Possibility for photorefractive effects in organic electrooptic crystals

Abstract

The mechanism of photorefraction is described, and the crystal properties that contribute to photorefractive performance are identified. They are the linear electrooptical effects; the number and type of charge carrier traps, which allow rearrangement of the space charge; and the photoconductivity property, which increases with increasing trap photoionization rates, carrier mobilities, and carrier lifetimes. In inorganic photorefractive materials the ratio of the electrooptic coefficient to the dielectric constant does not vary by more than an order of magnitude, so to achieve higher diffraction efficiency, one must usually be content with a slower speed of response. Organic crystals do not suffer from this limitation. Problems to be overcome in the search for suitable organic photorefractive materials are outlined.