Time-Intergrating Self-Pumped Phase Conjugator,
CENTER FOR APPLIED OPTICS STUDIES TERRA HAUTE IN
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Huignard presented a speckle-free imaging processor using a BSO crystal and four-wave mixing. The input beam passed through a diffuser screen which was a mounted on step by step rotation motor. Four-wave mixing generated a phase-conjugated beam which was time-integrated with a Polaroid camera. Ford and coworkers investigated the effect of a photorefractive PR fanout on a time-varying input. When a time-varying input was imaged into the PR gain medium the time-independent portion of the input signal fanned out while the time-varying portion transmitted. Thus, the PR gain medium acted as a novelty filter, transmitting the changes in the input immediately and fanning out the portion which was stationary for a time longer than the PR gain medium response time pi. In this paper a time-integrating filter using self-pumped phase conjugation SPPC is described. When a time-varying input is sent into the PR crystal, SPPC will occur for the constant portions of the input. The PR crystal acts as a novelty filter, causing SPPC for the stationary input and transmitting the changes in the input which are varying in time shorter than pi, the PR crystal response time. The time variation of the speckle pattern is governed by the characteristic time constant T. The characteristic time T of a moving specklegram in defined as the time for which an average speckle grain needs to displace itself.