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 transitions and electron-hole charge transport unifies several models describing subsets of these transitions. Using the quasi-steady-state approximation for low continuous-wave illumination, the model derives the first-order Fourier harmonic of the steady-state space-charge distribution and fields and the corresponding response rates. The model describes electron-hole competition, complementary gratings, double-exponential time-dependent behavior, and non-linear dependence of response rates on intensity. The model can be used to make new predictions of photorefractive behavior of crystals in which two species of impurity center are present; an example is presented for BaTiO3.