用数字全息术检测轮胎气泡缺陷

提出了一种基于二次曝光数字全息干涉术的子午线轮胎内部气泡缺陷无损检测方法.该方法利用数字全息记录系统记录下轮胎初始状态和受热膨胀变形状态的数字全息图,在计算机中对这些数字全息图分别再现后,将代表轮胎变形状态的再现波前与其初始状态的再现波前进行干涉,获得携带轮胎变化信息的干涉条纹和相位分布;分析了存在气泡缺陷区域的轮胎和无缺陷轮胎两种情况下的干涉条纹及其相位分布的特点和区别.分析结果表明:在轮胎内部存在缺陷的位置,其二次曝光数字全息干涉条纹具有与质量正常位置处干涉条纹相对独立的特征,该方法可以检测出轮胎气泡缺陷,记录系统的横向分辨率为16.4 μm.     

基于二次曝光数字全息技术的轮胎内部气泡缺陷检测方法研究

提出一种基于二次曝光数字全息干涉计量术的轮胎内部气泡缺陷无损检测方法。该方法利用数字全息记录系统记录下轮胎初始状态和受热膨胀变形状态的数字全息图,在计算机中对这些数字全息图分别再现后,将代表轮胎变形状态的再现波前与其初始状态的再现波前进行干涉,获得携带轮胎变化信息的干涉条纹和相位分布,分析存在气泡缺陷区域的轮胎和无缺陷轮胎两种情况下的干涉条纹及其相位分布的特点和区别。研究结果表明：在轮胎内部存在缺陷的位置,其二次曝光数字全息干涉条纹具有与质量正常位置处干涉条纹相对独立的特征,该方法可以检测出轮胎气泡缺陷。     

全息光弹性中的非漫射照明全息摄影

在全息光弹性试验中,采用非漫射照明全息摄影所获得的全息图,可在白光下再现。所需的光弹性数据,可直接取自全息图。此外,全息图再现时的等和线,不随观察视线的改变而漂移,干涉条纹细而清晰。     

无透镜全息显微细胞成像

为了同时满足较大的视场和较高分辨率的需求,开发了一套全息无透镜显微成像系统和配套算法,实现对微米级样品的无透镜显微成像。搭建了一套由LED光源、针孔、被测样品与CMOS图像传感器组成的全息无透镜显微成像系统,并对针孔直径、成像面尺寸、光源到样品的距离,以及样品面到CMOS图像传感器的距离进行了优化。其次,开发了从系统采集的全息图中恢复样品图像的角谱法算法。最后,使用该成像系统和配套算法,分别对具有微米级结构分辨率测试靶,和肺癌细胞悬浮液进行了显微成像。该全息无透镜显微成像系统的分辨率为4.4μm,成像视场尺寸为5.7 mm×4.3 mm,实现了微米级结构和肺癌细胞较清晰的显微成像。全息无透镜显微成像系统结构简单、无像差干扰,可以实现大视场下较高分辨率的显微成像。     

减少液晶显示全息图的再现误差

提出计算机生成全息图的新的算法.全息条纹数据以计算机图像格式存储,并以视频信号传输到液晶板上显示,用该电全息实时三维成像.液晶板的分辨率、对比度及由全息图的灰度决定的调制度会对再现造成影响.因此在算法中考虑这些因素,并通过确定像面分布的情况下逆推求出全息面上的光波的振幅和位相分布再优化编码来减少再现误差.最后给出了实验结果,并对再现进行像质评价.     

新型数字波面斐索干涉仪的设计

介绍结构简单的激光斐索干涉仪设计原理及方法,该仪器以其设计思想新颖、单幅图像实时处理、计算机对干涉条纹处理并实时显示计算结果、数字显示被测光学零件的面形信息,相对于传统测量方法具有无以伦比的优势.同时简单介绍对干涉条纹的处理思路,将实用的图像处理算法如图像滤波、二值化、细化等方法用于采集到的干涉条纹处理,为后续准确确定条纹位置、条纹间距、条纹变形作前期准备工作.     

一种大视野超分辨结构光照明显微成像方法

近年来结构光照明显微术(SIM)在技术发展和应用方面都受到了广泛关注。然而,传统采用空间光调制器(SLM)进行条纹投影的SIM成像视野有限。为满足生物医学研究中高通量显微成像的需求,本文基于SIM开发一种基于激光干涉的大视野超分辨荧光显微成像系统。将用于投射条纹图案的2D光栅和用于控制条纹方向相移的SLM相结合,突破数字投影设备对条纹数量和精细度的限制。开发一种空域重建超分辨图像的算法来提高成像速度。最后,搭建1套结构光照明荧光显微成像系统样机,在20×放大倍数和物镜NA 0.75的条件下,验证了本文方法的有效性,在分辨率提升至1.8倍的同时视野可达1 380μm×1 035μm,所述空域超分重建算法能够大幅降低计算耗时。     

