基于干涉条纹跟踪实现纳米级位移测量的方法研究

设计了一套干涉条纹图像实时采集处理系统。在分析迈克尔逊干涉条纹特征表象的基础上 ,给出了通过跟踪干涉条纹的移动量测量被测对象纳米级位移量的理论公式 ;提出了干涉条纹特征点的提取与跟踪算法 :分段线性变换、方形窗口中值滤波和门限化边缘提取 ,给出了基于统计学原理的通过计算多条干涉条纹移动量获得被测对象纳米级位移量的计算公式。实验结果表明了该方法的有效性和实用性     

Lens Sag Measurement of Microlens Array Using Optical Interferometric Microscope

This study attempted to develop a detection system for lens sag of the microlens array in real time using an optical automatic inspection framework to link with the computer through a camera. An image processing technique was applied to detect the spherical microlens array, and then, the results were compared.The system light source used laser light and applied CCD to collocate with the microscope array to form an automatic optical detection system for an optical interferometric microscope. It applied the principle of the Fizeau interferometer, illuminated the surface of microlens array, and formed the phase difference required by the interference of two lights through the laser light reflected by the reference plane and the surface of the microlens array, thus, forming an interference fringe.When the sag of the microlens was much longer than the wave length of the detection light source, the fringe would be densely distributed, thus, only a few central fringes were clear in the microscopic image. An image processing method was used to search the center of the interference fringe and a creative algorithm was utilized to obtain the lens sag of the microlens. As proved by the experiment, lens sag of 4 microlens arrays were detected in real time, with a minimum detection error of 0.08 μm, and a maximum detection error of 4 μm (error value 1 ~ 9%), according to different sample processes. This system featured a simple structure and is applicable to non-contact detection and detection of different-sized microlens arrays.     

Measurement of vibration amplitude by an optical fiber-based moiré interferometer

A projected-fringe fiber-based moiré interferometer is proposed to measure the local amplitude vibration of a diffuse surface. The technique is based on an optical fiber interferometer which projects interference fringes on the object surface. The visibility of these carrier fringes is modulated by a function of local amplitude vibration. Full-field quantitative analysis is performed by analyzing the fringe pattern with a 2-D Fourier transform method. Theoretical details, and experimental results are presented.     

Simultaneous measurement of surface shape and absolute optical thickness of a glass plate by wavelength tuning phase-shifting interferometry

The absolute optical thickness and the surface shape of a glass plate of 7-in. square and 3.1mm thick was simultaneously measured by three-surface interferometry using a wavelength tuning Fizeau interferometer. The wavelength of a tunable diode laser is scanned linearly from 632 to 642 nm, at which the initial and the final phases of the interference fringes for the surface shape and for the optical thickness were separated and measured by a tunable phase-shifting technique. The number of phase variations in the interference fringes during the scanning is counted by discrete Fourier analysis, in which systematic errors caused by a nonlinearity in the wavelength scanning is corrected by a correlation analysis between the observed and theoretical interference fringes. Experimental results demonstrate that the systematic errors in the measured value were 15 nm for the surface shape and 0.6 μm for the absolute optical thickness.     

电子散斑干涉条纹骨架线提取的新方法

电子散斑干涉条纹的强噪声特性使其信噪比过低，常用的图像二值化、细化等算法对散斑干涉条纹的骨架提取都存在一定的不足，文章在对散斑条纹图像平滑去噪、对比度增强的预处理基础上，对其进行边缘提取、填充、细化，从而得到干涉条纹的中心骨架线，提出一种基于MATLAB的散班图像自动处理算法。结果表明：文中提出的干涉条纹的细化方法可以准确地找到骨架线，为获得面内位移场的等位移线图提供了一种新方法。     

Fizeau型偏振移相干涉仪的实验研究

研究了一种Fizeau型偏振移相干涉仪。以中心波长为650nm的多纵模半导体激光器作为光源,利用光源的短相干特性和一套偏振延迟装置分出一对偏振方向正交的参考光和测试光,采用巴比涅-索列尔补偿器作为偏振移相器。测试了一块平行平板的前表面面形,面形PV值为0.0682λ,RMS值为0.0127λ。该方法的优点是移相精度高,移相时无须推动参考镜,适用于大口径光学系统的干涉测试,可消除多表面干涉杂散条纹的影响。     

Measurement of surface form deviation of the plane optical element using grid line method

A method for automatically measuring the surface form deviation of the plane optical element is presented. It uses the image pre-processing technique to obtain the centerlines of the interference fringes, the grid line technique to search the average fringe spacing and the maximum curvature of the interference fringes, and the normalization to obtain the value of surface form deviation of the optical element. The experimental results show that the measuring precision of the surface form deviation of the plane optical element reaches the value of 0.1 and the method improves the adaptation capability of processing the interference fringes, which indicates that the method can substitute the visual interpretation of interference fringes in high-noise workshop environment.     

