锗酸铋晶体二波耦合效应的研究

本文叙述了锗酸铋晶体的生长。采用二波耦合光路测试BGO晶体的衍射效率和增益系数,研究BGO晶体的二波耦合中光波的位相变化。     

非线性光学位相共轭实时补偿大气湍流扰动

利用单色标量光波通过大气湍流的传输理论,在一级玻恩近似下,导出位相共轭波补偿气流扰动的理论,得出在无大气吸收及无限大共轭镜条件下,共轭波可完全补偿大气湍流的结论。实验结果表明,利用受激布里渊散射产生的位相共轭波可得到很好的实时光场恢复。 关键词：     

简并四波混频与位相复共轭(Ⅰ)

光学位相复共轭技术近年来在非线性光学研究的基础上得到迅速发展.这种技术的主要之点,是获得相对于给定光波而言,具有反演位相(或波阵面)的光波.这种技术在数学上相当于一种算符,经它的作用后光波电场的复数表示中的复数空间振幅将转变为其复共轭量,并因此而得名。 光学位相复共轭技术的发展是和光学信息的实时处理相联系的,首先是要设法补偿光波或图象在传播中引起的位相畸变.这样的努力可以追朔到六十年代末和七十年代初.那时,一方面事实上已经提出用实时全息方法产生反向波以补偿位相畸变,另一方面也有不少工作利用瞬态全息图来研究各种…     

简并四波混频与位相复共轭(Ⅱ)

四、简并四波混频的理论研究工作 多年来,围绕简并四波混频的物理机制及影响位相复共轭反射波产生的效率的各种因素,开展了许多理论研究.这里只能作一概要的介绍.1.透明介质的简并四波混频理论 理论分析最初由Yariv等人完成.在图9中,与非线性介质相互作用的有四个波,即抽运光波Ef和Eb,探测光波Ep和共轭反射波Ec.假定它们均近似表示为平面波 一般在实验中探测光波及其共轭反射波相对抽运光波都弱得多,因此可以假定在混频相互作用中抽运光强度不变.现集中研究Ep和Ec的变化.由于四波耦合的结果,产生了波矢分别为Kc及Kp的三阶非线性极化利用…     

再谈尼科耳棱镜中e光的传播

从ｅ光波的波法线分析着手，导出确定ｅ光波的波法线，波射线方向的表达式，论述了ｅ光波在尼科耳棱镜内加拿大树胶层的发生全反射的条件，并给出定量结果。     

相衬显微镜与泽尔尼克

一、相衬显微镜的基本原理及应用1.基本原理 相衬显微技术的关键是把人眼无法直接观察到的位相变化转变为可以直接观察到的强度变化.设位相物体是透明度很高的物体,光波通过该物体后,只改变波的位相,波振幅不变.把该物体放在透镜的物平面上,由于位相物体各部分的光学厚度不同,其复振幅透射系数可写为 f(x,y)=exp[1](1)式中(x,y)为该位相物体的位相分布函数.在透镜的后焦平面(即频谱面)上,f(x,y)的傅里叶变换为(2)式中u=x/λf,υ=y/λf是频谱面上的坐标,也是二维空间函数f(x,y)沿x方向和y方向的空间频率;f为透镜焦距.λ为入射光波K.在应用相…     

软X射线位相型波带片的初步研究

简述了国内外软X射线波带片的发展及其最新研究成果。根据光波的矢量分析方法，数值模拟计算了入射波长为软X射线显微术中常用的2.3、3.2和4.5nm时，以不同材料制作的位相波带片其衍射效率随材料厚度的变化曲线，初步确定出适于制作位相波带片的几种材料。简要介绍了拟采取的制作软X射线位相波带片的方法。     

光纤激光器阵列相干合成中的位相探测与校正方法研究

介绍一高速的位相检测与控制方法，可以对高功率光纤激光器阵列中每一路信号光波的位相进行实时探测与控制，从而使整个系统达到锁相输出的目的.以一路信号光为例，给出该方法的实验研究结果，从中可以看出，闭环控制的结果，可以将该信号光的位相稳定在一设定的静态工作点上. 关键词： 光纤激光器阵列 锁相 外差探测     

光波位相耦合色散效应与固态介质中室温下的光速调控

文章介绍了作者利用光波位相耦合的色散效应调控光速的新机制，并利用光折变位相耦合的色散效应在室温下在Bi12SO20晶体中实现极慢光速和超光速现象．进一步的研究表明，在Bi12SO20晶体中传播的、由位相耦合色散效应引起的慢光和快光由于光折变光强耦合效应而得到了相干放大．     

掺杂铌酸锂晶体位相共轭的温度特性

研究了温度对掺杂铌酸锂晶体位相共轭的影响，实验表明，温度是提高位相共轭波前反射率的一种有铲途径，并用全息光栅理论对此作了解释。     

可压缩混合层光学传输效应理论分析与实验研究

利用量级分析和风洞实验研究了可压缩混合层流动第二发展阶段气动光学效应的规律性.理论分析主要针对二维大尺度结构存在时视线误差(boresight error,BSE)与混合层流场及其特征参数之间的关系进行了讨论.研究结果表明:在混合层发展的第二阶段,时均BSE与对流马赫数呈现出复杂的非线性关系;同时还发现流场中的湍动能和混合层界面处的雷诺应力分布也是影响时均BSE的重要因素;采用细光束穿越混合层流场的风洞试验结果主要证实了时均BSE与对流马赫数之间的非线性关系.     

