Nonvolatile two-color holographic recording in Tm-doped near-stoichiometric LiNbO3

We have observed ultraviolet-induced visible absorption and performed two-color holographic recording at green, red, and near-infrared light in thulium doped near-stoichiometric LiNbO3 crystal. The diffraction efficiency and sensitivity of the recording process at all wavelengths are increased by ultraviolet gating light. Characteristics of recording in the visible are explained by a two-center model. Two-color recording in the near-infrared exhibits significant improvements of the fixed diffraction efficiency and the role of small polarons is discussed in the visible and near-infrared recording with ultraviolet sensitizing light.