Dependence of the refractive index grating in photorefractive barium titanate on intensity

The interference pattern of light waves creates a refractive index modulation in photorefractive media. This process is relatively well described by the theory (Kukhtarev equations) but deviations are found. Therefore, experimental methods are used in order to characterise the processes. The influence of the absolute intensity as well as the intensity ratio of the interfering waves on the refractive index modulation are studied in a two-wave mixing arrangement. Especially for the dependence on the absolute intensity the interesting relation Δn=f(I_abs)I_abs was found that is not predicted by the theory. Nevertheless, this experimental approximation can be used in calculations in order to minimise the error.