both azimuth and elevation, using a nonconventional hologram viewing system. Recording and playback conditions are simpli fied because nonzero cross talk is a desirable feature of this discrim inator, inasmuch as our application requires a nonzero probability of detection for arbitrary directions of arrival within the sensor's fiel d of view. The device can exploit phase-matched grating trade-off with probe-beam wavelength, accommodating wavelength-tunable threats, whil e still maintaining high direction-of-arrival tracking accuracy. (C) 1 996 Optical Society of America.