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We present several new characteristics of beam fanning in a bulk sample of Bi12SiO20 with a dc electric field applied to it. Significant dependence of the beam fanning on the polarization state of the incident laser beam is observed. Moreover, the fanning light experiences a spontaneous frequency shift with respect to the incident light that ensures maximum beam coupling, because of which the fanning itself can exist.

We propose a theoretical model for the recently reported anomalously long decay of a space-charge field that was resonantly excited in a photorefractive sillenite crystal [Phys. Rev. Lett. 79, 67 (1997)]. The model is based on the conventional concept of charge transfer and does not require excessively large values of the quality factor for space-charge waves. The effect in question is qualified as a critical slowing of the relaxation process as the threshold of optical oscillation is approached.

A new subharmonic regime in photorefractive bismuth silicon oxide has been discovered by the use of the running-grating technique. In this regime the subharmonic grating splits into two gratings that are angularly tilted with respect to the fundamental grating. These observations necessitate an extension of previously proposed theories.