X,Y,Z切石英晶体Maker条纹理论和实验对比北大核心CSCD

理论上给出了一种计算任意厚度、不同切向石英晶体Maker条纹的方法。通过晶体坐标系和实验室坐标系的对应关系,计算出X,Y,Z三种切向石英晶体的有效二阶非线性系数,从而得到它们的Maker条纹。结果表明X切石英晶体为第一类Maker条纹,而Y切和Z切石英晶体为第二类Maker条纹。实验上使用波长为800 nm的飞秒激光为光源,分别测量了入射角-60°到60°范围内,相同厚度三种切向石英晶体的Maker条纹。实验测量和理论计算的Maker条纹结果基本一致。根据实验测量X,Y,Z切石英晶体Maker条纹的最大值计算出的二阶非线性系数分别为0.3875pm/V、0.2969pm/V、0.2946 pm/V和0.3268pm/V。     

光折变光子晶格中空间二次谐波的产生

用干涉法在自散焦光折变晶体 LiNbO₃：Fe中写入光子晶格的动态过程中，发现了双光束干涉条纹一分为二，四光束干涉点阵一分为四的分裂现象. 研究证明：这是干涉条纹空间频率的倍频现象，是入射的干涉光场与写入的光子晶格之间相互作用的结果. 本实验说明利用光折变效应可以容易地实现干涉光场空间频率的倍频和空间高次谐波的产生，并可利用产生的空间谐波感应出二倍频和高倍频的光折变光子晶格. 关键词： 光折变晶体 光子晶格 空间谐波     

重叠微孪晶界面条纹象的电子显微镜观察与强度计算

观察了面心立方镍基合金中重叠微孪晶界面的各种条纹象,发现它们与α条纹及σ条纹不同,当改变基体或孪晶偏离参量的正负号时,重叠区域条纹的衬度会发生明显的改变,本文将多束动力学衍射理论的叠代法用于重叠孪晶界面几种条纹强度的模拟计算,计算束数包括基体、孪晶及其二次衍射在内共九束,计算的强度曲线与实验强度曲线符合良好,分析结果指出,重叠孪晶界面条纹衬度的明显变化是异常吸收或异常透射效应及基体-孪晶-基体三层晶体多束动力学交互作用的结果。 关键词：     

四波混频实时光学检测

分析了利用掺铁铌酸锂晶体作介质的简并四波混频及其在干涉计量术中应用的原理,描述了被测透明样品的表面各光波及其干涉形成的透射条纹及反射条纹,利用光折变晶体的介电驰豫特性,求得透射条纹和反射条纹的对比度随时间变化的公式及各参数的相互关系。对由透射条纹及反射条纹计算被测透明物体样品折射率和厚度不均匀性的方法作了数学分析,提出一种新型四波混频实时测量透明物体的光学不均匀性的方法和实验光路,对相关参数对测量过程及测量结果的影响作了探讨,得到了平板玻璃样品的干涉条纹图像,计算出实验结果。     

电光材料调制误差对平行光束干涉投影的影响

为研究电光材料调制误差对干涉条纹质量的影响,建立了电光晶体对干涉条纹的成像模型,分析了晶体折射率、平面度与波前调制的关系及其非理想情况下的条纹成像特征。实验表明,晶体折射率的畸变会使干涉条纹变形,折射率离散化阶数直接造成投影条纹的高次谐波成分,甚至使投影条纹严重失真;在折射率线性增长的情况下,晶体平面度在0.1 μm的范围内也会引起干涉条纹畸变。     

