铌酸钾锂晶体的生长与性能

使用坩埚下降法成功生长了尺寸为φ10mm50mm、四方钨青铜结构、透明铌酸钾锂晶体,讨论了引起晶体开裂的主要原因,研究了该晶体的光透过性能和介电性能,室温下该晶体的介电常数ε33=127,ε11=376,居里温度为380°     

铌酸钾锂晶体的生长研究

首次使用坩埚下降法生长了蓝光掊频晶体铌酸钾锂K₃Li_2-xNb_5＋xO_15＋2_x（0＜x＜0．5）,探讨了该晶体的最佳生长条件,包括组份选择、原料处理、炉温控制、温场设计等,成功地生长出直径10mm、长度25mm的透明KLN晶体．     

铌酸钾锂晶体的生长技术

铌酸钾锂被认为是目前综合性能指数最高的非线性光学晶体,在半导体二极管蓝激光倍频方面有广阔的应用前景。本文综述了用于蓝光倍频的铌酸钾锂晶体生长研究进展,比较了不同生长方法的优缺点,报道了我们在该晶体坩埚下降法生长研究方面的最新成果。     

掺铜铌酸钾锂晶体光折变效应的研究

在铌酸钾锂晶体中掺进ＣｕＯ,采用Ｃｚｏｃｈｒａｌｓｋｉ法生长Ｃｕ：ＫＬＮ晶体。测试Ｃｕ：ＫＬＮ晶体红外透射谱,研究ＯＨ＾－吸收峰发生红移的原因。以二波耦合光路测量Ｃｕ：ＣＬＮ晶体的光折变擦除曲线,计算擦除时间和光电导,研究Ｃｕ：ＫＬＮ晶体的光折变性能。     

掺镁铌酸钾锂晶体的生长与介电特性

首次用提拉法生长了K3Li2 Nb5O15∶Mg晶体 ,在 10～70 0K的温度范围内 ,研究了该晶体的c、a方向片的介电温度特性 ,测量了频率在 5× 10 2 ～ 5× 10 8Hz范围内介电常数的频率依赖关系。结果表明除了在 62 3K附近有铁电 -顺电相变以外 ,还在 80K左右存在铁电 -铁电相变 ,其介电弛豫频率约为2 5 0MHz左右。     

聚合物前驱体法制备铌酸钾锂粉体的研究

采用聚合物前驱体法制备了KLN纳米陶瓷粉体。研究了不同pH值、不同柠檬酸与金属离子物质的量比（CA：M^n＋）以及不同退火温度对K-Li-Nb溶胶稳定性以及粉体组成的影响。实验结果表明：K-Li-Nb凝胶热分解过程分为3个阶段，KLN的生成温度在590～620℃左右：当柠檬酸与金属离子物质的量比（CA：M^n＋）为3：l，前驱体溶液pH值控制在6～10内可以得到均匀透明的溶胶。pH=10的前驱体凝胶在850℃下煅烧后得到较纯的KLN纳米陶瓷粉体。     

掺铜铌酸钾锂晶体光析变效应的研究

在铌酸钾锂 (KLN)晶体中掺进CuO ,采用Czochralski法生长Cu∶KLN晶体。测试Cu∶KLN晶体红外透射谱 ,研究OH- 吸收峰发生红移的原因。以二波耦合光路测量Cu∶KLN晶体的光析变擦除曲线 ,计算擦除时间和光电导 ,研究Cu∶KLN晶体的光折变性能     

铌酸锂晶体的结构与性能关系研究

在实验测定的结晶学数据基础上，键价模型和化学键方法都被应用于定量或定性的研究铌酸锂晶体的物理性质，例如介电性质（包括折射指数n0和二阶非线性光学系数dij）、居里温度Te和自发极化率Ps。在前期工作中提出的Nb^5＋位依赖Li^＋位敏感的模型已成功地应用于铌酸锂晶体多种物理性质的研究。结果显示，其物理性质对晶体组成有强烈的依赖性。Nb^5＋位对于铌酸锂晶体的机械性质具有很强的影响；而Li^＋位也与晶体的介电性质密切相关．同时Li^＋位也是对＋1～＋5价不同掺杂剂敏感的晶格位置。     

