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Photorefractive (PR) gratings have been induced by 442-nm light illumination in Bi4Ge3O12 single crystals doped with Cr impurities. In undoped material no grating was detected. The PR response is likely in the range 300–500 nm, for photoconduction has been observed in this interval in both undoped and Cr-doped samples. Cr ions act mainly as traps, the donors being intrinsic defects of the undoped material. The light-induced writing, τg, and erasure times, τb, are in the range of some minutes (τg = 1.1 min, τb1 = 1.3 min, τb2 = 3.4 min; I0 = 1.6 mW/cm2). Under dark conditions the erasure time, τbd, is of the order of several hours (τb1d = 17.8 min, τb2d = 365.8 min; I0 = 0.8 mW/cm2). The magnitude of the diffraction efficiency observed is approximately 0.5% with no applied electric field, which corresponds to a refractive-index change of Δn0 = 1.89 × 10−5. When an electric field is applied, a transient behavior is observed. To explain this fact we have assumed that compensating charges that erase the PR grating are present.
© 1988 Optical Society of America
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