平面透射光栅的菲涅耳衍射

从标量场的菲涅耳衍射理论出发,研究了球面波入射平面透射光栅的衍射场,导出菲涅耳衍射场的复振幅分布,并得到光栅菲涅耳衍射角的计算公式．结果表明,在理想情况下菲涅耳衍射的每一级衍射波都是一个球面波;在对菲涅耳衍射角进行新的定义后,衍射角的计算仍然可以采用夫琅禾费衍射的光栅方程．     

Phase diffraction gratings based on a Si(400) crystal

The X-ray optical properties of diffraction gratings fabricated on the basis of a Si(400) crystal with a period of D = 1 μm are studied by triple-crystal X-ray diffractometry. The diffraction gratings are manufactured both by silicon profiling during the process of plasma chemical etching and by forming a phase-shift grating on the surface of a Si crystal. The principal difference in the diffraction properties of these gratings is demonstrated. The presence of an Au phase-shift grating is shown to lead to the formation of a two-dimensional diffraction pattern, whereas Si profiling leads to the formation of only a one-dimensional diffraction pattern.     

Angular spectrum analysis of near-field diffraction of a small aperture

The near-field diffraction of a nanometer aperture is studied in this paper according to the angular spectrum theory. The mathematic expressions of the near-field diffraction are presented, and the influences of the polarization of the electromagnetic field and the evanescent wave on the diffraction in near field are analyzed by means of vector and scalar diffraction theory, respectively. The transverse and longitudinal diffraction intensity distributions of a small aperture are numerically calculated, and the results show the near-field diffraction of a small aperture is influenced strongly by the vector property of the electromagnetic field and the evanescent component.     

圆孔“衍射波”的相位特性

在标量衍射理论的基础上,导出了圆孔衍射的“边界衍射波”的级数表达式,提出圆孔衍射产生的“衍射波”概念,对“边界波”和“衍射波”的相位特性作了讨论和比较.     

Diffraction of a two-shock configuration by a convex cylindrical surface

The subject of this work is numerical investigation into the diffraction of a shock-wave configuration by a convex cylindrical surface. The diffraction is a stage of interaction of a shock wave with a two-dimensional body. It is preceded by the stage of shock wave reflection from the front surface of the body, the back surface of which has a convex cylindrical shape. The two-or three-shock configuration formed on the front surface diffracts by the back cylindrical surface. The emphasis is on studying the diffraction of the two-shock wave configuration with the diffraction angle varying continuously. The object under study a wedge with an inclined front surface and convex cylindrical back surface. The results of numerical investigation are obtained by integrating the Euler equations. Flow features associated with the simultaneous diffraction of the incident and reflected shock waves are revealed. The evolution of the gasdynamic system (stagnation wave + TU layer) arising inside the diffraction area is studied. Breakaway and vorticity initiation are considered. It is shown that the positions of the line of separation and TU layer change in the course of diffraction. They merge together at the stage of steady flow. Comparison is made between the flow formed upon diffraction of the two-shock configuration by the cylindrical surface and the flow generated upon diffraction by horizontal and vertical surfaces.     

关于由衍射片的背面反射光形成的衍射图样的讨论

在光的衍射实验中,我们看到的一般是由通过衍射片的直射光形成的衍射图样,但在衍射片的另一面,同样存在着另一个衍射图样,它是由衍射片的背面反射光形成的,两个衍射图样关于衍射片对称.本文给出了这种实验现象,并用巴比涅原理解释了这种现象.     

水基磁性液体的场诱导光衍射特性的研究

设计了一套用于研究磁性液体的场诱导静态和动态光衍射特性的实验装置.通过在样品的后方放置一个适当孔径的光阑,实现了定量研究其衍射特性的目的.采用沿衍射方向移动光阑的方法定量地研究了衍射光的空间分布.设计了一个指数衰减函数用来拟合动态衍射实验的数据,获得动态衍射的特征时间.以两种不同浓度的表面包覆型水基氧化铁磁性液体样品为例,定量地实验研究了其场诱导光衍射特性与外磁场强度和样品浓度的关系.结果表明,磁性液体的场诱导结构对光的静态和动态衍射与外磁场的强度和磁性液体的浓度有关.其静态衍射与外磁场强度呈非单调的关系;其动态衍射的特征时间与外磁场的强度成反比,与磁性液体的浓度成正比.对实验中观察到的场诱导静态和动态衍射特性的物理机理进行了详细的分析.     

