Space charge fields in photorefractive crystals in the presence of direct current and alternating current fields: A new resonance

It is shown theoretically that the space charge field generated by two-wave mixing in a photorefractive crystal may have a resonant response when a de field and a sinusoidal ac field are simultaneously applied. Resonance occurs when the frequency of the ac held is equal to the eigenfrequency of the space charge wave determined by the de voltage. Analytical expressions are derived for the magnitude of the space charge wave and the optimum ratio of the ac to de field is determined. The enhancement of the space charge field is shown to be considerably higher than that obtained by a nonresonant method utilizing a sinusoidal ac field alone. Under optimum conditions the maximum space charge held available is equal to mE(q)/2 root 2, where m is the modulation of the interference pattern and E(q) is the saturation field. (C) 1996 American Institute of Physics.