双轴晶体有效非线性系数的准确表述

本文介绍计算双轴晶体二阶有效非线性系数的严格理论,适用于双轴晶体非线性光学频率变换器件的设计。     

Optical frequency conversion in quasi-phase-matched stacks of nonlinear crystals

We present a quantitative theory of nonlinear frequency conversion in stacks of crystals where the phase mismatch due to dispersion is compensated by changing the sign of the nonlinear coupling coefficient in successive crystals-a method first proposed by Armstrong et al. We include pump depletion in our calculations of the second harmonic generation and sum and difference frequency generation. We start with ideal stacks in which the crystal lengths are tailored to achieve perfect phase compensation. When the conversion in each coherence length is small, all crystal lengths tend to equal the coherence lengthpi/Deltak. Frequency conversion in such stacks is well approximated by that in an equivalent phase-matched crystal with the nonlinear coupling coefficient reduced by a factor of2/pi. The effect of systematic as well as random departures in crystal lengths are studied with special attention to the evolution of the relative phase. We show that with appropriate choice of the signs of the nonlinear coupling coefficient in various crystals, high efficiency frequency conversion should be possible using practically any sufficiently large set of nonlinear crystals. The theory of second harmonic generation in periodic stacks and in rotationally twinned crystals of zinc-blend structure is described in detail.     

一种双轴向列相液晶两体势模型的标准化形式

研究刘红等提出的液晶双轴向列相两体势模型,将该模型两体势转化成标准形式。据此,可以清楚地看出它的色散力近似本质,确定势参数的取值范围,并对双轴向列相的研究进行了展望。     

Hybrid mode phase matching and effective nonlinear coefficient forsecond harmonic generation in biaxial waveguides

Phase matching between fundamental and second harmonic hybrid guided modes in nonlinear biaxial planar waveguides is determined for the first time based on principal axes orientations of the film, substrate, and cover. We have derived an expression for the effective nonlinear coefficient D_eff of hybrid modes in a biaxial waveguide and have calculated this coefficient numerically along the effective index phase match loci for these modes supported by a POM waveguide surrounded by isotropic media. The optimum phase matching orientations are determined for a fixed waveguide thickness. Dispersion of the principal indexes is considered     

新型铁电液晶的非线性光学性质的研究

详细研究了两种新型铁电液晶的非线性光学性质，液晶分子倾斜角θｔ、色散折射率，双折射率，双轴折射率和非线性光学系数各分量ｄｉｊ，两次谐波信号强度受外加电场及温度的影响，并分析了液晶分子结构与非线性光学性质的关系。     

常用双轴晶体连续调谐倍频时的相位匹配特性

本文讨论了常用双轴晶体ＫＴＰ、ＬＢＯ、ＫＮ在基频光波长连续调谐时的倍频相位匹配特性，给出了这三种晶体在不同波长倍频时的最佳相位匹配角的有效倍频极化系数，并纠正了以往计算中的不正确作法。     

无热致静态位相延迟、单块晶体结构的KNbO3和KTP电光开关

分析表明,当光在双轴晶体中波矢沿着某些特定方向传播时,不会表现出一阶热致静态位相延迟,这个方向暂时被称为晶体的无热致静态位相延迟光传播方向（ＮＴＳＰＲ方向）。根据前人发表的相关数据,采用适当近似,求得ＫＮｂＯ３的ＮＴＳＰＲ方向是（９０°,９０°±５０．１９°,５０．１９°）,ＫＴＰ的ＮＴＳＰＲ方向是（９０°±３０．７８°,９０°,３０．７８°）,并分别讨论了这两种晶体在这些方向的电光品质因数ηｅ,结果表明,利用某些双轴晶体ＮＴＳＰＲ方向大的电光品质因数制成的新型、单块晶体结构电光开关,不需要温控,而且,器件本身的通光长度可以做得更短。     

双轴晶体KTiOPO_4的多频率变换

1.双轴晶体KTiOPO_4(KTP)由于其优良的非线性光学性能而受到普遍重视，但一般仅限于在一个通光方向上获得一种非线性光学过程。考虑到双     

Measurement of Crystal Impedances at Low Levels

It is very important to know the impedances of crystal dilodes when constructing circuits such as mixers and detectors in which the crystals are used. It is always difficult to measure these impedances due to the nonlinear characteristics of the crystals but it is most difficult to make the measurements at minimum levels at which the crystals operate, since with such methods as the slotted line, the detector must operate at a still lower level to obtain the required probe decoupling. Thus, since the load whose impedance is being measured is itself a crystal operating at its minimum level, it is practically impossible to obtain a detector with sutlicient sensitivity to make the measurement. Crystal impedances at these minimum levels are of utmost importance as it is here that optimum matching is essential for maximum sensitivity. This paper describes practical tectilques which use only standard equipment to measure crystal impedances at low levels. The detector used is a crystal of the same type as that being measured. The method is capable of precise results and good measurements can be obtained at low levels with little more effort than is normally required in making careful impedance measurements.     