Ce:KNSBN晶体中ps激光脉冲二波耦合的直接观察与记录

重复频率为82MHz的ps激光脉冲可在慢响应的光折变晶体Ce:KNSBN中实现二波耦合。本文报道用条纹照相机直接记录的实验结果并给出解释。 关键词：     

迈克耳孙干涉仪测平行玻片折射率实验的进一步研究

用迈克耳孙干涉仪测平行玻片折射率的实验中,干涉条纹的位置和形状出现许多与常规不同的现象。本文对此作一理论分析,并与实验结果相比较。     

晶体双折射测量的干涉条纹重迭法

本文介绍用干涉条纹的重迭与否测量晶体双折射。作者用干涉条纹取代光栅的Ｔａｌｂｏｔ像，主要优点是条纹的对比度好。     

准分子激光辐照HgCdTe半导体材料的损伤机理研究

利用光学显微镜和扫描电子显微镜对248 nm准分子脉冲强激光辐照的HgCdTe晶片表面进行了观察,观察到一些与红外波段内激光辐照HgCdTe晶片时大不相同的实验现象.研究表明,红外波段内1 064nm激光辐照HgCdTe半导体材料的损伤机制主要为光热作用,而紫外波段248 nm准分子激光对HgCdTe材料的损伤机制既包含光化学作用也包含光热作用.分析了准分子激光对晶体的机械破坏现象,同时对HgCdTe材料在激光辐照区的条纹产生机理进行了探讨,发现激光驱动声波理论模型比光学模型和热导波模型能更好地解释HgCdTe晶体表面的条纹现象.     

用晶态半导体做电极的奥氏阈值开关特性

本文描述在Te_(40)As_(35)Ge_7Si_(18)(0.2—1.9μ)薄膜上观察到的非对称阈开关现象。薄膜是在晶体Ge上用快速蒸发淀积的。用热解的石墨接触电极作表面探测时,观察到非对称阈开关现象。用这种方法可以做成“动力学的三稳态”系统。对于n型和p型锗,非对称性恰好相反。适当地加偏压于这种系统,可以用光照来开通。此实验结果和通常用二个石墨电极的阈开关所得结果之间的差别,需要用电子—界面现象来作解释。     

Dynamical Theory of X-Ray Diffraction for Restricted Beams: III. Analysis of Experimental Data for a Porous Crystal

Using the dynamical theory of X-ray diffraction for restricted beams, we have performed quantitative analysis of the structure of an InP(001) porous crystal layer on the basis of experimental data obtained by high-resolution X-ray diffractometry. The parameters of the porous crystal have been determined by simulating coherent and diffuse scattering. The influence of the instrumental function and dynamical effects on the results of investigation has been demonstrated.     

Overcoming of the 12 reflectivity limit in Laue neutron diffraction

Experimental evidence for the overcoming of the 50% peak reflectivity limit in nuetron diffraction in the Laue geometry is presented. Peak reflectivity up to 75%, in spite of the neutron absorption, has been obtained with a bent germanium crystal. This effect has been explained by a simple model based on the dynamical theory of neutron diffraction and appears as a consequence of the elimination, due to a proper curvature, of the Pendellösung effect.     

Dynamical diffraction theory for wave packet propagation in deformed crystals

We develop a theory for the trajectory of an x ray in the presence of a crystal deformation. A set of equations of motion for an x-ray wave packet including the dynamical diffraction is derived, taking into account the Berry phase as a correction to geometrical optics. The trajectory of the wave packet has a shift of the center position due to a crystal deformation. Remarkably, in the vicinity of the Bragg condition, the shift is enhanced by a factor omega/deltaomega (omega: frequency of an x ray, deltaomega: gap frequency induced by the Bragg reflection). Comparison with the conventional dynamical diffraction theory is also made.     

Aperture (slit) effects on the dynamical diffraction of X-rays and thermal neutrons

With increasing accuracy of perfect crystal methods, the effects of apertures (slits) on angular and spacial intensity distributions in dynamical perfect crystal diffraction have become quite important. We present an analytical treatment of such effects. The results are first applied to the diffraction of rays delivered by a source of given lateral extension, i.e. where the critical size of the source as such is essentially influencing the dynamical diffraction phenomena. Both the Laue and the Bragg geometry are considered. Next we calculate the change which a rocking curve measured in either geometry suffers from a slit with varying width and position in front of or between the crystals. Finally we report a pertinent experiment which we have performed in the Laue geometry. We find good agreement with the calculations. It follows that whenever dynamical diffraction is used in quantitative measurement the possible influence of diffraction from diaphragms requires special attention and analysis. For the latter the theory presented here is very well suited.     

