Optimum conditions for high-fidelity holographic storage in photorefractive crystals

We present theoretical and experimental investigations on diffraction properties of transmission-type gratings in photorefractive crystals under the conditions of strong beam coupling effect between two writing beams. By using the coupled-recording-wave approach, the diffraction efficiency is derived as a function of intensity ratio of the two writing beams, the beam coupling constant, and the phase-shift between the interference fringes. Two configurations are discussed with π/2 and -π/2 phase shift between the interference fringes and the refractive index gratings. The theoretical results suggest that the case of π/2 phase shift has the optimum conditions for high-fidelity holographic storage of the gray-level images. On the other hand, the case of -π/2 phase shift is suitable for information processing in the Fourier plane. The experimental results are in agreement with the theoretical predictions.