NONLINEAR MULTIPLE-GRATING INTERACTION IN DIFFUSION-DOMINATED PHOTOREFRACTIVE MEDIA

Using a new model based on the so-called perturbational approach, we p resent a theoretical analysis of nonlinear multiple-grating interactio n in diffusion-dominated photorefractive materials. This process appea rs when more than one grating at a time is induced in a photorefractiv e crystal. The interaction is caused by the nonlinear terms in the ban d-transport equations, and it is highly dependent on the intensity rat ios of the writing beams. We show that, in a three-wave mixing scheme in which one reference beam and two nearly coincident object beams are incident upon a photorefractive crystal, one holographic grating is s trongly influenced by the presence of the other. It appears that highe r harmonic gratings, together with so-called sideband gratings, have a significant influence on the primary gratings. We show, for the first time to our knowledge, that in the transient case the temporal gratin g buildup exhibits a much more complex behavior compared with the line ar case, in which only one grating is present. We also show that in th e steady state one grating can experience everything ranging from tota l extinction to an enhancement of more than 50% when a second grating is induced. Our theoretical results are in good agreement with previou sly presented experimental results. (C) 1996 Optical Society of Americ a.