An effective technique of direct recording with UV beams for high sensitivity during nonvolatile holographic storage in LiNbO<sub>3</sub>:Ce:Cu crystals is proposed and investigated. Just contrary to the usual recording scheme in which red beams are used for writing while UV light is for sensitizing, in this paper two mutual coherent UV beams of 365 nm are used to directly record gratings in two trap centers simultaneously with illumination of a red light, and the finally remained grating in deeper centers is insensitive to red light for further readout. High sensitivity of 0.31 cm/J is gained in our experiments, which is about two orders of magnitude greater than that gained by the conventional technique. A unique characteristic inherent in this recording technique which is in phase between two gratings recorded in two trap centers is demonstrated and its function of improving diffraction efficiency is analyzed.

© 2005 Optical Society of America

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