Abstract

Polarization-flip photorefractive two-beam coupling is a nonlinear process in which two input beams of the same polarization can generate a beam of an orthogonal polarization. The electrooptic tensor elements in photorefractive cubic crystals such as Bi₁₂SiO₂₀ (BSO) and GaAs allow this type of coupling for certain crystal orientations. Recently, the theoretical analysis of this concept has been reported¹ for all cubic photorefractive crystals; the experimental results in GaAs have also been reported.² Here we present experimental studies of polarization-flip two-beam coupling in photorefractive BSO using Ar⁺ laser beams. The experiment consists of two right-hand polarization beams (pump and probe) intersecting in the crystal and monitoring the left-hand circular polarization component of the probe beam. Because of optical activity in BSO, circular polarizations were used as the normal propagation modes of the crystal. We have observed as much as a 50 times gain in the polarization-flipped component over the background noise, which is mostly due to leakage of a nonflipped signal through the polarizers. There is some phase mismatch between the right- and left-hand circular polarization beams, and this can cause the two beams to exit the crystal at slightly different angles. We compare our data to the theoretical prediction given in Ref. ¹. We also report the results of applying external electric field and moving the grating to possibly improve the value of γ.

© 1987 Optical Society of America