Abstract

When a Bi₁₂SiO₂₀ crystal is used for two-wave photorefractive amplification and a constant voltage is applied to the crystal, the gain may be considerably enhanced by detuning one of the incident beams to produce a moving grating. Simple theory shows that the gain versus detuning curve has a single maximum that depends on the total incident intensity. When crystals with lengths greater than a few millimeters are used, one must take into account the effects of optical activity and absorption, the anisotropic nature of the photorefractive effect in Bi₁₂SiO₂₀ causes alternating regions of high and low coupling constants as the plane of polarization of the two beams rotates through the crystal under the influence of optical activity. In the particular example where the crystal length is such that there are two regions of high coupling constant at the beginning and the end of the crystal, the average intensities within the two regions will be different because of absorption, and the optimum detuning frequencies for the two regions will also be different. This results in a double maximum in the detuning curve. Theoretical predictions of multiple peaks have been experimentally confirmed.

© 1990 Optical Society of America