Raman frequency shift induced by photorefractive effect on Fe–doped lithium niobate

We report on the observation of a time dependent frequency shift of the Raman modes in photorefractive Fe:LiNbO3. The origin of this shift is attributed primarily to the space charge field which builds up due to photo-induced charge transport by the excitation beam, and to the subsequent piezo-induced strain. This phenomenon can be regarded as the Raman analogous of the photorefractive effect, in which the space charge field is detected by an electro-optic variation of the refractive index. It should be possible therefore to analyze it using standard models for photorefractivity. In this paper, we verify this claim discussing its validity.