Nonvolatile holograms are recorded in photorefractive with laser pulses by use of two-step excitation. Ultraviolet laser pulses (wavelength ) yield a strong increase of absorption (as much as 600 m-1 at ) and sensitize the crystals for subsequent infrared holographic recording. Refractive-index changes of as much as are achieved for intensities of the infrared light of The saturation values are proportional to the concentration of 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 The results can be explained with a two-level charge-transport model.
© 1999 Optical Society of America