Procedure for recording multiple-exposure holograms with equal diffraction efficiency in photorefractive media

We report experimental results that demonstrate for the first time, to our knowledge, more than 20 holograms stored and recalled with equal diffraction efficiency in photorefractive LiNbO(3). A physical explanation for this new recording procedure is presented, and a comparison is made with previous exposure methods that shows an order-of-magnitude increase in diffraction efficiency with the order of exposure for optically erasable holograms. The procedure holds for recording times much less than the saturation exposure time.