水基磁性液体的场诱导光衍射特性的研究

设计了一套用于研究磁性液体的场诱导静态和动态光衍射特性的实验装置.通过在样品的后方放置一个适当孔径的光阑,实现了定量研究其衍射特性的目的.采用沿衍射方向移动光阑的方法定量地研究了衍射光的空间分布.设计了一个指数衰减函数用来拟合动态衍射实验的数据,获得动态衍射的特征时间.以两种不同浓度的表面包覆型水基氧化铁磁性液体样品为例,定量地实验研究了其场诱导光衍射特性与外磁场强度和样品浓度的关系.结果表明,磁性液体的场诱导结构对光的静态和动态衍射与外磁场的强度和磁性液体的浓度有关.其静态衍射与外磁场强度呈非单调的关系|其动态衍射的特征时间与外磁场的强度成反比,与磁性液体的浓度成正比.对实验中观察到的场诱导静态和动态衍射特性的物理机理进行了详细的分析.     

光栅周期包含的Bragg层数对Bragg型凹面衍射光栅的影响

单个衍射光栅周期所包含的Bragg周期层数是连续Bragg齿型凹面衍射光栅的主要参数之一,该参数可改变光栅齿结构,对凹面衍射光栅的分辨力.自由光谱范围及衍射效率有重要影响.本文通过理论分析与仿真模拟,对比了4种不同层数的Bragg型凹面衍射光栅的特性参数.研究结果表明:在衍射光栅尺寸不变的情况下,改变单个光栅周期包含的Bragg周期层数不会显著提高器件主衍射级次的分辨力;单个光栅周期包含的Bragg周期层数与光栅可衍射的级次数成正相关.单周期层数的Bragg凹面衍射光栅的主衍射级次效率最高,其可衍射的级次数最少,且其他衍射级次分散的能量最少;增加单个光栅周期所包含的Bragg周期层数会降低主衍射级次的自由光谱范围.该研究对于设计低插损、高分辨率、宽工作波段的波分复用器或光栅光谱仪具有重要的指导意义.     

高功率激光装置的线性传输特性

在菲涅耳数的基础上重新定义了衍射特征量,并将其定义扩展至聚焦或发散光路,定义了一个光学系统中各光学元件衍射特征量的符号。通过全新的定义和扩展,研究了波前畸变对近场调制度的影响以及正弦调频光谱色散平滑光束衍射传输引入的幅频调制的大小。以神光-Ⅲ主机主放大级为例,研究了元件波前畸变对近场调制度的影响以及正弦调频光谱色散平滑光束衍射传输引入的幅频调制的大小。衍射特征量与能流分布F相结合,可以作为评价高功率激光装置线性传输效应的一项受限指标,指导高功率激光装置的设计。     

Diffraction effects on bulk-wave ultrasonic velocity and attenuation measurements

The loss and phase advance due to diffraction are experimentally observed by measuring the amplitude and phase of radio frequency (rf) tone burst signals in the VHF range, in an ultrasonic transmission line consisting of a buffer rod with an ultrasonic transducer on one end, a couplant of water, and a solid specimen of synthetic silica glass. The measured results agree well with the calculated results from the exact integral expression of diffraction. The diffraction effects on the velocity and attenuation measured in this frequency range and their corrections are investigated to realize more accurate measurements. It is shown that attenuation measurements are influenced by diffraction losses and can be corrected by numerical calculations, and that velocity measurements are affected by the phase advance caused by diffraction. This investigation demonstrates that, in complex-mode velocity measurements, in which the velocity is determined from the measured phase of the signals, the true velocity at each frequency can be obtained by correction using the numerical calculation of diffraction. Based on this result, a new correction method in amplitude-mode velocity measurements is also proposed. In this new method, the velocity is determined from the intervals of interference output obtained by sweeping the ultrasonic frequency for the superposed signals generated by the double-pulse method. Velocity may be measured accurately at frequencies in the Fresnel region, and diffraction correction is essential to obtain highly accurate values with five significant figures or more.     

一维丝室气体探测器衍射像差的修正方法研究

一维位置灵敏单丝气体探测器采用单根镀金钨丝和200根阴极感应条的探测结构, X射线在阳极丝上产生的信号被多个阴极条感应, 利用重心法得到X射线的原初电离点的位置信息, 位置分辨率达到160 μm(半高全宽). 在同步辐射衍射实验中, X射线通过样品后会形成不同大小的衍射环, 本实验中测量得到11.148°和14.201°的两组衍射角位置信息; 通过平行移动一维探测器在衍射环范围内多次扫描, 可以重建得到二维衍射环. 由于一维探测器的气体厚度和入射窗宽度会给测量结果带来像差, 分析发现像差的影响大于一维探测器的位置分辨. 基于相应的物理分析对测量到的衍射位置进行修正, 修正后的衍射位置相比修正前的衍射位置的相对像差最大改善达到7%, 该方法实现了无像差二维衍射环的重建.     

Diffraction from a moving grating

A first-principles tutorial account is given for the diffraction of either light or free, non-relativistic, massive particles from a moving grating. Discussion on the properties of the moving grating including non-reciprocity is followed by considering both Raman-Nath (thin grating) diffraction and Bragg (thick grating) diffraction in either transmission or reflection geometry. Use of four-momentum conservation with dispersion relations yield the angles of diffraction. The increase in the angle of diffraction for grazing incident by using a moving grating relative to using a static grating is calculated. It is shown that this increase is possible only for Raman-Nath geometry.     

