Two-color holography in Tb-doped near-stoichiometric LiNbO/sub 3/

Summary form only given.We have found that Tb-doped nearstoichiometric LiNbO/sub 3/ has three different types of energy levels: UV absorption centers just above the valence band, metastable shallow electron traps slightly below the conduction band, and deep traps about 1.9 eV below the conduction band. Irradiation with UV light induced a new stable absorption band extending from 650 nm to the absorption edge. The temporal evolution of induced absorption revealed that the crystals have shallow electron traps and deep traps located about at least 1.9 eV below it, and that the deep-trapped charges give rise to this UV-induced visible absorption band. The electron lifetime at shallow traps was about 4 s, and the deep-trap dark decay time was estimated to be over two years. Using shallow traps as intermediate energy levels, two-color nonvolatile holographic recording has been carried out by use of CW recording beams at /spl lambda/=852 nm and incoherent UV gating light. Diffraction efficiency of several % was achieved, and the measured sensitivity was 0.01-0.02 cm/J, comparable to those reported for bipolaron-based two-color holography. The stored hologram suffers a substantial dark decay at the initial stage of readout process. This is because the shallow trap lifetime, 4 s, is rather long. This initial decaying component could be reduced by employing excess recording in which the gating beam is shut off a certain time before the recording is finished.