FEEDBACK-CONTROLLED PHOTOREFRACTIVE 2-BEAM COUPLING

We show that a certain phase feedback between output and input changes dramatically the characteristics of photorefractive two-beam coupling . The diffraction efficiency of the dynamic phase grating, eta, reache s 1 or 0 (depending on the feedback sign) within a finite time for a w ide range of experimental parameters. The spatial-temporal behavior of the wave amplitudes is strongly nonlinear and the grating fringes for eta=1 or 0 are bended but not tilted. The theory elucidates a number of empirical observations and reveals the great potential of active st abilization for applications.