Amplified phase-conjugate beam reflection by four-wave mixing with photorefractive Bi(12)SiO(20) crystals.

Phase-conjugate beam reflectivity in photorefractive Bi(12)SiO(20) (BSO) crystals is analyzed as a function of the following parameters involved in the four-wave mixing interaction: grating spatial frequency Lambda(-1), applied field E(0), and incident beam ratio beta. We report an amplified reflectivity (R = 2.7) for asymmetric pump-beam intensities and optimized fringe-displacement speed (moving-grating recording mode, E(0) = 10 kV cm(-1); Lambda(-1) approximately 45 mm(-1); beta > 10(4)). The conjugate-beam reflectivity is shown to depend closely on the same parameters as the exponential gain coefficient Gamma of the two-wave mixing configuration. Still higher reflectivities (R' = 35) are demonstrated by using a combination of two BSO crystals whose roles are, respectively, to generate and then to amplify the conjugate beam.