孔径光阑限制下高斯光束的传输

对高斯光束在硬边孔径限制下的衍射进行了详细的理论研究,就不同口径的圆孔限制下高斯光束在菲涅耳衍射区和夫琅禾费衍射区的分布进行了理论分析,从而得到了孔径受限高斯光束的横向以及轴向的衍射公式,进而对高斯光束在不同衍射区域内衍射光场分布形状随孔径尺寸变化时的演化规律进行了数值计算,并对小口径光阑受限的高斯光束的衍射与平行光经同尺寸光阑的衍射进行了比较。结果表明在较小口径下,两者的分布基本一致。得到的孔径光阑限制下高斯光束的传输规律为高斯光束在自由空间光通信和光学超分辨中的应用提供了理论基础。     

晶体X射线衍射线形状的理论推导

考虑到不同深度的晶面对X射线吸收的差别,导出了X射线衍射线形状的曲线,获得了精确的衍射曲线形状的表达式,讨论了吸收对衍射峰形状的影响．最后还对理论与实验结果进行了比较．     

量子理论新方法研究光的双缝衍射

用量子理论新方法研究光的双缝衍射实验现象,首先用光的量子理论计算光在缝中双缝衍射的波函数,再由基尔霍夫定律计算光的衍射波函数,由衍射强度正比于衍射波函数模方,从而得到光双缝衍射强度的解析式,把量子理论计算结果和经典电磁理论计算结果以及与实验数据三者进行比较,发现量子理论结果与实验数据符合更好,而经典电磁理论计算结果与实验有一定偏差.从而说明量子理论更能精确解释光的衍射现象.该方法还可进一步研究光的单缝、多缝以及光栅衍射的实验现象.     

Quantum diffraction of wave function in time-domain

The transition of a two-level system driven by a linearly weak chirped pulse is studied. Under the first order perturbation approximation, an analytical expression of the population probability is obtained, which is similar to the one describing Fresnel diffraction by a straight edge. It is shown that the population oscillation results from the diffraction of quantum wave function in time-domain. Supported by the Natural Science Foundation of Shaanxi Province of China (Grant No. 2007A04)     

夫琅和费衍射与大角度衍射

众所周知,夫琅和费衍射的解析强度分布和暗纹位置是在一系列近似情况下导出的。其中最重要的条件是观测点必须限制在傍轴附近,衍射角不能太大,否则得不到简单的解析公式,也就不能称之为夫琅和费衍射。最近发现有人发明错误的理论将夫琅和费衍射概念及其测量扩展到90°角,其结论与常识截然相反,因此,有必要把混淆的概念予以澄清。     

Determination of diffusion profiles in thin film couples by means of x-ray-diffraction

An x-ray method for the determination of concentration profiles in thin film diffusion couples is presented. This method is based on the theory of Fourier analysis of x-ray diffraction profiles which is generalized to polycrystalline samples showing nonuniform lattice parameter. A Fourier synthesis of the concentration spectrum is possible when the influences of the particle size and the strain in the sample as well as the instrumental function are eliminated from the measured diffraction profile. This can be done by means of reference profiles obtained from layers of the diffusion components. Absorption of the radiation in the sample is negligible when diffusion couples of symmetrical sandwich structure are used. The method is tested experimentally in the system Au-Cu.     

基于CCD尺寸测量中图像边缘退化及恢复技术研究

针对直边衍射效应造成的图像边缘退化问题,建立边缘退化模型。从菲涅尔直边衍射理论出发,基于信号与系统理论的图像边缘退化数学描述方法,分析了造成图像边缘退化的原因。通过分析不同光源波长和成像物距下直边衍射强度分布曲线的特点,构造简单函数实现衍射光强分布的近似,进而得到退化系统传递函数;利用退化系统传递函数构造滤波器对获取图像的边缘进行恢复,从而提高尺寸测量精度。实验结果表明:经边缘恢复方法校正后的测量结果误差约为0.02 mm,相对未校正数据的测量结果误差减小0.04 mm,提高了尺寸测量精度。     

单缝衍射图样的计算机仿真与分析

本文通过计算机仿真的方法，给出了在不同接收距离下的单缝衍射图样，并描述了从菲涅尔衍射向夫琅禾费衍射过渡的过程     

圆孔受限波差高斯光束的远场近似及发散度分析

引入复高斯函数对衍射受限的圆孔进行了复高斯分解,得到了波差高斯光束远场衍射的近似解析式。在各种参量条件下,近似解析式所表示的衍射图样与严格的夫琅和费衍射积分的衍射图样完全一致,这表明用此解析式表征远场衍射是正确的。它的形式相对简单,为计算带来极大的方便。基于此,对有波差的高斯光束的远场发散度进行了深入的研究,检验了确定参量的光束随距离的改变而发散度不被改变的特性;同时,探讨了在圆孔限制下,发散度随高斯光束的束腰及波差的改变而变化的关系曲线,结果表明,这两个参量是影响发散度的主要因素。     

表面损伤衍射双向反射分布函数模型建立及分析

建立了包括划痕和坑点在内的表面损伤的衍射双向反射分布函数(BRDF)模型,并分析了模型在各领域中的应用.通过使用非傍轴标量衍射理论,提出了采用相干窗口函数滤波的方法得到非相干光条件下的表面损伤衍射BRDF模型,得到了表面划痕和坑点的散射特性.该方法在表面损伤检测、表面损伤杂光分析以及图像渲染技术等领域都有重要的应用价值...     

