The dependence of self-pumped photorefractive two-beam coupling in $\mathrm{Fe}:{\mathrm{KNbO}}_3$ with crystal angle has been measured at $532\mathrm{nm}$ for the $a$-$c$ and $b$-$c$ crystal planes using a combination of oil immersion and relay imaging. A significant deviation between existing theory and experiment is found for large crystal angles. We propose this is due to a highly anisotropic effective charge trap density in $\mathrm{Fe}:{\mathrm{KNbO}}_3$ of almost two orders of magnitude variation with crystal angle in the $a$-$c$ plane.

• Received 4 January 2006

DOI:https://doi.org/10.1103/PhysRevB.73.174102