Tunable frequency shift of photorefractive oscillators

We report on an experimental study of the self-frequency detuning in wave mixing oscillators with the photorefractive barium titanate crystal. We show its dependence on a dc electric field on the crystal, optical phases in the oscillator cavity, and light intensity in the crystal. This resolves many aspects of previously observed and unexplained self-frequency detuning effects with similar oscillators and indicates the existence of an internal electric field in the mixing crystal.