运动调制参考光实时全息测量位移方向研究

提出用物体运动调制参考光实时全息测量物体位移方向的理论、方法和技术。用一束近似平行的光照射贴有反射镜的物体,由两者分别反射到全息干版上的物光和参考光相干涉形成和记录实时全息图。用原记录光束照射全息图,使试件沿一定方向位移,通过实时全息图观察到的实时干涉条纹会随观察点的移动而移动。物体位移方向、干涉条纹位移方向和观察点位移方向之间有确定的关系,推导了这种关系的数学表达式。根据这种关系归纳出了测量物体位移方向的基本法则。用不同试件完成了测定位移方向的实验,验证了所提出的新理论、新方法和相应新技术的正确性。     

基于全息图放大的数字全息显微结构测量

针对典型预放大数字显微全息光路中存在的二次位相误差,本文设计了基于全息图放大的数字全息显微光路。此设计中,光束首先照射透明显微物体,然后与平行参考光干涉,形成全息图,最后经显微镜获得放大的全息图。这种光路从系统上直接消除了主要由球面波引起的位相畸变,有利于数字处理及实时化。作者以位相光栅(30 lines/mm,槽深约0.3 µm)作为实验样本,对此光路进行了分析研究,并分别用菲涅耳近似法和卷积法再现单幅全息图,同时获取了物体的强度信息和三维位相信息,位相深度的计算结果为0.27 µm。结果表明本文设计的光路对二次位相产生的离焦误差有明显的抑制作用。     

复合材料X射线实时成像检测关键参数分析

复合材料作为一种新型材料广泛应用于航空工业,而X射线实时成像检测则是用于复合材料零件的新型检测方法之一。本文着重分析了复合材料X射线实时成像检测中的放大倍数、灵敏度、灰度、分辨率、射线源至被测件的距离、管电压和管电流、散射线、缺陷/损伤尺寸与位置等关键参数,为获得优质的图像提供了基本的质量控制指标。     

Assessment of electron irradiation damage to biomolecules by electron diffraction and electron energy-loss spectroscopy

Electron radiation damage is one of the most severe problems in high resolution electron microscopy of biomolecules. The techniques of electron diffraction and electron energy-loss spectroscopy were applied to gain a better understanding of radiation damage in amino acids and nucleic acid bases. The results when compared with G-values for the release of ammonia and hydrogen sulphide from amino acids seem to indicate that bond scission is an important cause of radiation damage at moderate doses of irradiation. High resolution structural disorder in nucleic acid bases was found to involve loss of atoms peripheral to the main ring structure.     

Calculation of the variable-profile electron beam for electron coolers

Interaction of an electron beam with a cooled ion beam makes it possible to reduce its phase volume, perform accumulation of particles, and suppress various “heating” effects. The electron beam can also be used as a target for an electron-ion recombination reaction, which offers a chance to carry out atomic physics experiments and ensure slow uniform extraction of the ion beam from the storage ring. A high-perveance electron beam with a variable profile is required for effective cooling, while a high current density and a low energy of transverse motion of electrons in the beam is needed for extraction by means of recombination. It is shown that a convex cathode placed in a magnetic field can be used to form such a beam. A high current density can be attained with this shape of the cathode, but additional efforts must be focused on optimizing the gun’s optics in order to obtain a low energy of transverse motion of particles. Since ions repeatedly pass through the cooling section during their lifetime at different values of the betatron oscillation phase, the rates of recombination and cooling are dependent on the rms electron velocity averaged over the volume in which the beam interaction occurs. The proposed design of the gun with a convex cathode 10.2 mm in diameter ensures formation of a variable-profile electron beam with a nominal current of 1 A and a current density of 1.2 A/cm². The rms energy of Larmor gyration of electrons at the exit from the gun, averaged over the beam cross section (the “transverse” temperature) is 1 eV. A focusing electrode that forms the Pierce optics near the edge of the cathode, an electrode controlling the beam profile, and an anode are included in the optics of the electron gun.     

Biological applications of backscattered electron imaging of scanning electron microscopy

Backscattered electron imaging (BEI) of biological samples was already reported by Watanabe in 1972 (Watanabe 1984). Since then an increasing number of investigators has recognized the usefulness of this way of imaging and employed it not only as a complementary technique to cell surface viewing with secondary electrons but also for its unique analytical potential.     

Scanning electron microscope electron detector with a radial type discrete dynode electron multiplier

A discrete dynode electron multiplier with radial flux of electrons was built and tested in the range of low‐voltage scanning electron microscopy as a backscattered electron detector of topographic contrast. The multiplier collects backscattered electron emitted in a specific range of take‐off angles and over the whole azimuth angular range enabling large solid collection angle. Multipliers with different dynode shapes were studied theoretically with the use of the software for particle optics and three assemblies were built and tested experimentally. The gain estimation, assessment of the type of detected electrons (secondary electron or backscattered electron), imaging the spatial collection efficiency and signal‐to‐noise measurements were performed.     

