Photorefractive fixing and related thermal effects in LiNbO3

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Abstract
The thermal and optical stability of photorefractive holograms written in iron-doped LiNbO3 have been measured over the temperature range from 50 to 165 degrees C. In each case the decay proceeded as a non-simple exponential process exhibiting several more or less resolvable stages. For optically erased holograms the activation energy of the two observed stages was 0.15+or-0.01 eV. Thermal erasure revealed at least four stages with activation energies ranging from 0.85 to 0.95 eV. Homogeneous illumination at room temperature gave rise to a fixed-developed hologram whose diffracted signal was about 1% of that shown by the initially light-recorded hologram. The developed signal was approximately the same after four successive erasing-developing cycles. Thermal erasure results are interpreted in terms of only proton migration, within the framework of recent models for photorefractive fixing. Thermal electron detrapping proceeds at higher temperatures (t>170 degrees C) in lightly reduced samples.