Abstract
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.
Highlights
Photorefractive (PR) materials have attracted considerable attention due to their interesting applications, such as three-dimensional (3D) displays, holographic data storage, image amplification and optical phase conjugation [1,2,3,4,5]
Doping elements with variable valences is an effective way to induce extrinsic defects with different energy levels for improving response speed, such as Fe, Mn, Cu, Ce, V, and Mo [15,16,17,18], the response time still cannot satisfy the requirements of real-time dynamic 3D holographic displays
We report on the improvement in photorefractive response speed of CLN crystals by polarizing them under different electric currents and analyzing the mechanism based on the model concerning Q polarons
Summary
Photorefractive (PR) materials have attracted considerable attention due to their interesting applications, such as three-dimensional (3D) displays, holographic data storage, image amplification and optical phase conjugation [1,2,3,4,5]. Since the most fascinating application of updatable holographic Some disadvantages, such as low stability and the need of high electric fields to obtain excellent photorefraction properties, limit their practical applications [4,5,9,10]. Crystals 2017, 7, 368 efficiency and high data-storage density, but it cannot realize real-time dynamic hologram displays due to the slow response speed (several minutes) [12,13]. Doping elements with variable valences is an effective way to induce extrinsic defects with different energy levels for improving response speed, such as Fe, Mn, Cu, Ce, V, and Mo [15,16,17,18], the response time still cannot satisfy the requirements of real-time dynamic 3D holographic displays. It should be easier to study this issue in pure congruent LN crystals (CLN) without extrinsic defects
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