Coherent light transmission by a dew pattern

We study both theoretically and experimentally the transmission of coherent light by a drop pattern (dew). The theory is based on the Kirchhoff scalar approach to diffraction. The polarization of the diffracted wave in the zero diffraction order is analyzed separately. The intensity in the zero diffraction order in the far zone is an oscillatory function of the drop size. These oscillations are observed with a pattern of water drops growing on glass. The model allows for the evolution of the important parameters of the drop pattern (average radius and surface coverage) to be obtained from the light intensity in the zero diffraction order.     

Diffraction study of photorefractive hologram under ultrashort pulse readout

Based on the diffraction efficiency equation of Kogelnik, the diffraction effect of a cw photorefractive hologram under ultrashort pulse illumination is theoretically analyzed. We find that the recorded grating has the function of filter to the incident pulse beam. To fully reconstruct the incident pulse, the crystal width must be smaller and grating period must be larger. In this paper we also discuss the total diffraction efficiency of the hologram, and find that the total diffraction efficiency is functions of the crystal length, pulse duration and the grating period. The conclusion of our paper can be used in ultrashort pulse shaping application.     

State space formalism of Feynman diagram theory for acousto-optic interactions:Ⅱ. multifrequency case

A Feynman diagram theory for acousto-optic (AO) interactions is established, which provides a general method to calculate the scattering amplitudes and intensities for both single-frequency and multifrequcncy AO interactions. The method is based on counting the number of allowable Feynman diagrams. The following important assertion has been proved rigorously in this paper. The ratios of the numbers of Feynman diagrams allowable in various B ragg diffractions (isotropie, nondegeneratc birefringent, and degenerate birefringent) to that in Raman-Nath diffraction are independent of the number of different acoustic frequencies, being a function only of the order of the Feynman diagram and the diffraction order of the final state. General expressions for these ratios arc obtained. Based on this, complete perturbation solutions for the scattering amplitudes and intensities are obtained for any kind of AO interactions, any number of acoustic frcquencies, and any final state. This theory gives all results obtain     

多晶材料X射线衍射定量分析的多项式拟合法

提出了多晶材料X射线衍 (XRD)射定量分析的多项式拟合法 ,该方法将数学函数模型与计算机技术相结合 ,在建立衍射峰数学函数模型的基础上 ,利用计算机软件对谱线进行多项式全谱拟合 ,分析实验获得的XRD图谱 ,并求得各衍射峰的积分强度 ,从而精确求出混合试样中各相物质的重量分数。文章主要工作包括 3部分 :1 根据混合物的粉末衍射谱是各组成物相的粉末谱的权重叠加 ,各相的权重因子是与该相在混合物中的体积或重量分数有关的事实 ,建立全谱多项式拟合理论 ,找出各相的权重因子 ,进而求出其重量分数 ;2 数据采集与分析 ,给出了数据的处理方法及步骤 ;3 对定量分析的结果进行了比较讨论。该方法简化了数据处理的过程 ,提高了分析结果的精度 ,使粉末衍射数据处理工作变得相对容易     

编码孔径成像系统中的点扩散函数

在X光编码孔径成像系统中，系统的点扩散函数决定成像系统的成像质量。由于系统的点扩散函数可用来求解系统的传递函数，并可由此制作实现图像重构的滤波器，因此点扩散函数的精确程度直接影响重构过程中图像的质量。本文以标量衍射理论为基础，从理论上推导出了衍射效应条件下编码孔径中圆环的点扩散函数，并将它用于制作光学系统的滤波器。最后利用Wiener滤波函数对编码重叠像的频谱分布进行滤波处理，再经过逆傅里叶变换得到了重构图像。     

二元光学液晶闪耀光栅的特性分析

在二元光学理论的基础上,结合波动光学理论和液晶指向矢的计算提出一种新的二元光学液晶闪耀光栅设计.对液晶光栅电极施加阶梯分布的电压使之形成相位阶梯形分布,推导出液晶闪耀光栅的衍射效率.结果表明,通过改变周期单元光栅电极数日而改变光栅常数,可以改变光衍射角度,一级衍射角度调节范围0°～10°;调节电极电压可以使特定级次衍射光效率达到90%以上,使该级次得到闪耀.     

线性扫频影响超短光脉冲远域衍射场分布的理论分析

本文分析了具有线性扫频高斯型超短光脉冲衍射场的能量分布,教学计算结果显示了线性扫频对衍射场的影响.通过衍射分析可以获得光脉冲的信息.     

近场衍射图样的抽样定理处理方法

提出近场衍射图样的抽样定理处理方法,在近场衍射中,孔径和衍射场分布为或近似为空间有界物,在其频域中可以比较精确地恢复衍射的分布。衍射场频谱带宽的近似值由频谱的幅值大于中心频谱极大幅值的１％的频率范围所确定。     

Strain induced epitaxial relationships of Cr on Co/Pd(111)

The growth and structure of Co ultra-thin films on Pd(111) and Cr on Co/Pd(111) have been analyzed by grazing incidence X-ray diffraction and low energy electron diffraction. It is shown that the in-plane lattice constant of the epitaxial Co film depends on the growth temperature. Although the strain decreases as a function of the Co film thickness, it persists for 20 monolayer (ML) films or even thicker. When Cr is deposited at room temperature on a strained Co film (10 to 20 ML thick) a Kurdjumov–Sachs epitaxial relationship is observed, whereas when Cr is deposited on a Co(0001) single-crystal or on a very thick Co film on Pd(111), a Nishyama–Wassermann orientation is obtained.