Ce∶KNSBN晶体两波耦合动态过程研究

本文在非同时读出条件下,采用实时数据采集系统,实验研究了e偏振光写入Ce∶KNSBN晶体两波耦合动态过程,发现不同的写入光强比和写入总光强对晶体中两波耦合过程产生明显的影响;当He-Ne 632.8nm激光通过Ce∶KNSBN晶体时,光扇效应存在明显的写入光强阈值特性,其阈值约为20mW/cm2.依据实验结果对考虑光扇影响的耦合波方程进行了修正,其数值计算与实验结果基本符合.     

Ce:KNSBN光折变晶体两波耦合响应时间特性研究

在写入光分别为e光和o光时,实验测量了Ce:KNSBN晶体两波耦合响应时间与总写入光强、写入光强比和写入光夹角的关系,实验数据与理论拟合结果相吻合,并由晶体响应时间特性获得了晶体有效电光系数和有效光折变电荷密度参数.     

Ce∶KNSBN晶体写入光位置对两波耦合增益的影响

本文采用非同时读出条件下两波耦合实验装置,以532 nm的单频固体激光器为光源,在不同写入光夹角θ、抽运光的偏振方向与e偏振光的方向呈10°、信号光为e偏振光及不同信号光与抽运光光强比条件下,通过改变写入光在Ce∶KNSBN晶体内的不同位置研究其对两波耦合有效增益的影响。研究结果表明,在相同角度下写入光强比为1∶10,写入光在晶体内位置d=0.1 cm时最佳,有效增益达到最大。在最佳写入光位置,写入光强比为1∶10时,在写入光夹角为24°时两波耦合有效增益为最大。并对实验结果进行了理论拟合与分析。     

抽运光偏振态对晶体两波耦合增益的影响

采用非同时读出条件下晶体两波耦合实验装置,以532 nm单频固体激光器为光源,研究了抽运光偏振态对Ce: KNSBN晶体两波耦合有效增益的影响.结果表明:在信号光为e光且入射光夹角为30 °条件下,当抽运光偏振态与e光夹角为10 °时,有效增益最大;通过比较信号光打开与关闭条件下不同偏振态抽运光入射晶体时信号光及抽运光透射光强,分析得出最大增益存在的原因是偏振角为10 °时抽运光的o光分量很好的起到了擦除光扇的作用,抑制了光扇的发生,从而增益最大.取抽运光偏振态与e光夹角为10 °,研究入射光光强比对Ce: KNSBN晶体两波耦合有效增益的影响,结果发现随入射光光强比的增大,有效增益先增大后减小,光强比为1: 50时对应的增益最大为33.8.同时对研究结果进行了相应的物理解释.     

Cr:KNSBN晶体两波耦合及其图像存储

本文以He-Ne 632.8nm激光为写入光,在非同时读出条件下,实验研究了e偏振光写入Cr:KNSBN晶体两波耦合过程中信号光和泵浦光的透射光强随时间的变化,以及单束泵浦光的透射光强随时间的变化,实验结果表明,泵浦光损失的能量几乎全部转移到了信号光方向,基本不存在散射光;并以二值化图像作为物在晶体内进行了图像存储实验,其再现图像清晰,信噪比高,没有观察到扇形光的影响.     

优良全息光折变存储材料-双掺铌酸锂晶体

我们生长与后处理了一系列双掺铌酸锂晶体,通过光折变存储性能的测试,在这些晶体中,我们发现了三种双掺晶体:LN:Fe,Mg;LN∶Fe,In;LN∶Fe,Zn,它们具有优良的光折变存储性能,即高衍射效率(高达60～80;)、快光折变响应(比LN∶Fe 晶体缩短了一个数量级)、和强抗光散射能力(比LN∶Fe提高近两个数量级).我们还系统地研究了光强阈值效应与全息写入的关系以及全息写入与入射光强的关系,发现在光强阈值附近耦合强度有一最大值,从而提出了最佳写入光强的概念.另外,全息光栅热固定研究还显示,双掺铌酸锂晶体比单掺Fe的铌酸锂晶体具有更优良的热固定性质:快固定时间、高固定效率、长固定寿命等.     

掺杂LN晶体光折变效应及图象光存储特性

利用514.5nm和632.8nm波长的激光,研究了单掺杂Fe和双掺杂Ce∶Fe离子铌酸锂晶体的光折变二波耦合及光折变全息存储特性.实验结果表明生长态双掺杂Ce∶Fe与单掺杂Fe的LiNbO3晶体的光折变波耦合增益差异不明显,但双掺杂Ce∶Fe的LiNbO3晶体的图象存储和擦除特性明显得到改善.氧化态样品具有较大的透过率光谱范围和较好的图象存储质量;还原态样品具有较大的光折变二波耦合增益特性.     

