Angle-multiplexed hologram storage in LiNbO₃:Tb, Fe

We have performed hologram multiplexing with a cw laser at λ = 532 nm in a near-stoichiometric LiNbO₃ :Tb, Fe crystal that exhibits a visible absorption band induced by UV light. When 50 plane-wave holograms were angle multiplexed from the UV preexposed state, the recording sensitivity gradually decreased, owing to bleaching of the induced absorption. However, a conventional recording schedule of multiplexing many holograms of equal diffraction efficiency can be used in this photochromic material. The gradual decrease in recording sensitivity throughout multiplexing can be compensated for by the increased erasure-time constants of later-written holograms. An M/# of 1.73 was obtained in a crystal of 3.3-mm thickness.