Use of backscattered electron detector arrays for forming backscattered electron images in the scanning electron microscope

The backscattered electron (BSE) signal in the scanning electron microscope (SEM) can be used in two different ways. The first is to give a BSE image from an area that is defined by the scanning of the electron beam (EB) over the surface of the specimen. The second is to use an array of small BSE detectors to give an electron backscattering pattern (EBSP) with crystallographic information from a single point. It is also possible to utilize the EBSP detector and computer-control system to give an image from an area on the specimen--for example, to show the orientations of the grains in a polycrystalline sample ("grain orientation imaging"). Some further possibilities based on some other ways for analyzing the output from an EBSP detector array, are described.     

Some effects of electron channeling on electron energy loss spectroscopy

As an electron beam (of order 100 keV) travels through a crystalline solid it can be channeled down a zone axis of the crystal to form a channeling peak centered on the atomic columns. The channeling peak can be similar in size to the outer atomic orbitals. Electron energy loss spectroscopy (EELS) measures the losses that the electron experiences as it passes through the solid yielding information about the unoccupied density of states in the solid. The interaction matrix element for this process typically produces dipole selection rules for small angle scattering. In this paper, a theoretical calculation of the EELS cross section in the presence of strong channeling is performed for the silicon L23 edge. The presence of channeling is found to alter both the intensity and selection rules for this EELS signal as a function of depth in the solid. At some depths in the specimen small but significant non-dipole transition components can be produced, which may influence measurements of the density of states in solids.     

Detective quantum efficiency of electron area detectors in electron microscopy

Recent progress in detector design has created the need for a careful side-by-side comparison of the modulation transfer function (MTF) and resolution-dependent detective quantum efficiency (DQE) of existing electron detectors with those of detectors based on new technology. We present MTF and DQE measurements for four types of detector: Kodak SO-163 film, TVIPS 224 charge coupled device (CCD) detector, the Medipix2 hybrid pixel detector, and an experimental direct electron monolithic active pixel sensor (MAPS) detector. Film and CCD performance was measured at 120 and 300 keV, while results are presented for the Medipix2 at 120 keV and for the MAPS detector at 300 keV. In the case of film, the effects of electron backscattering from both the holder and the plastic support have been investigated. We also show that part of the response of the emulsion in film comes from light generated in the plastic support. Computer simulations of film and the MAPS detector have been carried out and show good agreement with experiment. The agreement enables us to conclude that the DQE of a backthinned direct electron MAPS detector is likely to be equal to, or better than, that of film at 300 keV.     

Nanotip electron gun for the scanning electron microscope

Experimental nanotips have shown significant improvement in the resolution performance of a cold field emission scanning electron microscope (SEM). Nanotip electron sources are very sharp electron emitter tips used as a replacement for the conventional tungsten field emission (FE) electron sources. Nanotips offer higher brightness and smaller electron source size. An electron microscope equipped with a nanotip electron gun can provide images with higher spatial resolution and with better signal-to-noise ratio. This could present a considerable advantage over the current SEM electron gun technology if the tips are sufficiently long-lasting and stable for practical use. In this study, an older field-emission critical dimension (CD) SEM was used as an experimental test platform. Substitution of tungsten nanotips for the regular cathodes required modification of the electron gun circuitry and preparation of nanotips that properly fit the electron gun assembly. In addition, this work contains the results of the modeling and theoretical calculation of the electron gun performance for regular and nanotips, the preparation of the SEM including the design and assembly of a measuring system for essential instrument parameters, design and modification of the electron gun control electronics, development of a procedure for tip exchange, and tests of regular emitter, sharp emitter and nanotips. Nanotip fabrication and characterization procedures were also developed. Using a "sharp" tip as an intermediate to the nanotip clearly demonstrated an improvement in the performance of the test SEM. This and the results of the theoretical assessment gave support for the installation of the nanotips as the next step and pointed to potentially even better performance. Images taken with experimental nanotips showed a minimum two-fold improvement in resolution performance than the specification of the test SEM. The stability of the nanotip electron gun was excellent; the tip stayed useful for high-resolution imaging for several hours during many days of tests. The tip lifetime was found to be several months in light use. This paper summarizes the current state of the work and points to future possibilities that will open when electron guns can be designed to take full advantage of the nanotip electron emitters.     

Secondary electron emission in the scanning electron microscope

The secondary electron emission induced by electrons in the energy range 2.5–25 keV was measured in a SEM. Values of the emission coefficient for C, Al, Cu, Mo, Ag and Au are presented showing that it varies systematically with atomic number. The coefficient is still appreciable at 25 keV beam energy. The signal from the secondary electron collector in the SEM includes large contributions from sources other than secondary electron emission from the specimen. These contributions are discussed and their relative importance measured. Physics Abstracts classification numbers: 0.690, 8.900     

Automated electron tomography with scanning transmission electron microscopy

We report the successful implementation of a fully automated tomographic data collection system in scanning transmission electron microscopy (STEM) mode. Autotracking is carried out by combining mechanical and electronic corrections for specimen movement. Autofocusing is based on contrast difference of a focus series of a small sample area. The focus gradient that exists in normal images due to specimen tilt is effectively removed by using dynamic focusing. An advantage of STEM tomography with dynamic focusing over TEM tomography is its ability to reconstruct large objects with a potentially higher resolution.