Spatial frequency dependence of the energy transfer in two-wave mixing experiments with BSO crystals

Energy transfer between two beams interfering in an electrooptic Bi₁₂SiO₂₀ crystal is analyzed as a function of the spatial frequency of the recorded hologram. We report high coefficients in a wide range of low spatial frequencies $\text{(Λ}{}^{-1}\text{?44 mm}{}^{-1}\text{)}$, when the drift length of the photocarriers becomes comparable to the fringe spacing. Exponential gain coefficients of Γ = 7 cm^-1 have been reached for high intensity beams ratio (β > 10⁴) and an optimized fringe displacement speed (moving grating recording). Application to coherent image amplification (×20) is shown.