Nonvolatile holograms are recorded in photorefractive LiTaO3:Fe with laser pulses by use of two-step excitation. Ultraviolet laser pulses (wavelength λ=355 nm) yield a strong increase of absorption (as much as 600 m-1 at λ=633 nm) and sensitize the crystals for subsequent infrared (λ=1064 nm) holographic recording. Refractive-index changes of as much as 1.6×10-4 are achieved for intensities of the infrared light of 1011 W/m2. The saturation values are proportional to the concentration of Fe3+ ions. Nondestructive readout with infrared light is possible, and the holograms remain erasable for ultraviolet light. Typical time constants of recording and erasure are 0.5 µs for intensities of the ultraviolet light of 1011 W/m2. The results can be explained with a two-level charge-transport model.
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Imbrock et al. (1999) studied this question.
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