PHOTOREFRACTIVE FIXING AND RELATED THERMAL EFFECTS IN LINBO3

The thermal and optical stability of photorefractive holograms written in irondoped 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 +/- 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.