Abstract

Photorefractive gratings are most often produced by illumination of a nonlinear crystal with laser light below the band gap, and the absorbed photons induce photoexcitation and redistribution of carriers within mid-gap trap centers.¹ The photorefractive response time is longer or equal to the time needed to photoexcite a large enough number of carriers to create the space-charge field.² To increase the speed of response, beside using higher light intensities, a large absorption constant α of tire crystal may also be helpful. By doping, α can be increased only in a limited range. In contrast, large absorption constants ate observed without doping at the band edge of airy photorefractive material. Γη this region, the absorbed photons can induce Unterband phototransitions of electrons.

© 1993 Optical Society of America