Highly accurate film thickness measurement based on automatic fringe analysis

This paper describes an automated multiple-beam interferometry for measuring a calibrated step height of (27.00 ± 3.00) nm nominally. The fringes captured from the multiple-beam Fizeau–Tolansky interferometer were thinned by using a written program to obtain accurate measurement. We claim that multiple-beam interferometry based on automatic fringe thinning process can provide a real time solution for calibrating step heights precisely and with high accuracy. The uncertainty budget of the multiple-beam interferometry method due to incomplete parallelism of the incident beam and the inhomogeneity of the reflecting layers was calculated automatically with a written ray tracing program. The uncertainty budget in multiple-beam interferometry was estimated to be of the order of 3.00 nm.     

基于菲佐干涉仪测风激光雷达的误差分析

详细分析了基于菲佐(Fizeau)干涉仪测风激光雷达利用条纹重心法反演风速时的方法误差和系统噪声引起的测量误差。提出了方法误差的修正方法,推导出了测量误差理论公式。并用蒙特卡罗方法模拟了低对流层的回波信号,并对其进行条纹重心法风速反演。结果表明:方法误差和气溶胶与分子后向散射比有关,噪声引起的测量误差与信号强度和气溶胶与分子后向散射比有关。在0~5 km,高度采用条纹技术测量的风速误差小于1 m/s。     

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.     

标准球面透镜的几何特性与误差分析

标准球面透镜是斐索型干涉仪的核心器件,综述标准球面透镜的几何特性和误差。分析标准球面透镜在干涉照明光路和成像光路中的作用,重点介绍并实验验证了球面干涉成像的R-sinθ几何特性关系模型,给出了采用Q非球面实现非球面分裂的新型设计方法,以及2片式非球面标准球面透镜结构的实例,概述了针对小F数标准球面透镜球面干涉腔中的待测球面调整误差和移相空间非均匀性误差的研究成果,介绍了校正球面干涉腔中误差的波面差分算法,指出在近标准球面透镜焦点位置测量球面时的回程误差影响,从物像共轭关系角度解释了近焦点位置回程误差较大的原因,比对分析了标准球面透镜的透射波前与斜率对回程误差的影响。提出了在设计标准球面透镜时需注意的几何特性关系,以及使用标准球面透镜时易产生的误差和相应的抑制方法。     

Measurement of residual wedge angle with a reversal shear interferometer

A technique for determination of residual wedge angle of high optical quality transparent parallel plate using a reversal shear interferometer-based optical system has been discussed. In this technique the parallel plate to be tested is used to introduce angular tilt in the preset two-beam interference fringes of a reversal shear interferometer. The parallelism is calculated from the angular tilt of the fringes. The technique is more sensitive compared to techniques using Fizeau interferometer and is most suitable for highly parallel transparent plate with very low residual wedge angle.     

Novel processing tools for automated doppler picture veocimetry (DPV) evaluation

A unique technique, the Doppler Picture Velocimetry (DPV), for measuring and visualizing velocities especially in hypersonic gas flows is presented. By means of a Michelson interferometer (MI) the Doppler shifted light scattered by tracers is transformed into an image showing Fizeau fringes. The image fringe distribution provides information on the Doppler frequency shift which is related to the velocity of the particles crossing a light sheet plane. To overcome former disadvantages of DPV, the optical set-up as well as the processing scheme have been improved significantly. Two schemes have been tested in recent times for fringe processing: 1) an alternative process, the Least Square Estimators (LES) and 2) an algorithm based on a technique using Fast Fourier Transformations (FFT) to examine the DPV images in the frequency domain. The new DPV algorithms now allow an automated calculation of the velocity profiles from the Doppler pictures without manual fringe tracing as it had to be done in the past. Both methods are compared by means of Mach 6 flows around a wedge and a sphere produced in the ISL high energy shock tunnel STA. TiO₂ particles are illuminated by a laser light sheet which was perpendicularly arranged to the main flow direction. Light observation via the MI from the side (90° to illumination) informs on the vertically oriented velocity through the DPV images.     

Phase retrieval of non-continuous fringe patterns by a genetic data reduction algorithm

In this work we focus on the possibilities of recovering the phase from a single fringe pattern that do not have a fringe order sequence or whose fringes are broken. The phase is obtained with a polynomial fitting method whose coefficients are calculated with a genetic algorithm technique that constrains the smoothness of the solutions of a merit function. It is explained how conjugate gradient methods fail in the solution of the proposed merit function. Experimental results are presented using discontinuous fringe patterns obtained from a grazing incidence interferometer while testing a polishing tool.     

