Study On Polarization Process And Bridgman Growth Of Lithium Niobate Crystals

Lithium niobate?LiNbO₃,LN?is a kind of multi-functional artificial crystal material with excellent comprehensive performance.It has a wide range of applications in holographic display,holographic storage,acousto-optic,piezoelectric,etc.However,the low photorefractive response speed and poor optical uniformity have limited the application of real-time dynamic 3D holographic display and industrial growth with large-size.In response to the above problems,this paper carried out the following work:First,through high temperature secondary sintering,the congruent lithium niobate polycrystalline material is synthesized.Using Czochralski method succeed in growing series of congruent LN crystals,the half-height width of the double rocking curve is about 17 ?.By changing the polarization process parameters,the response speed of photorefractive can be adjusted.The results show that the photorefractive response speed and saturation diffraction efficiency of LN are effectively improved through enhance the polarization current.Especially when the polarization current is increased to 100 m A,the response speed is increased by 10 times at 351 nm.The response time is shortened to 1.4s,while the diffraction efficiency is maintained at 40.8%.The response speeds at 473 nm and 532 nm are increased by 60 times and 10 times respectively.The results of light erasing studies indicate that there are at least two photorefractive centers in the crystals,and the photorefractive mechanism is mainly diffusion.The mechanism by which the polarization current changes the photorefractive response speed is described from the perspective of intrinsic defects.Secondly,wet-chemical methods are used to synthesize different concentrations of magnesium-doped lithium niobate?LN: Mg?polycrystalline materials.By optimizing the crystal growth process of the Bridgman method,2-inch highly magnesium doped LN crystals with high-quality are successfully grown along the c-axis?001?direction,whose half-height width of the double rocking curve is 8? and the transmittance can reach higher than 70%.Compared with LN crystals,when the Mg-doped concentration reaches 5mol%,its OHabsorption peak moves from 3484cm^-1 to 3534.7cm^-1,indicating that 5mol% exceeds the threshold concentration of Mg.The results of the birefringence gradient method show that the refractive index gradient of extraordinary light in LN doped with 5mol% Mg is 2.5 × 10^-5 / cm,which indicates that the 2-inch LN highly doped with magnesium who possess high optical homogeneity is successfully grown by the Bridgman method.On this basis,we explored the growth research of indium-molybdenum double-doped LN crystals by Bridgman method.