Recording of high harmonic gratings in photorefractive media

We have proposed and demonstrated a novel scheme for the recording of high harmonic index gratings in photorefractive crystals. By using a double exposure in a Mach Zehnder interferometer with a dual input port, we demonstrated the recording of a second harmonic index grating with a period of /spl lambda//2 in a photorefractive KNaSrBaNb/sub 2/O/sub 6/:Mn (KNSBN:Mn) crystal.