THEORY OF 2-CENTER TRANSPORT IN PHOTOREFRACTIVE MEDIA FOR LOW-INTENSITY, CONTINUOUS-WAVE ILLUMINATION IN THE QUASI-STEADY-STATE LIMIT

A two-center photorefractive model permitting all center-to-band trans itions and electron-hole charge transport unifies several models descr ibing subsets of these transitions. Using the quasi-steady-state appro ximation for low continuous-wave illumination, the model derives the f irst-order Fourier harmonic of the steady-state space-charge distribut ion and fields and the corresponding response rates. The model describ es electron-hole competition, complementary gratings, double-exponenti al time-dependent behavior, and non-linear dependence of response rate s on intensity. The model can be used to make new predictions of photo refractive behavior of crystals in which two species of impurity cente r are present; an example is presented for BaTiO3.