A new method of noncontact gauge block calibration using the fringe counting technique: II. Experimental verification

An experimental verification of a new noncontact interference method for gauge block or length bar calibration is presented. In this technique, the length of the tested artifact is measured by means of the counting fringe method. A new technique for central interference fringe detection is used for evaluation of the end surface positions of the measured artifact. The experimental set-up and length measurement procedure are described. Preliminary experimental results and uncertainty analysis of the proposed method are presented.     

An automatic processing technique for accurate surface form measurement

A single shot algorithm using a Fizeau interferometer was used to measure the form profile of a spherical smooth surface by means of fringe thinning process, which plays an important role in fringe patterns analysis. In this paper, an automatic processing technique based on the fringe thinning process is presented. The circular interference fringe pattern of the spherical smooth surface captured by the Fizeau interferometer was corrected by using the flat fielding method and then processed. Based on the fringe thinning and the assignment of the fringe orders, the information on the fringe feature was recovered automatically and the interference wavefront was reconstructed by the Zernike polynomial fitting method. The results were compared with the results measured by Bünnagel method, and the results were in good agreement. This means that the single shot algorithm is reliable, fast, and less sensitive to vibration and turbulence in surface form measurements. Simulation fringes with the ray tracing technique were obtained to match the practical fringes.     

Polychromatic light interferometer for high-accuracy positioning

Superposition of different-wavelength, multimode- and single-mode laser diode beams is investigated to locate the fringe of zero interference order in a Twyman-Green interferometer. The possibility of central fringe detection using three multimode laser diodes or one single-mode together with a pair of multimode laser diodes is shown. If a single-mode laser diode is applied, a simultaneous fringe-counting technique for displacement measurement is available. The influence of the angle between wavefronts entering the interferometer is analyzed. A repeatability of about 5 nm is shown for surface position determination when using three-beam source.     

Study on an automatic processing technique of the circle interference fringe for fine interferometry

The fringe center method (FCM) is an important digital processing technique of fringe patterns analysis for interferometry. In this paper, an improved automatic processing technique based on FCM was presented, which correlated the processing link and the looped feature of the circle fringe pattern. It also integrated several techniques including noise removal, the fringe thinning, the fringe patching, assignment of the fringe orders and wavefront reconstruction and can be executed orderly and automatically. Based on the new the algorithms of the fringe patching and assignment of the fringe orders, the fringe feature information was extracted automatically and the interference wavefront was reconstructed by Zernike polynomial fitting method. With the automatic processing technique, the circle interference fringe of the fine polished aluminum disks surface captured by the Twyman-Green interferometer was processed, and the surface profile and the parameters of the disk were obtained automatically. The experiments show that the improved automatic processing technique was more accurate and fast in measurement than the conventional one. It was convenient to use it in in-situ industry inspection.     

基于双声光偏转器的变频三维数字成像

提出了一种基于双声光偏转器的时序变频三维数字成像系统.此系统可以实时产生并投射具有不同空间频率的条纹结构光序列照明被测物体,可以以视频速率完成任意形状物体的三维传感.整体系统采用全固态结构,无任何机械运动部件,具有高精度、全场测量、动态可编程、普适性好等特点.给出了该三维数字成像系统对一个台阶状物体形貌测量的应用实例.结果证明DAOP对于解决具有复杂几何形状或拓扑结构物体的三维形貌测量问题是一种有效技术.     

Variable wavelength interferometry of birefringent retarders

A new interferometric procedure is proposed for testing birefringent retarders. The procedure uses monochromatic light with a continuously variable wavelength and two parallel pointer lines localized at a distance from each other in the fringe interference field of a double-refracting interferometer. The zero-order fringe of the empty interference field is brought into coincidence with one pointer line, and higher-order interference fringes displaced by an object under study are next brought into consecutive coincidence with the other pointer line as the wavelength of the monochromatic light is continuously varied.     

Using coloured structured light in 3-D surface measurement

The widest used algorithms for 3-D surface measurement using structured fringe patterns are phase stepping and Fourier fringe analysis. The techniques currently employed use mostly monochrome fringe patterns as a tool for phase information measurement and further surface reconstruction. However, the information contained in colour images is much more than that of monochrome, in this case, a new colour technique can be employed to analyse a measured scene with colour fringe patterns.This paper presents a new method for improving the measurement of 3-D shapes by using colour information of the measured scene as an additional parameter. The new method is based on primary colours (red, green and blue) to increase the number of the illuminated fringe patterns, which will remove or significantly reduce the common drawbacks of existing methods. The proposed technique produces a number of coloured structured lighting patterns, which are projected from different angles onto the scene. These patterns are analysed using masking algorithms, a specially adapted multi-colour version of the standard Fourier fringe analysis method and calibration routines. In this way a number of the standard difficulties are overcome.     

