Long-term readout of photorefractive memories by using a storage/amplification two-crystal configuration

We propose and demonstrate a new long-term readout holographic memory using two photorefractive crystals. Images are stored in the first crystal and reconstructed with low-intensity beams, then amplified in the second crystal operating in a high-gain low-noise configuration. By using combinations of LiNbO(3)/Bi(12)SiO(20) and BaTiO(3)/Bi(12)SiO(20) as storage/amplification crystals, continuous readout of the angularly coded memories for more than 20 h and 40 min, respectively, is experimentally achieved. A lower bound for the index modulation to be allocated to one stored image in LiNbO(3)is estimated.