The persistent hidden photorefractive gratings were produced in a homeotropic C_(60)-doped liquid crystal cell by two 488 nm writing beams. The persistent gratings can be hidden and revealed by turning off and on an incident laser beam at 488, 532, or 632 nm at any incident angle in the presence of a dc electric field or by turning off and on the applied dc electric field in the presence of an illuminating beam. These hidden gratings can be rejuvenated after keeping as long as several hours in the presence of the dc electric field. The possible underlying mechanism involving the surface-mediated effect and the bulk-mediated Carr-Helfrich effect is proposed. Consistent with this mechanism, the diffraction efficiency of the hidden gratings shows a dependence on the power of the illuminating beam, and the hidden grating can be revealed by applying a higher voltage without any illumination.
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