May the recording light change an effective trap density in photorefractive crystal?

Summary form only given. According to the existing models of photorefractive nonlinearity in the crystals lacking the symmetry center an important limitation for ultimate space charge field that can develop under the influence of light is related to the finite density of empty traps (or filled donors) characterized by an effective trap density. Within the one-center band-transport model the effective trap density is given by N/sub eff/=N/sub D//sup +/N/sub D//(N/sub D//sup +/+N/sub D/), where N/sub D//sup +/ and N/sub D/ stand for total density of donor centres and density of ionized donor centres, respectively. We show, for the first time to our knowledge, that the recording light itself gives rise to redistribution of population density of different centres and affects N/sub eff/. This effect brings the explanation to the unusual intensity dependence of photorefractive beam coupling in Sn/sub 2/P/sub 2/S/sub 6/ in the near infrared.