外加磁场对掺铁铌酸锂晶体中折射率光栅擦除过程的影响

研究了外加磁场对掺铁铌酸锂晶体中折射率光栅擦除过程的影响.在写入和擦除过程中分别或同时外加磁场,测量了不同擦除光强下磁场对光栅擦除过程的影响.结果表明,外加磁场对折射率光栅擦除时间存在明显影响.在光栅写入或光栅擦除过程分别外加磁场时,光栅擦除时间增加;但是当在写入和擦除过程同时外加磁场时,光栅的擦除时间明显变短.擦除时间变化与擦除光强相关,擦除光强越弱,磁场对擦除时间的变化越明显.进一步的研究发现擦除时间的变化来自于磁场对铌酸锂晶体中等效暗电导的影响.以上实验结果显示,外加磁场可以成为掺铁铌酸锂晶体光折变光栅的调控手段.     

Ce:KNSBN光折变联合变换相关的研究

本文研究了Ce:KNSBN光折变联合变换相关,以Ce:KNSBN光折变晶体作为平方律转换器件,用波长为514.5nm的Ar+离子激光做写入光,在系统的傅里叶变换平面上放置光折变晶体记录输入靶物和参考物的联合变换功率谱,用632.8nm的He-Ne激光作为读出光,读出联合变换功率谱,输入到计算机进行处理,进而实现相关识别.实验研究了基于光折变晶体的传统联合变换相关器(PCJTC)和二元联合变换相关器(PBJTC)的识别能力.结果表明,PCJTC有着一定的相关识别能力,可实现靶物和参考物的相关识别,而采用了联合变换功率谱二值化后的PBJTC,其一级相关峰值较强而尖锐,中心直流零级峰相对减弱,并且有更大的相关信噪比,因此其相关识别能力也得到了一定的提高.     

Cu:KNSBN晶体生长及其光折变效应的研究

在KNSBN晶体中掺进CuO,采用硅钼棒作加热体,以Czochralski技术生长Cu:KNSBN晶体.以二波耦合光路,测试晶体的衍射效率和记录时间,计算折射率变化值Δn.Cu:KNSBN晶体的衍射效率,记录速度和折射率变化值皆高于Fe:LiNbO3晶体.尤其记录速度比Fe:LiNbO3晶体高一个数量级以上.测试Cu:KNSBN晶体位相共轭反射率R和自泵浦位相共轭反射率RC.Cu:KNSBN晶体的自泵浦位相共轭反射率RC值达到64;,是纯KNSBN晶体的二倍.以Cu:KNSBN晶体自泵浦位相共轭镜进行消畸变实验.实验结果表明:输出光波确系输入探测光波的位相共轭光波.     

大直径、高掺镁铌酸锂晶体的生长及其紫外光折变性能研究

我们生长了掺镁量分别为3.0mol;、5.0mol;、7.8mol;、9.0mol;的76mm高掺镁铌酸锂晶体,检测了这些晶体的生长条纹情况,并利用双光耦合配置测试了这些晶体在351nm紫外光下的光折变性能.从实验结果看,采用同成分共熔点铌锂配比的高掺镁铌酸锂晶体生长条纹比较多;虽然高掺镁铌酸锂晶体在可见光波段有很好的抗光折变能力,但是在紫外光下具有良好的光折变性能,可以作为优良的紫外光折变材料使用.同时,实验结果表明,掺镁量在5.0mol;的铌酸锂晶体具有最佳的紫外光折变性能.     

The Growth and Properties of K1-yLiyTa1-xNbxO3 Crystal

Potassium lithium tantalate niobate (K_1-yLi_yTa_1-xNb_xO₃, KLTN) crystals with tetragonal phase at room temperature were grown by the flux pulling method. Two-wave coupling energy transfer has been realized in this crystal. The two-wave coupling gain coefficient measured is 0.46 cm⁻¹, and the sign of the dominant carrier is positive. As compared with potassium tantalate niobate (KTN), the dielectric properties of KLTN changed significantly.     

Memory effect in the glass transition region of silicate glass based on light scattering data

The experimental results of the changes of the visible light scattered intensity after temperature jumps in the glass transition region of silicate glass were presented. The influence of the thermal prehistory on the height and location of the scattered intensity maximum was studied. The conditions corresponding to the maximum value of the scattered intensity were determined. The non-monotone character of the dependence of the limit height of the maximum as a function of the stabilization temperature was obtained. It was shown that the relaxation times of the increasing of the intensity considerably exceeded the structural relaxation times. These features were similar to the results obtained for the phosphate glass earlier. The universal character of the non-linear coupling of the laser irradiation with the glass structure formed in the process of development of the maximum intensity was found.     

