高精度激光衍射测径系统

本文介绍采用线阵CCD的激光衍射测径系统.该系统中CCD视频信号被逐位进行模/数转换,变为相应的数字量.利用最小二乘法对衍射图样进行局部曲线拟合,确定暗纹间距S.因而,衍射测径的精度不再受CCD象元中心距大小的限制.     

基于小波分析粘胶长丝测径系统数据处理研究

本文提出一种利用小波平滑去噪，改善粘胶长丝衍射图像处理精度的方法。采用可调焦镜头和面阵CCD构成的摄像系统，拍摄粘胶长丝衍射图样。选择恰当的小波分析函数，对衍射图样轴线上的灰度数据实现消噪及平滑处理，结合曲线拟合技术，确定衍射暗条纹的中心位置，提高了中心定位精度。基于该方法设计出粘胶长丝直径检测系统，测量精度达到0．2μm。     

消旋检测系统像差校正衍射元件的加工分析

基于一种检测机载制冷型CCD消旋机构的红外光学系统,对非球面为基面的衍射元件进行系统像差校正。通过控制衍射元件非球面基面的方法得到衍射面面型,使用金刚石单点车削技术(SPDT)进行衍射元件的高精度加工,并对影响衍射元件加工精度及加工工艺因素进行了分析。     

一种新型测量旋光色散的方法

提出了一种新的测量旋光色散的方法。该方法利用白光LED作为光源,经起偏棱镜、样品管和检偏棱镜后,复色偏振光经平面衍射光栅分光后,由线阵CCD进行采集,CCD的每个像元对应接收复色偏振光经分光后的某一波长的光信号,在检偏器旋转一周内,获得相应的光强数据,使用拟合算法,对每一个像元所采集的光强数据逐一进行处理,最终得出CCD像元所对应波长的旋光度,最后得到旋光色散数据。并利用标准石英管进行了实验研究,证明了这种测量方法的可行性。     

激光全场光衍射测量

提出了测量全场应力应变的一种新方法。它可用于测量被测物体整个表面的变形量。这种方法为非接触测量,不影响被测量物的表面。其方法是利用全场激光衍射通过CCD采集计算机成像。编写数字图像处理程序对被测物表面变形信号进行处理取得被测物表面的全场变形信息数据,同时可以观察衍射条纹形貌以及变化全过程。     

基于小孔夫琅和费衍射法的CCD光电响应特性标定研究

对CCD的光电响应特性进行标定,是保障CCD测量系统测量精度和系统可靠性的关键技术环节,对系统测量结果有着直接的影响。对现有的各种CCD光电响应特性标定方法进行对比分析后,引入小孔夫琅和费衍射的方法。推导了该法中Airy斑的理论相对光强分布I/I0与CCD像素位置n之间的定量关系,完成了对特定面阵CCD光电响应特性标定实验。在数据处理过程中采用二次曲线拟合法准确获得了灰度曲线的峰值位置,实现了Airy斑归一化理论光强分布曲线与CCD实测灰度分布曲线对准,解决了这种方法的中心对准问题。最终的标定结果经误差分析满足要求。     

使用CCD进行动态高精度角度测量

本文讨论了使用线阵CCD作为光电接收器的高精度动态测角系统的原理,结构及系统的精度,最后对衍射及滤波对测量精度的影响也进行了分析。     

小孔夫琅和费衍射法标定CCD光电响应特性

对比分析现有的各种CCD光电响应特性标定方法后,引入了利用小孔夫琅和费衍射标定CCD光电响应的方法.推导了该方法中Airy斑的理论相对光强分布I/I0与CCD像素位置n之间的定量关系,完成了对特定面阵CCD光电响应特性标定实验.在数据处理过程中,采用二次曲线拟合法准确获得了灰度曲线的峰值位置,实现了Airy斑归-化理论光强分布曲线与CCD实测灰度分布曲线对准,解决了这种方法的中心对准问题,得到准确的灰度峰值位置n0为404.650 0,获得了特定的CCD光电转换特性曲线.标定结果表明,平均相对误差为0.77%,拟合结果可靠.     

