High photorefractive gain in two-beam coupling with moving fringes in GaAs:Cr crystals

We report two-beam coupling experiments at 1.06-microm wavelength using photorefractive semi-insulating GaAs:Cr in the moving-grating recording mode. The steady-state gain coefficient r is measured as a function of fringe spacing Lambda, fringe velocity v, applied voltage V0, and incident beam ratio beta. A maximum Gamma as high as 6-7 cm(-1) is observed for Lambda approximately 18 microm, v approximately 1 mm/sec, beta > 10(3), and V(0) approximately 5 kV (interelectrode distance 5.8 mm). The agreement with the theory of two-beam coupling with moving fringes is discussed. In particular, a set of numerical values is obtained for some crystal parameters. Image amplification is demonstrated.