Nonvolatile two-color holographic recording in Tb-doped LiNbO₃

We have found that Tb-doped near-stoichiometric LiNbO₃ crystals have three different types of energy levels: ultraviolet (UV) absorption centers just above the valence band, shallow electron traps slightly below the conduction band, and deep traps located about 1.9eV (λ ≈ 650 nm) below it. Using this shallow trap as an intermediate energy state, two-color holographic recording has been carried out at λ = 852 nm with a UV gating light at 313 nm. A few % of diffraction efficiency was achieved, and the measured two-color sensitivity was 0.01-0.02 cm/J. No reduction of diffraction efficiency was observed during 4 h continuous readout, and the bitor-rate of constructed digital hologram was less than 10^-5.