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Novel technique for the characterization of photorefractive materials

A technique for real time direct measurement of both the amplitude and phase of photorefractive space charge fields during grating formation is presented. Photorefractive gratings are formed by the interference pattern of two intensity modulated beams. The two beams are single sideband modulated at the same RF frequency but are of opposite frequency shift. A detector tuned to the modulation frequency is used to monitor the time development of both the amplitude and phase of the photorefractive grating using a heterodyne detection scheme. This technique provides substantial dynamic range and the necessary sensitivity for the detection of refractive index changes as small as 10-8 and phase changes as small as 1 degree(s). Data is presented for the build-up of the amplitude and phase of the photorefractive space-charge fields. The photorefractive physical properties of these crystals including diffusion transport length, photovoltaic transport length, screening length, and the mobility free carrier lifetime product are determined.