Measurement of the spatial phase shift in high-gain photorefractive materials

The correct determination of the spatial phase shift ${\varphi }_p$ in photorefractive materials is crucial to the proper characterization of novel materials. It is shown that the grating translation techniques commonly used for the measurement of ${\varphi }_p$ need to be reevaluated for high-gain materials. Strong energy and phase coupling leads to nonuniform slanted gratings, which result in an apparent dependence of the phase shift of the beam ratio and the optical polarization. A revised theory is presented, and analytical solutions are obtained for the special case of ${\varphi }_p\cong \pi /2$. Numerical solutions for arbitrary ${\varphi }_p$ are in good agreement with measurements in a photorefractive polymer.