Two-Period Interference Fringe Interferometry for Step-Profile Altitude Difference Measurement

This paper proposes a new measuring method called two-period interference fringe interferometry, for a step-profile altitude difference measurement. The principle of the method is different from that of the two-wavelength interferometry which is widely known. The two interference fringes with only slight difference between their spatial periods are obtained by turning a binary step-grating, and they produce a synthetic equivalent period much longer than either of the two periods alone. The interference fringes are produced by the ±1st-order beams diffracted from the grating. The intensity distribution of the interference pattern is independent of the wavelength of the laser-diode light source used. The measuring range of this method is much larger than that of the two-wavelength interferometery. Sinusoical phase modulating technique is easily applied to detect the phase distribution of the interference pattern by vibrating the grating sinusoidally. A plane reflector of 3mm thickness is measured to verify this novel method.     

基于物体像的干涉条纹图像中散斑噪声的识别方法

散斑噪声是激光干涉时的普遍现象,其覆盖被测表面对应区域的形状信息,造成测量误差。针对斜入式激光干涉测量中散斑噪声的特点,提出一种基于物体像的散斑噪声的识别方法。该方法通过统计物体像中有效测量区域和背景区域内灰度分布的特点,自动计算出判定散斑噪声的上下阈值。基于物体像与干涉条纹图像间微米级的映射关系,得到干涉条纹图像中散斑噪声的位置。设计了相关实验,对干涉条纹图像中识别出的散斑噪声区域进行修补,消除了包裹相位图中一个条纹周期内相邻像素点间大于π的相位突变。     

干涉亮条纹强度的不均匀分布

建立了低频液体表面声波的激光干涉测量系统,实验上不仅得到了清晰、稳定的干涉条纹,而且首次发现干涉条纹的强度分布具有空间不均匀性,干涉条纹被限定在一定的空间区域内,中心干涉条纹强度最小,向两边强度逐渐增大,在两边界位置达到极大.根据波动光学原理,得到了干涉条纹分布的解析表达式,并给出了低频表面波振幅、波长与干涉条纹空间限度、干涉条纹间距的数学表达式.理论规律与实验结果吻合较好.     

热光的高阶双缝干涉

干涉效应反映了光场的相干性,非相干光源中无序性会破坏干涉.然而对于高阶干涉来说这一看法并不成立.文章作者最近的理论和实验研究表明,横向传播方向无序的热光源可以实现高阶双缝干涉.尽管单个探测器的强度分布是均匀的,处于不同位置的两个探测器的联合强度关联却出现了干涉条纹.当两个探测器同步反向移动时,条纹间距减小为一阶干涉条纹的一半.实验结果同不久前报道的在自发参量下转换过程中产生的纠缠双光子对的双缝实验中所观察到的亚波长干涉效应十分类似.实验结果可以用多模热光场的二阶空间关联性质来解释.热光的高阶双缝干涉是著名的Hanbury-Brown和Twiss实验的空间干涉版本,因此也可称其为Hanbury-Brown和Twiss型双缝干涉。     

A CCD-based polarization interferometric technique for testing waveplates

A CCD-based polarization interferometric technique is developed to test waveplates. A Babinet compensator is used to produce interference fringes for polarized input and the retardance introduced by the waveplate when inserted in the optical beam is calculated from the fringe shifts using the phase matching technique. A theoretical model is fitted with the observed fringe shifts to get an accuracy of 0.5° in the retardance calculation. The experimental set-up and the measurement of retardance for zero-order and high-order quarter waveplates are discussed. The retardance calculation for a zero-order waveplate is found to be more accurate than the high-order waveplate. This technique can also be used to measure an arbitrary amount of retardance produced by any birefringent waveplate and also to determine its optic axis direction.     

Analysis of moiré fringes for measuring the focal length of lenses

We describe a technique based on fast Fourier transform and least-squares fit for automated analysis of moiré fringe patterns for accurately measuring the focal length of lenses. An interference fringe pattern is produced by a reflective diffraction grating interferometer and illuminates the test lens. Moiré fringes are generated by digitally superimposing the magnified fringe pattern imaged by the lens on the interference fringe pattern without the test lens. We analyze two common ways to generate the digital moiré effect: multiplication and subtraction with successive rectification of the two digitally stored intensity distributions, and we show that in the latter case by means of the described technique it is possible to determine the moiré spatial frequency by a simple and fully automated procedure.     