KTP晶体光参量过程的相位匹配

讨论了双轴晶体中参量过程的角度匹配计算方法,计算了KTP晶体对于355、532nm和1064nm波长泵浦的光参量过程的角度匹配曲线;对于三个主平面内的Ⅱ类相位匹配曲线的特点作了分析和讨论。实验验证了532nm波长泵浦的光参量过程,在X-Z平面内的Ⅱ类相位匹配角度值与理论计算的结果一致。     

PPLN准相位匹配技术在蓝绿激光器及中红外OPO中的应用进展

以PPLN、PPMgLN、PPKTP等为代表的周期极化工艺的成熟,极大地促进了准相位匹配技术的发展,拓宽了非线性晶体应用范围,大大提高了频率转换效率。周期极化晶体与其它非线性晶体结合,利用倍频、差频、混频、OPO等技术是实现激光波长拓宽的一种非常有效的手段。本文阐述了QPMPPLN在蓝绿激光器及中红外OPO的应用进展,展望了PPLN的应用发展趋势。     

Numerical calculation of the effective second-order nonlinearcoefficient along collinear phase-matching directions inside nonlinearcrystals in three-wave interaction

In this work, we present the first numerically calculated values of the second-order nonlinear coefficient D_eff along collinear phase-matching directions inside the biaxial crystal. We have demonstrated our results using KTP in optical parametric generation. Our results are in agreement with recent experimental data. The theoretical approach presented here is a simple and generalized method which encompasses H. Ito's and B. Wyncke's works     

基于周期极化晶体的QPM-SHG技术发展及其应用

随着新型高质量的非线性晶体的出现,准相位匹配技术成为非线性频率变换的最有效的方法。从周期极化晶体准相位匹配二次谐波发生器（QPM-SHG）的基本原理出发,简要介绍了实现周期极化晶体的方法和技术,总结了准相位匹配技术在光子学微结构晶体材料和波导材料中的最新研究进展和发展趋势,展望了用微结构波导QPM-SHG实现飞秒光纤光源的发展应用前景。     

Design of a Multistep Phase Mask for High-Energy Terahertz Pulse Generation by Optical Rectification

A new scheme for generating high-energy terahertz (THz) pulses based on using a multistep phase mask (MSPM) is suggested and analyzed. The mask is placed on the entrance surface of the nonlinear optical (NLO) crystal eliminating the necessity of the imaging optics. In contrast to the contact grating method, introduction of large amounts of angular dispersion is avoided. The operation principle of the suggested scheme is based on the fact that the MSPM splits a single input beam into many smaller time-delayed “beamlets,” which together form a discretely tilted-front laser pulse in NLO crystal. The analysis of THz-pulse generation in ZnTe and lithium niobate (LN) crystals shows that application of ZnTe crystal is more preferable, especially when long-wavelength pump sources are used. The dimensions of the mask’s steps required for high-energy THz-pulse generation in ZnTe and LN crystals are calculated. The optimal number of steps is estimated, taking into account individual beamlet’s spatial broadening and problems related to the mask fabrication. The proposed method is a promising way to develop high-energy, monolithic, and alignment-free THz-pulse sources.     

5ps紫外超短光脉冲产生技术

描述了采用国内新型高效的二倍频晶体ＫＴＰ和四倍频晶体ＬＡＰ建立起来的一套稳定可靠的１．０６μｍ脉冲激光四倍频系统，通过计算机模拟确定了运行参数的最佳值，从而使谐波器件的转换效率提高，另外还分析了失配角Δθ，光功率密度等因素对倍频效率的影响。该系统产生的超短紫外光脉冲对Ｘ光条纹相机的动态参数及带时标的条纹相机的研究具有重要意义。实验测得最短的紫外光脉冲宽度为５ｐｓ     

Improved second-harmonic generation by selective Yb ion doping in anew nonlinear optical crystal YCa4O(BO3)3