A study of the contrast on growth striations in silicon by X-ray double crystal topography in the Laue case

The image of growth striations in Si formed by the double crystal X-ray topography in the Laue case (DCTL) is investigated. The results of the dynamical diffraction theory for crystals with small microdefects have been compared with the contrast behaviour determined experimentally. It has been found that the theory explains qualitatively the contrast on the striations and it has been demonstrated that the DCTL method is suitable for detection of the presence of small microdefects in growth striations. Since the paper completes a series of papers on X-ray topography of growth striations, some general conclusions are formulated concerning the applicability of the X-ray topographical methods to the investigation of the structure of the growth striations     

Diffraction effects in low-energy electron emission

The origin of diffraction peaks in the energy distribution of intensity of low-energy (< 1000 eV) electron emission from crystals is discussed from the standpoint of the dynamical theory of diffraction. The emitted electrons are considered to originate at relatively incoherent point sources in the crystal. The two-beam approximation of dynamical theory is used. The theory accounts for the chief regularities of diffraction peaks: temperature-dependence of peak intensities like that for low-energy electron diffraction (LEED) peaks, correlation of peak energies with X-ray absorption fine structure, and correlation of peak energies with the energies of normal-incidence LEED peaks in specular reflection. It is shown that the conditions for diffraction peaks coincide with the conditions for emergence of Kikuchi lines. It is predicted that for energies just above those of diffraction peaks, such emergences should be observable in the angular distribution of emission as intensity minima for emission along low-index crystal axes. Theory of Kikuchi band profiles is developed in an Appendix.     

A fresh look at diffraction from a nonabsorbing perfect crystal in the Bragg-Laue configuration

The Bragg diffraction from a thick, nonabsorbing perfect crystal theory of dynamical diffraction. The intensities of two beams, one in the incident and the other in the diffracted direction, exciting the side face of the crystal are characterised. The implications of such beams for neutron diffraction experiments are indicated.     

Dynamische Theorie der Röntgenbeugung für deformierte Kristalle

A dynamical theory of X-ray diffraction is formulated, which is not only applicable to ideal but also to deformed crystals. Wavefields are considered which are not in dynamical equilibrium and hence possess space variable amplitudes; in deformed lattices the wave-vectors too are weakly variable. For the amplitudes, generalized dynamical equations are derived which form a set of hyperbolic differential equations of first order. They differ fromEwald-Laue's equations by a term expressing the deviation from equlibrium; in addition the coefficients vary as components of the deformation tensor. The equations allow a direct transition from the usual dynamical theory in the ideal crystal to the kinematical approach. In the two-beam case a differential equation for the amplitude ratio is given. For very weak distortions the general equations contain as a special case the “method of modified Blochwaves”. The deformation limits where the methods apply have been pointed out.     

透射式GaAs光电阴极的X射线衍射研究

本文介绍了高精度多晶多反射X射线衍射仪的一种新的应用.首次将其应用于研究高灵敏度第三代微光象增强器中由掺Zn的p型GaAs/GaAlAs、玻璃组成的光电阴极的材料特性；发展了用倒格子空间衍射图方法评价光电阴级组件晶体质量的方法.通过分析得知,衍射强度在倒格子空间沿。方向展宽主要起因于晶体中的嵌镶效应的增强.文中采用衍射动力学理论的计算方法并忽略初始条件,模拟后得到的曲线与衍射强度沿ω/θ方向的投影强度曲线符合的比较好.粘接良好的阴极样品表明,GaAs/GaAlAs晶格常数的变化基本上可以消除,但粘接引起的嵌镶效应的增强却不能完全消除.