A genetic optical interferometric inspection on micro-deformation

This paper describes a feasibility study of an optical method for measuring nanoscale deformation of micro-components that are commonly employed in the field of microelectromechanical systems (MEMS). Both theoretical and experimental results demonstrate that an optical interference fringe pattern resulted from an air gap consisting of two surfaces (object and reference surfaces) is a simple function of the deformation of the micro-component. A microscopic system incorporating a coaxial monochromatic light illumination and a high resolution CCD sensor is utilized to record the interference fringe pattern. The experimental results on different micro-components show that the proposed technique is applicable to the deformation measurement on micro-components of MEMS devices.     

一种新型干涉选择调幅光谱仪的研究

讨论一种新型干涉选择调幅光谱仪的光路设计，利用补偿板的扭动实现振幅调制。文章同时对幅射通量和分辨率进行了理论分析，采用矩形光栏时，分辨率为光栅分辨率的１．３５倍。文章还讨论了采用椭圆形光栏时，仪器函数曲线的切趾。     

条纹扫描干涉测试技术及其应用

系统地叙述条纹扫描干涉测试技术的原理及公式推导过程;介绍我院正在研制的条纹扫描剪切干涉仪的工作原理。     

Center positioning of circular interference fringe patterns for fine measurement

A kind of center positioning method of the circular interference fringe patterns was reported in this paper. The whole process was programmed by Matlab for processing the gray-scale images without denoising preprocessing and binary format transformation. The gradient vector field (GVF) based on a complex-valued cost function was used to extract the skeletons of circular interference fringe patterns, and the coordinate of the center was calculated by statistical method in which partial skeletons were selected to calculate the center according to the space topological relationship. Finally, subpixel accuracy and perfect anti-noise ability of the proposed method are demonstrated by the simulation and experimental fringe patterns, respectively. Thus the technique can be used in precision measurement and fine interferometry.     

基于正弦条纹投影的三维传感及其去包裹处理

采用液晶显示（LCD）投影仪产生的正弦条纹,用四步相移技术对物体进行了三维形貌测量,重点讨论了去包裹问题,对大面积相位间断区的模板标识及含离散相位间断点条纹图的去包裹总是提出了新的处理方法,给出了实际测量及计算结果。     

Real-time color holographic interferometry devoted to 2D unsteady wake flows

A new optical technique based on real time holographic interferometry in true colors has been implemented around the transonic wind tunnel of the ONERA-Lille center to analyze 2D unsteady wake flows. Tests realized in color interferometry, real time and double exposure, use simultaneously three wavelengths of a continuous waves laser (argon and krypton mixed) and holograms are recorded on silver-halide single-layer panchromatic Slavich PFG03c plates. The very principle of real-time true color holographic interferometry uses three primary wavelengths (red, green and blue) to record, under no-flow conditions, the interference among the three measurement beams and the three reference beams simultaneously on a single reference hologram. After the holographic plate is developed, it is placed on the test setup again in the position it occupied during exposure and the hologram is illuminated again by the three reference beams and three measurement beams. A flat, uniform color can then be observed behind the hologram. So a horizontal, vertical, or even circular fringe pattern can be formed and the achromatic central fringe can be made out very clearly. The single color is used to determine the path difference zero on the interferograms. The flow studied was the unsteady flow downstream of a cylinder placed crosswise in the test section. A sequence of hundred interferograms was recorded on the flow around the cylinder at Mach 0.37. The vortex formation and dissipation phases can be seen very clearly, along with the fringe beat to either side of the cylinder.     

结构光照明显微中的偏振控制

结构光照明显微(structured illumination microscopy.SIM)作为一种宽场超分辨光学显微成像技术,具有成像速度快、光漂白和光毒性弱等优点,是目前主流超分辨成像方法之一.在SIM技术中,正弦强度分布的条纹结构光场的对比度决定了SIM超分辨图像的质量.低的条纹对比度将导致样品中超衍射极限的高频信息被噪声掩盖,从而无法解析出超分辨信息.结构照明入射光的偏振态调控决定了干涉条纹的对比度,是SIM的关键技术.鉴于此,本文总结对比了几种典型的SIM系统偏振控制方法,同时提出了一种使用零级涡旋半波片的偏振控制方法.实验证明,与其他方法相比,采用零级涡旋半波片法可以获得更高效的偏振控制效果,具有系统结构简单、易使用、可将光能利用率提升到接近100%的优点.