Scx:Fey:Cuz:LN晶体的生长及非挥发性全息存储的研究

本文首次采用Czochralski法生长优质的Scx:Fey:Cuz:LN (x=0,1;, 2;, 3;, 3.5;, y=0.1;, z=0.06;)晶体.测试了晶体抗光致散射能力,以二波耦合光路测试晶体的衍射效率、写入时间和擦除时间,计算光折变灵敏度和动态范围.结果表明:Sc(2mol;):Fe:Cu:LN和Sc(3mol;):Fe:Cu:LN晶体抗光致散射能力比Fe:Cu:LN晶体高两个数量级以上,Scx:Fey:Cuz:LN晶体的写入速度、光折变灵敏度和动态范围等全息存储性能优于Fe:LN晶体.首次采用氪离子激光(482.0 nm,蓝光)作开关光,氦氖激光(632.8 nm,红光)做记录光,以Sc:Fe:Cu:LN晶体作为双光子全息存储记录介质,实现了双光子全息存储固定(非挥发性全息存储).     

Dynamic photorefractivity guided by single-pulse voltage

The dynamic photorefractivity in a cell with photoconducting orienting layers, filled with a nematic liquid crystal (LC) 6CHBT and a mixture of anthraquinone dyes AD1 and AD2, has been investigated. The single-pulse mode, in which the polarity and amplitude of a dc electric field applied to an LC cell are switched for a fixed time interval, has been used. The scheme of dynamic self-diffraction of low-power laser beams was used in the experiment. The dependences of the width and intensity of diffraction pulses on the bias and switching voltages have been investigated. It is established that the width and intensity of the diffraction pulse arising after initial voltage recovery depends also on the switching pulse width. At the optimal width of the control pulse, the diffraction efficiency increases by two orders of magnitude.     

Nematic Defects and Colloids as Photonic Elements

Birefringent structures in liquid crystalline fluids, such as colloidal assemblies or topological defects, show high potential for use as photonic elements. Here, we present a brief overview of two photonic phenomena originating from coupling light fields with complex birefringent nematic profiles: (i) the generation of vector laser beams from simple Gaussian beams by propagating light along nematic discliantions, and (ii) tunable photonic crystals from blue phase colloidal crystals conditioned by the different underlying symmetries of the particle lattice and the blue phase birefringence. The polarization profile of initially simple linearly polarized Gaussian beams is shown to change into a defect structure at distinct distances travelled along the disclination with the topological invariant (winding number) of the light field and nematic director distinctly coupled. Upon pulsed laser illumination, the nematic discliantions are also shown to split the light pulse into multiple intensity regions. Blue phase I face centred cubic colloidal crystals are shown as examples of tunable photonic crystals, where local band-baps can open by differently combining the symmetries of the two components, e.g. by changing the particle size. The spatial profiles of selected photonic bands in the blue phase colloidal crystals are shown, finding the particles and blue phase double twist cylinders as possible carriers of high-light-intensity regions.     

X-ray plane-wave diffraction effects in a crystal with third-order nonlinearity

The two-wave dynamical diffraction in the Laue geometry has been theoretically considered for a plane X-ray wave in a crystal with a third-order nonlinear response to the external field. An analytical solution to the problem stated is found for certain diffraction conditions. A nonlinear pendulum effect is analyzed. The nonlinear extinction length is found to depend on the incident-wave intensity. A pendulum effect of a new type is revealed: the intensities of the transmitted and diffracted waves periodically depend on the incidentwave intensity at a fixed crystal thickness. The rocking curves and Borrmann nonlinear effect are numerically calculated.     

基于NARX动态神经网络直拉硅单晶直径预测模型

直拉法在制备硅单晶的过程中存在机理假设多、多场耦合下边界条件不明确和化学变化交错且相互影响等问题,导致无法建立准确的机理模型用于硅单晶生长过程控制。针对此问题,本文以单晶炉拉晶车间的大量晶体生长数据为基础,基于互信息理论提出的最大信息系数(MIC)算法,对与晶体直径相关的特征参数进行分析,然后基于带外源输入的非线性自回归(NARX)动态神经网络,建立多输入单输出的等径阶段晶体直径预测模型,并对三台单晶炉拉晶数据进行直径预测,预测的平均均方误差值为0.000 774。最后将NARX动态神经网络同反向传播(BP)神经网络进行对比分析,验证了该模型的优越性。结果表明,NARX动态神经网络为晶体直径的控制提供了一种更准确的辨识模型。