We describe experiments characterizing a new nonlinear optical crystal, YCa₄O(BO₃)₃ (YCOB). This crystal has a number of advantages over other commonly available nonlinear optical crystals. It has a higher nonlinear coefficient than KDP, can be fabricated to large sizes (~3-in diameter, 8-in length), and has a high damage threshold. Moreover, this new nonlinear optical crystal is nonhygroscopic, has good optical quality and mechanical properties, allowing easy optical polishing. This crystal, YCa₄ O(BO₃)₃, commonly termed YCOB, is one of a family of new nonlinear crystals, the oxyborates, that include RECa₄O(BO₃)₃ (RE=La³⁺, La ³⁺, Y³⁺, Sm³⁺, Gd³⁺, Er³⁺, and Nd³⁺). In this paper, we also successfully demonstrate a technique for improving the nonlinear optical properties of this crystal. This technique, ion substitution, has previously had limited success with other crystal hosts. However, the inclusion of yttrium in YCOB provides the opportunity to exploit this technique. Yb³⁺, which has larger mass, but approximately the same atomic size as Y³⁺ can be substituted into the crystal structure without introducing stress and nonuniformities. A systematic investigation of the linear and nonlinear characteristics of several crystals doped with various levels of Yb demonstrate that selective substitution of Yb in YCa₄O(BO₃)₃ improves the second-harmonic conversion efficiency by increasing the optical nonlinearity     

双轴晶体主平面上倍频的相位匹配

从折射率椭球方程和折射率椭球面出发，讨论光束在双轴晶体中传播及偏振的特性、主平面倍频共线相位匹配（PM）问题，得到了双轴晶体主平面内激光所有可能PM倍频的8种偏振组合及其相应的PM角公式、有效非线性（NL）系数deff的一般表达式。结果表明：得到的公式简单，可大大简化PM参数计算及优化设计；折射率椭球面是单层曲面，比双层的折射率面简单；基于折射率椭球面寻找所有可能PM的类型、偏振组合的方法物理图像简明，易于理解，大大降低了双轴晶体PM问题分析的难度。     

Properties of second harmonic generation in nonlinear optical crystals CsLiB_6O_(10) and K_2Al_2B_2O_7

1 Introduction In recent years short wavelength coherent radiation lying in th blue and UV range has attracted wide attention for a variety o applications, including laser printing, undersea communicatio etc. In view of this, several studies of nonlinear-…     

Organic Phenolic Configurationally Locked Polyene Single Crystals for Electro‐optic and Terahertz Wave Applications

We investigate a configurationally locked polyene (CLP) crystal 2‐(3‐(4‐hydroxystyryl)‐5,5‐dimethylcyclohex‐2‐enylidene)malononitrile (OH1) containing a phenolic electron donor, which also acts as a hydrogen bond donor. The OH1 crystals with orthorhombic space group Pna2₁ (point group mm2) exhibit large second‐order nonlinear optical figures of merit, high thermal stability and very favorable crystal growth characteristics. Higher solubility in methanol and a larger temperature difference between the melting temperature and the decomposition temperature of OH1 compared to analogous CLP crystals, are of advantage for solution and melt crystal growth, respectively. Acentric bulk OH1 crystals of large sizes with side lengths of up to 1 cm with excellent optical quality have been successfully grown from methanol solution. The microscopic and macroscopic nonlinearities of the OH1 crystals are investigated theoretically and experimentally. The OH1 crystals exhibit a large macroscopic nonlinearity with four times larger powder second harmonic generation efficiency than that of analogous CLP crystals containing dimethylamino electron donor. A very high potential of OH1 crystals for broadband THz wave emitters in the full frequency range of 0.1–3 THz by optical rectification of 160 fs pulses has been demonstrated.     

掺铁铌酸钾晶体中的光感生各向异性散射及其光学限制效应

光学限制器是光学系统的保护装置,其保护特性 是由光限制材料与光强或功率有关 的光学非线性效应所产生的,其中光折变晶体中的光感生散射便为该效应之一,多年来受到 世界研究者的广泛研究和关注。对于这类光感生散射,有人提出它是由晶体的表面和体散射 产生的,研究使用的晶体为 LiNbO₃:Fe、LiTaO₃、BaTiO₃,并使用固定的晶体样品和 聚焦透 镜间距。为了进一步探索该散射的产生机理,本文研究了掺铁铌酸钾晶体在激光照射下产生 的光感生各向异性散射特性,利用Z扫描技术测量了该晶体中的 光感生折射率变化,并对晶 体中光散射形成的光学限制特性进行了研究。分析表明该各向异性散射主要是由掺铁铌酸钾 晶体中光感生的柱面透镜效应所导致的。利用光折变晶体中光感生光散射效应的光学限制器 ,一方面可以通过改变晶体尺寸、透镜焦距、小孔光阑大小等来调整其性质,另一方面因其 利用的是低功率连续波激光进行工作,所以能够承受更大的功率和更长的寿命。