基于高斯拟合测量CCD灵敏度均匀性

在精密度要求较高的图像测量领域中,CCD灵敏度的不均匀对测量精度有较大的影响。因此,提出了一种基于小孔衍射原理的高斯曲面拟合像面光场测量CCD灵敏度均匀性的方法。由于CCD自身的物理结构设计不均匀性、响应非线性以及暗电流等噪声因素使得光响应偏离实际值,该方法通过对CCD像面上感兴趣光场域进行高斯曲面拟合来确定零点像素的灰度响应。对所有像素测量完成之后通过归一化即可计算出CCD灵敏度均匀性。实验结果表明:对所使用的CCD47-10系列,计算其CCD灵敏度均匀性为2.14%。该测量方法基本满足设计原理简单、稳定性可靠、抗干扰能力强的要求,完成了快速、自动测量。     

CCD检测衍射条纹的数据处理

分析了中值滤波法和集平均法的局限性，给出了单缝衍射条纹的“特征谱线”，提出特征谱线滤波法，该法可以满意地滤去CCD检测衍射条纹数据的波纹。     

Optimization of resolution by FDTD analysis in aligner lithography

A mask aligner can transcribe a pattern from a photomask to an exposure substrate by Fresnel diffraction. A diffraction fringe, specific to Fresnel diffraction, appears on a light intensity distribution of the pattern (a diffraction pattern image), and the formation of the pseudo-pattern restricts the resolution performance. The diffraction fringe can be smoothened by expanding the spread of the illumination source, and thus, the pseudo diffraction can be attenuated. However, this also causes a change in light intensity at the pattern edge to be attenuated, and the error of pattern line width to process change becomes large. Since edge diffraction patterns can be calculated by finite difference time domain (FDTD) analysis, the size of light source providing optimum resolution can be predicted by calculating and comparing pattern images corresponding to the size of the light source using this analysis. Therefore, by introducing an illumination optical system that can arbitrarily set the size of a light source to a predicted value, optimum resolution can be obtained without prior trial exposure. This study shows that the resolution of an aligner can be optimized by prior prediction, by introducing a multiple smoothing optical system that has been developed as an illumination system. This system realizes uniform illumination distribution on both a pupil plane and photomask plane and has an adjustable aperture mechanism that, by combining it with FDTD analysis, can arbitrarily set the size of the light source.     

JECP/PCED--a computer program for simulation of polycrystalline electron diffraction pattern and phase identification

A computer program for simulation of polycrystalline electron diffraction pattern and phase identification is described. In addition to simulating electron diffraction pattern for a single phase, the program has the ability to model two phases with selected mass ratio. Experimental polycrystalline electron diffraction patterns can be directly compared to simulated patterns for phase identification. Examples of how to use the program are also given.     

Quantitative evaluation of high-resolution features in images of negatively stained Tobacco Mosaic Virus

This study investigates the causes of the apparent differences between the optical diffraction pattern of a micrograph of a Tobacco Mosaic Virus (TMV) particle, the optical diffraction pattern of a ten-fold photographically averaged image, and the computed diffraction pattern of the original micrograph. Peak intensities along the layer lines in the transform of the averaged image appear to be quite unlike those in the diffraction pattern of the original micrograph, and the diffraction intensities for the averaged image extend to unexpectedly high resolution. A carefully controlled, quantitative comparison reveals, however, that the optical diffraction pattern of the original micrograph and that of the ten-fold averaged image are essentially equivalent. Using computer-based image processing, we discovered that the peak intensities on the 6th layer line have values very similar in magnitude to the neighboring noise, in contrast to what was expected from the optical diffraction pattern of the original micrograph. This discrepancy was resolved by recording a series of optical diffraction patterns when the original micrograph was immersed in oil. These patterns revealed the presence of a substantial phase grating effect, which exaggerated the peak intensities on the 6th layer line, causing an erroneous impression that the high resolution features possessed a good signal-to-noise ratio. This study thus reveals some pitfalls and misleading results that can be encountered when using optical diffraction patterns to evaluate image quality.     

