| Summary: | A series of pure congruent lithium niobate (LiNbO3, CLN) crystals were grown and directly polarized under different electric currents in the growth furnace. Their holographic properties were investigated from the ultraviolet to the visible range. The response time shortened, whereas the diffraction efficiency increased incrementally with the electric current. In particular, the response time of CLN polarized under 100 mA can be reduced by a factor of 10 with a still high saturation diffraction efficiency of about 40.8% at 351 nm. Moreover, its response speed improved by 60 times and 10 times for 473 and 532 nm laser, respectively. The light erasing behavior implies that at least two kinds of photorefractive centers exist in the crystals. Increasing the polarization current induces two pronounced UV absorption peaks and a wide visible absorption peak in CLN crystals. The diffusion effect dominates the photorefractive process and electrons are the dominant carriers. The possible mechanism for the fast photorefractive response is discussed. Increasing the polarization electric current is an effective method to improve the photorefractive response of LN crystal.
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