单晶铌酸锂薄膜光波导的制备研究

为了优化单晶铌酸锂薄膜光波导的性能,研究了基于单晶铌酸锂薄膜材料的光波导刻蚀工艺。虽然Ar⁺物理刻蚀能够达到最高95 nm/min的刻蚀速率,但难以获得光滑的波导侧壁,且以Cr作为掩膜的刻蚀选择比为1∶1,这意味着较差的选择性使其难以实现铌酸锂的深刻蚀。而采用反应离子刻蚀(RIE)得到的刻蚀速率较低,但是以Cr作为掩膜的刻蚀选择比能够达到6∶1以上,同时能够获得光滑、陡直的侧壁形貌。最终在450 nm厚度的单晶铌酸锂薄膜上,采用RIE制备了宽度为4μm、高度为370 nm的脊型光波导,并以端面耦合的方法进行测试,得到该波导的传输损耗约为5.2 dB/cm。     

Ce:Eu:LiNbO3晶体制备及光折变性能

为了昨到光折变性能优良的晶体材料，在LiNbO3中掺进CeO2和Eu2O3，生长Ce:LiNbO3和Ce:Eu:LiNbO3单晶体，对晶体进行极化和氧化还原处理，并利用XRD、UV-VIS及二波耦合光路测试了晶体的晶格常数、吸收光谱、指数增益系数和响应时间。结果表明，Ce:Eu:LiNbO3晶体的晶格常数比Ce:LiNbO3晶体小，其吸收边比CeLiNbO3晶体红移更多，指数增益系数比Ce:LiNbO3晶体大，而响应时间比Ce:LiNbO3晶体的要短，Ce:Eu:LiNbO3是优良的光折变晶体材料。     

光折变Bi12SiO20晶体中的波耦合性质

研究在光折变Bi12SiO20晶体中二波耦合扩散全息记录的信号光能量增益和偏振态改变。在3种制备可得的晶体切割面上给出任意光栅取向的能量和偏振态耦合量的取值范围,分析了信号光能量增益和偏振态改变量分别达到最大值时各向同性和各向异性耦合的作用,此外研究旋光效应，压电及弹光效应在3种晶体切割面上对矢量波耦合的影响。     

Transport properties of Nd1.85Ce0.15 δ single crystals: The narrow-band model

The anisotropy of the resistivity and thermoelectric power (TEP)S of Nd_1.85Ce_0.15CuO_4?δ single crystal (T _c =17 K) has been investigated. In the temperature rangeT _c <T<300 K the ratioρ _c/ρ_ab≈10⁴ and the dependencesρ _ab (T) andρ _c (T) change from quadratic to linear atT～200 K. The dependencesS _ab (T) andS _c (T) reach a maximum atT>T _c and then decrease almost linearly with increasing temperature, changing sign from positive to negative nearT～ 150 K. The features of the resistivity and TEP temperature dependences (the lawρ∝T ² changing toρ∝T, the change in the sign of S with temperature, and the low TEP anisotropy at largeρ anisotropy) have been interpreted in the framework of the narrow-band model.     

Preparation and scintillation properties of YCl3:Ce crystals

Ce³⁺-activated YCl₃ crystals have been grown by the Bridgman-Stockbarger method, and their scintillation properties have been investigated. The luminescence spectrum of YCl₃:Ce has a complex character and consists of two overlapping peaks at 390 and 410 nm, characteristic of Ce³⁺ luminescence. The light output of YCl₃:Ce as a function of Ce³⁺ concentration has a maximum at 1 mol % Ce³⁺. Original Russian Text ? V.L. Cherginets, T.V. Ponomarenko, L.N. Trefilova, N.V. Rebrova, N.N. Kosinov, V.D. Alekseev, O.V. Zelenskaya, 2009, published in Neorganicheskie Materialy, 2009, Vol. 45, No. 8, pp. 1017–1020.     

