Self-enhanced accumulative recording of nonvolatile photorefractive holograms in LiNbO3:Fe:Mn

To enhance the recorded space-charge field and to suppress the scattering noise in the recording of photorefractive nonvolatile holograms in LiNbO3:Fe:Mn crystals, we propose and investigate a cyclic recording scheme by the repeat of a recording interval with the red pattern and the ultraviolet light and a followed post-exposure interval with ultraviolet light. The ultraviolet light used for the post- exposure not only excites more electrons into the shallower (Fe) centers to lead to faster and stronger recording for the next recording cycle, but also acts as an additional incoherent illumination to erase the initially developed scattering noise gratings. Furthermore, we have observed the self-enhancement and the self-depletion phenomena originated from the beam-coupling effect in the holographic recording. It shows that the highest diffraction efficiency available from the self-enhancement during both the recording and fixing phases may be twice as large as the lowest one from the self-depletion, and it is necessary to consider the arrangement of self-enhancement in the practical applications. As a result, such a self-enhanced accumulative recording has a great benefit for the increase of diffraction efficiency and the suppression of scatter noise, no additional equipment being needed. The detailed experimental results and corresponding theoretical analysis are given.