We present the first complete theoretical model that describes the formation of the space-charge field in a photorefractive material that is exposed to a sinusoidal ac electric field with a dc offset and a running light-interference pattern. The model is complete in the sense that it is valid for all time scales and hence also covers situations in which the well-known period-averaging technique is inapplicable. For large temporal frequencies of the ac electric field the solution is shown to converge with that obtained from the period-averaging technique. It is shown that by imposing a running interference pattern and a sinusoidal ac electric field simultaneously, it becomes possible to enhance certain frequency components selectively. Experiments are performed to confirm the theoretical findings, and good agreement is obtained.
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