Abstract

The dark decay time of volume phase holograms recorded in photorefractive potassium niobate crystals mainly depends on the dark conductivity of the material. Self-erasure time constants between some microseconds and a few seconds are observed in general in KNbO₃. We report dynamical effects during the build-up and the dark decay of photorefractive gratings recorded in nominally pure KNbO₃ samples at temperatures higher than 70°C. Under these conditions bipolar charge transport takes place.¹ The thermal activation energies of electrons and holes are different and we demonstrate that the storage and fixing of phase holograms is possible by simoultaneous optical recording and thermal treatment. We can increase in this way the storage time of the hologram by more than a factor 10⁵.

© 1990 Optical Society of America