High harmonic photo-induced gratings in photorefractive media

Photo-induced index gratings can be recorded in photorefractive crystals. These gratings can be employed for applications in optical memory and spectral filters. It is known that the photo-induced index gratings in photorefractive media are not exactly sinusoidal, even though the optical intensity is sinusoidal. In other words, higher harmonic index gratings exist. We propose and demonstrate a novel double exposure scheme which removes the fundamental component and all higher odd-orders of the index grating. As a result, a volume index grating is obtained with a grating period of Λ/2, where Λ is the fundamental period