Interferometric determination of refraction and dispersion of human blood-serum, saliva, sweat and urine

Multiple-beam interference fringes of equal chromatic order are produced in air and liquid sample interferometric gaps. The two gaps are of the same thickness and simultaneously enclosed in a wedge interferometer. A single shot interferogram containing fringes in the two gaps is sufficient to deduce the needed experimental data. Locations of the fringe maxima, in the two gaps, are introduced in a non-numerical procedure for determining the gap thickness and the liquid-phase refractive indices across the visible spectrum. The method has been used for measuring the phase refractive indices of human blood-serum, saliva, sweat, urine and water liquids. A third-order polynomial dispersion relation is applied for fitting the measured phase indices. Group refractive indices have been derived and fitted to the same dispersion formula.     

Curvature measurement using phase shifting in-line interferometry,single shot off-axis geometry and Zernike's polynomial fitting

This paper describes the difference between phase shifting in-line interferometry, single shot off-axis geometry and Zernike's polynomial fitting methods for measuring the curvature of a spherical smooth surface by using the Michelson interferometer. In phase shifting in-line interferometry, four interferograms shifted by a piezoelectric actuator (PZT) were captured by a digital detector and corrected by using the flat fielding method. In off-axis geometry, single shot off-axis interferogram was obtained by tilting the reference and the object wave of the off-axis interferogram was reconstructed in the central region of the observation plane by using the digital reference wave concept. The demodulated phase map was obtained and unwrapped to remove the 2π ambiguity. The unwrapped phase map was converted to height and the sagittal length that used for curvature measurement was calculated accurately. The results extracted from phase shifting in-line interferometry and single shot off-axis geometry methods were compared with the results extracted from single shot Zernike's polynomial fitting method and the results were in excellent agreement. A new trial was done to overcome the fringes produced from the object interfaces. Some factors of uncertainty which affected on the measurement were estimated in the order of 6.0 × 10^?5 mm or 0.003 dioptre (▽).     

Multiple-beam interference fringes applied to investigate the index profile of the optical fiber dip

A numerical-based phase shift method is presented to study optical fibers having a dip in the refractive index profile at the center of the core. Mathematical expressions for the shape of multiple-beam Fizeau fringes crossing a graded-index optical fiber (GRIN) comprising a central graded-index dip or GRIN fiber with a constant refractive index dip, immersed in a silvered liquid wedge, are derived. The index profile parameters of the central dip are determined by comparing the theoretical fringe shape across the fiber cross-section and the experimental fringe shape obtained from micro-interferograms of the wedge interferometer.     

Automatic refractive index profiling of fibers by phase analysis method using Fourier transform

Automatic fringe pattern analysis is a powerful and inexpensive digital image-processing technique. It is used to analyze the fringe pattern obtained by different optical techniques, such as multiple-beam Fizeau fringes. To perform accurate and fast automatic measurement of fiber refractive index profile, phase analysis method has been used with the Fourier transform technique. In this paper, the refractive index profiles of polyethylene fibers with different draw ratios are presented by two methods, fringe shift method and phase analysis method. A comparison between the results obtained is presented.     

基于干涉条纹图像对比法测量微位移

研究了基于迈克尔逊干涉条纹对比法测量微位移的实验。用He-Ne激光器、反射镜和分束镜组成的干涉光路,其中一个反射镜固定在被测物体上,通过被测物体的移动带动反射镜移动使干涉光路发生变化,从而导致干涉条纹的改变。在形成干涉条纹的位置利用线阵CCD采集干涉条纹图像,用序列图像对比的方法对图像进行处理和计算,得出被测物体的微位移。实验表明利用序列图像对比的方法测量微位移,方法切实可行、测量准确度高、测量的精度能够达到微米量级。     

Surface flatness of optical thin films evaluated by gray level co-occurrence matrix and entropy

The surface characteristics of titanium oxide films evaluated by gray level co-occurrence matrices (GLCMs) and entropy are demonstrated experimentally. A PC-based measurement system was set up to detect the interference fringe of optical coating surface as captured by a Fizeau interferometer. Titanium oxide films were prepared by an electron-beam gun evaporation method. The proposed measuring system was used to evaluate the surface flatness of titanium oxide films coated on glass substrates. The variation of entropy in titanium oxide films before and after film deposition was found to be related to the root-mean-square (rms) surface roughness. Surface characteristics of thin films were fast measured by our proposed method and the test results were verified by atomic force microscopy (AFM) and scanning electrical microscopy (SEM).