Holographic memory using photochromic LiNbO₃:Tb,Fe crystals

Summary form only given. Near-stoichiometric LiNbO₃ crystals have been grown by the top-seeded solution method using the melt containing 59 mol% Li₂O and 41 mol% Nb₂O₅ with 200 ppm Tb₄O₇ and 100 ppm Fe₂O₃. A sample (a×b×c=8×3.1×10 mm³) investigated here was cut from the boule, oriented, and optically polished. The absorption spectrum of as-grown crystal was similar to that of ordinary Fe-doped crystal. However, this doubly-doped crystal exhibited a strong and thermally stable induced absorption band in the visible range when exposed to ultraviolet (UV) light. The UV-induced absorption band was very stable against thermal decay at room temperature, but could be optically bleached with visible lights. The response to UV light was very fast, and the induced absorption was saturated in a few sec. at each UV intensity. The fast coloration upon UV exposure can be effectively used for a quick erasure of the stored information if holograms are recorded from the colored state. Holographic storage was carried out using the conventional two-wave mixing technique