Mixing by polymers: experimental test of decay regime of mixing

By using high molecular weight fluorescent passive tracers with different diffusion coefficients and by changing the fluid velocity we study the dependence of a characteristic mixing length on the Peclet number, Pe, which controls the mixing efficiency. The mixing length is found to be related to Pe by a power law, L(mix) proportional, variant Pe0.26+/-0.01, and increases faster than expected for an unbounded chaotic flow. The role of the boundaries in the mixing length abnormal growth is clarified. The experimental findings are in good quantitative agreement with recent theoretical predictions.     

四波混频在长距离相干光纤传输中的影响

本文研究光纤非线性现象之一的四波混频对长距离相干多路光纤传输系统的影响.通过对一条长度为550km,采用9个掺铒光纤放大器的频分复用系统的实验,清楚地观察到了四波混频这一光纤非线性.实验的结果符合对四波混频的理论分析与计算.结果表明:对信息容量在每秒10~9bit数量级,采用常规的不归零码作信号方式的多路传输,光纤中的四波混频现象将严重地影响其传输性能.     

Enhanced electron tunneling and Γ–X interlayer intervalley electron transfer in a triple-barrier heterostructure

The enhanced electron tunneling effect and the electron Γ–X intervalley interlayer transfer in the AlAs/GaAs (001) triple-barrier heterostructure have been investigated both experimentally and theoretically. The effects of the external bias on the electronic structure, Γ–X state mixing and higher lying excited energy states are studied. The experimental observations show good agreement with the theoretical predictions based on the scattering theoretical approach of Green's function theory, which can handle electron interlayer intervalley propagation through the layered aperiodic heterostructure under the external bias.     

共振吸收增强的四波混频理论

本文对于共振吸收介质简并四波混频求得了更严格的结果。对(金女)玻璃介质的简并四波混频作用作了具体计算,其计算结果与实验结果基本符合。 关键词：     

不同切型BaTiO3晶体二波耦合特性研究

分析了光折变晶体的电光系数对二波耦合特性的影响,二波耦合能量转移方向不仅依赖于晶体中光生载流子的电荷符号以及入射光与晶体ｃ轴的相对取向,而且依赖于晶体光系数各分量的相对大小;这种特性别明显地表现在相向二波耦合作用中。     

二维拉格朗日坐标系下气粒混合双向耦合对激波流场影响的计算

喷射颗粒与气体混合是内爆压缩领域的热点和难点. 针对喷射混合中的气粒双向耦合问题, 开展了理论建模、离散算法以及颗粒反馈对激波流场的影响研究. 建立了拉格朗日计算框架下的数学模型; 给出了耦合源项的离散算法; 开展了平面及汇聚构型条件下, 气粒双向耦合的数值模拟研究; 发现了颗粒反馈导致气体激波提速现象以及气区流场物理量分布形态的改变, 初步获得了量化分析结果. 本文建立的数学模型、计算方法和获得的新的物理认识, 为深入理解喷射混合现象、解决相关工程应用问题提供了重要理论支撑.     

Additional criteria for MILD coal combustion

We proposed a theoretical basis for Moderate or Intense Low-oxygen Dilution (MILD) coal combustion based on the turbulent scalar energy spectra. This is motivated by the hypothesis that smallest scalar mixing length scales should be on the order of the particle size or smaller to ensure that mixing can occur to prevent formation of diffusion flames. Our proposed criterion is evaluated using several experimental datasets from the literature for coal combustion in both MILD and traditional combustion regimes. The experimental results confirm that the smallest mixing length scales should be of the order of or smaller than the particle diameter, η_mix?d_p, to breakup the heat and mass transfer boundary layers around particles in MILD coal combustion. Results indicate that poor mixing of species with small Schmidt numbers around small particles leads to the high luminous intensity in the reactor. The effects of inlet velocity and jet diameter on the mixing length scales are analyzed. Higher inlet velocity and smaller jet diameter are expected to reach MILD regime. The proposed criterion can be used to guide experimental design to achieve MILD conditions for coal combustion.     

Chaotic mixing in a steady flow in a microchannel

We report experiments on mixing of a passively advected fluorescent dye in a low Reynolds number flow in a microscopic channel. The channel is a chain of repeating segments with a custom designed profile that generates a steady three-dimensional flow with stretching and folding, and chaotic mixing. A few statistical characteristics of mixing in the flow are studied and are all found to agree with theoretical and experimental results for the flows in the Batchelor regime of mixing that are chaotic in time. The proposed microchannel provides fast and efficient mixing and is simple to fabricate.     

Phase matching and focussing effects in noncollinear sum frequency mixing in the near VUV region

We demonstrate that focussing effects are extremely important in determining the bandwidth in sum frequency mixing of ultrashort pulses in the near VUV region. This effect is demonstrated with noncollinear sum frequency mixing performed between the fundamental and the third harmonic subpicosecond pulses of a Ti:sapphire laser. The spectrum of the generated fourth harmonic radiation is significantly broader (by 33%) than the theoretical spectrum obtained if focussing is not taken into account. We have developed a method of calculating the output bandwidth for sum frequency mixing of broadband spectral envelopes whose bandwidths correspond to ultrashort optical pulses, including focussing. The calculated and the measured spectra show excellent agreement.