The possibilities for electron diffraction in biology

The techniques whereby an electron microscope may be used to observe the low angle electron diffraction pattern from crystallized macromolecules are described. A discussion is then presented of the advantages and disadvantages of the technique relative to X-ray diffraction, high resolution electron microscopy and optical diffraction or computer analysis of electron micrographs.     

Advances in TEM orientation microscopy by combination of dark-field conical scanning and improved image matching

A new approach to automatic TEM‐based orientation microscopy is presented, which is based on a combination of the techniques of dark-field conical scanning and improved image matching, and a diffraction pattern simulation method. For indexing, a full experimental diffraction pattern is compared to all possible pre-calculated diffraction patterns for the given structure by image matching. In order to speed up this relatively calculation-intensive algorithm, polar transformation and, most important, circular projection that increase the speed of pattern indexing by a factor of about 50 are proposed. A microstructure of submicron scale and crystallographic orientations in nanocrystalline materials are measured successfully. It is proposed that the taken approach of dark-field conical scanning and improved image matching may be, in principle, better suited for TEM-based orientation microscopy than serial orientation mapping.     

Three-dimensional dynamic morphometry on a diffraction pattern in the focal plane

A new type of morphometry, which shortens the scanning time of precise observation by confocal microscopy, has been investigated. To analyse the 3-D distribution of active sites on a living cell, microspheres of the same size were immunologically marked on specific sites on a cell. Incident coherent light was scattered on the microspheres and the scattered light from each microsphere superimposed upon each other giving a diffraction pattern of the examined cell. Several series of interference fringes were generated on the diffraction pattern, according to the phase difference of the microspheres. These interference fringes on the 2-D diffraction pattern enable the (relative) 3-D positions of the microspheres to be determined. 3-D dynamic morphometry on a 2-D diffraction pattern with interference fringes speeds up imaging in confocal microscopy.     

Geometric analysis of surface resonance conditions in reflection high energy electron diffraction

A three-dimensional analysis in reciprocal space is used to analyse reflection high energy electron diffraction (RHEED) patterns. Particular emphasis is placed on investigating the surface resonance phenomenon, the resonance conditions, and the diffraction mechanisms. The surface resonance regions defined by the resonance beam threshold conditions are related to the limits for the specular reflection spot in the diffraction pattern. The introduction of an Ewald sphere of varying radius is shown to be useful in understanding the surface phenomenon. Simulations based on the geometric theory, taking account of the surface refraction effect, describe very well the RHEED pattern geometry from the (111) surface of a platinum single crystal.     

Beyond the crystallization paradigm: structure determination from diffraction patterns from ensembles of randomly oriented particles

We amplify on the principles of the method we have recently proposed for recovering an oversampled diffraction pattern of a single particle from measured diffraction patterns from multiple particles in orientations related by rotation about an axis parallel to the incident radiation. We propose an alternative method of phasing a reference resolution ring by means of a non-negativity constraint on the diffraction intensities, point out the need for caution about enantiomeric ambiguities in the reconstruction of a diffraction pattern from its angular correlations, and show that converged correlations may be deduced by appropriate averaging of even very noisy data.     

Towards automated diffraction tomography: part I--data acquisition

The ultimate aim of electron diffraction data collection for structure analysis is to sample the reciprocal space as accurately as possible to obtain a high-quality data set for crystal structure determination. Besides a more precise lattice parameter determination, fine sampling is expected to deliver superior data on reflection intensities, which is crucial for subsequent structure analysis. Traditionally, three-dimensional (3D) diffraction data are collected by manually tilting a crystal around a selected crystallographic axis and recording a set of diffraction patterns (a tilt series) at various crystallographic zones. In a second step, diffraction data from these zones are combined into a 3D data set and analyzed to yield the desired structure information. Data collection can also be performed automatically, with the recent advances in tomography acquisition providing a suitable basis. An experimental software module has been developed for the Tecnai microscope for such an automated diffraction pattern collection while tilting around the goniometer axis. The module combines STEM imaging with diffraction pattern acquisition in nanodiffraction mode. It allows automated recording of diffraction tilt series from nanoparticles with a size down to 5nm.