Photorefractive response in the case of a high interference-pattern contrast

A theoretical investigation is reported of the response of a photorefractive crystal to an interference pattern $I_0[1+m \exp\{i(qx-\Omega t)\}]$ with a sufficiently high contrast $\vert m\vert$. Expressions are obtained for the second harmonic of the space charge field. Correction terms of the order of $m\vert m\vert^2$, leading to saturation of the first harmonic of the field, are formed for different resonant and nonresonant recording mechanisms.