高掺镁LiNbO3晶体抗光折变性能研究

在LiNbO3中掺进MgO以提拉法生长Mg(1mol%)LN,Mg(3mol%)LN,Mg(5mol%)LN,Mg(7mol%)LN,和Mg(9mol%)LN晶体.改进晶体生长工艺条件,解决了在生长中出现的脱溶,散射颗粒,生长条纹等缺陷.生长出高质量高掺镁LiNbO3晶体.测试MgLiNbO3晶体的红外光谱,当Mg2+的浓度达到或超过阈值浓度的MgLiNbO3晶体,OH-吸收峰移到3535cm-1,晶体抗光损伤能力比LiNbO3晶体提高两个数量级以上.测试MgLiNbO3晶体的倍频性能(相位匹配温度,倍频转换效率)MgLiNbO3晶体的相位匹配温度随Mg2+浓度的增加而改变,Mg(5mol%)LN,晶体的相位匹配温度达到116℃,Mg(9mol%)LN晶体在室温附近.     

Spatial self-filtering using photorefractive and liquid crystals

Abstract

In a paper by Möbus et al. a method for defect enhancement by spatial self-filtering using B₁₂SiO₂₀ (BSO) in the Fourier plane of an optical processor was presented. In periodic structures the unwanted sharp peaks in the Fourier plane have to be removed in order to enhance defects. In this paper we describe sub-micron defect detection by self-filtering with BSO in detail and compare the photorefractive method with a new very promising filtering approach using optically addressed spatial light modulators (OASLM). Interesting results especially for chromium-on-glass masks, CCD arrays and memory chips were obtained with a simple set-up. In addition numerical techniques will be examined.     

Photoelectroluminescence of ZnS:Mn crystals

Data on the room-temperature photoelectroluminescence of Mn-activated zinc sulfide crystals are presented. The differential luminescence spectrum demonstrates that the combined excitation leads to a strong buildup of the Mn-related emission.     

Recent developments in the growth and characterization of potassium lithium niobate (KLN) crystals for direct doubling of semiconductor lasers

This paper reports the successful growth of crystals of the potassium lithium niobate (KLN) family having a non-centred tungsten bronze structure. Crack free crystals up to 20 mm in diameter by 30 mm in length have been grown reproducibly by the top-seeded solution growth (TSSG) method from K+ and Li+ rich solutions. These crystals form solid solutions in which both the structural and optical properties vary with composition. Birefringence measurements show that KLN crystals may be non-critically phase matched for second harmonic generation in the wavelength range 1050 nm to 820 nm at room temperature, depending on composition. The ability to tune the optical properties in this way makes KLN an ideal candidate for direct doubling of semiconductor lasers. © 1998 Chapman & Hall     

Convergence of backward-error-propagation learning in photorefractive crystals

We analytically determine that the backward-error-propagation learning algorithm has a well-defined region of convergence in neural learning-parameter space for two classes of photorefractive-based optical neural-network architectures. The first class uses electric-field amplitude encoding of signals and weights in a fully coherent system, whereas the second class uses intensity encoding of signals and weights in an incoherent/coherent system. Under typical assumptions on the grating formation in photorefractive materials used in adaptive optical interconnections, we compute weight updates for both classes of architectures. Using these weight updates, we derive a set of conditions that are sufficient for such a network to operate within the region of convergence. The results are verified empirically by simulations of the xor sample problem. The computed weight updates for both classes of architectures contain two neural learning parameters: a learning-rate coefficient and a weight-decay coefficient. We show that these learning parameters are directly related to two important design parameters: system gain and exposure energy. The system gain determines the ratio of the learning-rate parameter to decay-rate parameter, and the exposure energy determines the size of the decay-rate parameter. We conclude that convergence is guaranteed (assuming no spurious local minima in the error function) by using a sufficiently high gain and a sufficiently low exposure energy per weight update.     

The dynamics of double reversal of wave fronts in photorefractive crystals

Averaged equations are derived describing the process of relaxation of reversed waves in the case of complex light fields in a scheme of double reversing mirror. Qualitative agreement between the experimentally derived and calculated time dependences is obtained for an optical circuit employing a Bi₁₂TiO₂₀ crystal.