I. C. Khoo, Department of Electrical Engineering, Pennsylvania State University, University Park, Pa.
Interest in materials that exhibit photorefractivity has been very intense, due to their capabilities for low power optical wave mixing applications, which include phase conjugation, image and signal processing, and holographic storage. Currently, inorganic photorefractive crystals are the materials of choice. These crystals are quite expensive and hard to grow. Moreover, the spectral response of these materials is limited to the visible-1 μm range. There has also been recent work on polymer-based photorefractive materials; they, however, require very high dc fields (several tens of kilovolts/ centimeter), respond slowly, and are applicable over a limited spectral region just as inorganic crystals.
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