Abstract
Two-step excitation processes have been used for hologram storage in photorefractive crystals. Then the interference pattern can be formed with red or near-IR light and nondestructive readout of information is possible. Often shallow levels are involved in the holographic recording process in photorefractive crystals. The shallow levels can be populated by illumination with visible or UV pulses forming states with relatively long life times, thus sensitizing the crystals for holographic recording with IR pulses. In LiNbO3 and LiTaO3 the most important shallow levels have been identified. They result from NbLi5+ and TaLi5+ antisite defects (Nb5+ or Ta5+ on Li+ site). The crystals can also be pre-illuminated with visible light of a cw argon laser or of a Xenon lamp and holograms can be recorded with red light of a laser diode. The sensitization process is possible for other photorefractive crystals, too. The holograms can be read nondestructively with IR light and can be erased with green light.
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Eckhard E. Kraetzig, Eckhard E. Kraetzig, } "IR recording in photorefractive crystals via two-step processes", Proc. SPIE 4459, Photorefractive Fiber and Crystal Devices: Materials, Optical Properties, and Applications VII, and Optical Data Storage, (23 January 2002); doi: 10.1117/12.454007; https://doi.org/10.1117/12.454007
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