Atomic structures by direct transform of diffraction patterns

We propose all the diffraction patterns can be directly transformed to provide three-dimensional atomic structures for the system studied. Depending on the scattering process, either the holography or Patterson transform scheme is used. For diffraction patterns which are generated from a localized emitter source or dominated by an inelastic-scattering feature like core-level photoelectron or low-energy Kikuchi electron, holography transform is needed. On the other hand, for diffraction patterns which were dominated by elastic-scattering, like grazing-incidence X-ray diffraction, electron correlated thermal diffuse scattering or low-energy electron diffraction curves, Patterson transform is needed. To prove our point, high-fidelity and artifact-free three-dimensional atomic structures obtained by transform of low-energy Kikuchi electron patterns and low-energy electron diffraction curves are presented. The future of these direct methods by transforming diffraction patterns will be discussed.     

Surface studies by electron diffraction

The problems in the analysis of surface structures by means of electron diffraction, particularly at low energy, are reviewed. A brief introduction is given to the basic scattering and diffraction phenomena occurring at a solid surface after which the nature of the experimental diffraction data is described. The theoretical interpretation of the diffracted intensity by various kinematical and dynamical methods is outlined and the present difficulties in obtaining a complete surface structure determination are examined. The different types of ordered and disordered layers which may be formed on a surface—usually by adsorption of foreign species—are discussed and the interpretation of the corresponding diffraction patterns is illustrated by some examples.     

Light diffraction features in an ordered monolayer of spheres

The structure and optical diffraction properties of monolayers of monodisperse spheres crystallized on transparent dielectric substrates are studied. Two types of diffraction phenomena are considered: surface light diffraction on the lattice of spheres and waveguide resonances in the monolayer plane. For experimental study of these phenomena, optical retroreflection and transmission spectra are measured as functions of the light incidence angle and azimuthal orientation of the incidence plane. The monolayer structures determined by scanning electron microscopy and light diffraction methods are in quantitative agreement. It is concluded that one-dimensional Fraunhofer diffraction is applicable to describe surface diffraction in the hexagonal lattice of spheres. In the case of oblique light incidence, anisotropy of diffraction and transmission spectra depending on the light incidence plane orientation with respect to the sphere lattice and linear polarization of incident light is detected. Waveguide resonances of the planar two-dimensional photonic crystal are approximated within the light diffraction model in the “empty” hexagonal lattice. The best approximation of the waveguide resonance dispersion is achieved using the effective refractive index, depending on the wavelength. Surface diffraction suppression by waveguide resonances of the photonic crystal is demonstrated. Surface diffraction orders are identified as diffraction at singular points of the Brillouin zone of the planar twodimensional photonic crystal.     

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.     

对实屏的夫琅禾费衍射中心亮点(亮纹)的半定性半定量论证

光经圆盘、细丝等实屏衍射后,衍射光场中其几何阴影中心有不为零的光强分布.显然这是阐述光的波动性的最好例证,它比圆孔、单缝之类的光孔衍射更具说服力.然而对圆盘等的衍射中心亮点(如泊松点)的论证通常都是从菲涅耳衍射出发,但是在绝大多数非物理类专业的大学物理中,对光的衍射的具体分析都只涉及夫琅禾费衍射,因而给学生对于上述问题...     

Exact diffraction calculation from fields specified over arbitrary curved surfaces

Calculation of the scalar diffraction field over the entire space from a given field over a surface is an important problem in computer generated holography. A straightforward approach to compute the diffraction field from field samples given on a surface is to superpose the emanated fields from each such sample. In this approach, possible mutual interactions between the fields at these samples are omitted and the calculated field may be significantly in error. In the proposed diffraction calculation algorithm, mutual interactions are taken into consideration, and thus the exact diffraction field can be calculated. The algorithm is based on posing the problem as the inverse of a problem whose formulation is straightforward. The problem is then solved by a signal decomposition approach. The computational cost of the proposed method is high, but it yields the exact scalar diffraction field over the entire space from the data on a surface.     

实验研究探测器大小与散焦长度对无透镜鬼衍射的影响

无透镜鬼衍射是一种特殊的非局域关联成像技术,通过对包含物体信息的测试光路和不含物体信息的参考光路的光场强度涨落关联进行测量,在参考光路上可得到物体的衍射图样。利用赝热光源实验研究了探测器尺寸大小和光路散焦长度对无透镜鬼衍射质量的影响。实验以四缝物体为例,定量研究了探测器大小和散焦是如何改变无透镜鬼衍射的成像结果,并和理论模拟进行了比较,获得了比较一致的结果。利用图像相关度定量分析了实验结果与理想无透镜鬼衍射图像的差别,发现这两者都会使无透镜鬼衍射的质量变差。