基于电子散斑干涉与数字剪切散斑干涉法的悬臂薄板振动分析

基于激光光路的光波随机相位扰动,分析了电子散斑干涉实时图像相减时模态条纹图的形成机理,提出了一种振幅涨落测量法。搭建了用于离面振动分析的电子散斑干涉和数字剪切散斑干涉测量系统,并对完整和含狭缝的悬臂铝板的振动特性进行了实验研究。实验结果表明,实时图像相减模式获得的模态条纹图对比度明显优于其他方法,得到的前10阶模态条纹图与有限元法计算结果具有良好的一致性。相比于电子散斑干涉法,数字剪切散斑干涉法对试样局部的刚度变化和缺陷更敏感。     

线性相关计算形成数字剪切散斑相关条纹图

本文提出了用线性关计算法形成数字剪切散斑干涉纹的新方法，从理论分析和实验研究均证明，用该方法所获得的数字剪切散斑相关条纹图在图象监视器上易于观盾，条纹图象光强无直流分量影响且可见度较减模式要高，该新方法的采用为今后的条纹图象分析了奠定了基础。     

剪切散斑干涉术的统计分析

本文用统计光学方法分析了剪切散斑图的成象过程;散斑图的频谱分布以及全场滤波干涉条纹的形成.发现剪切散斑干涉条纹不仅与三维位移微分有关,而且与面内位移量有关.在此基础上又讨论了影响干涉条纹质量的有关因素,并作了实验验证.     

线性相关计算法形成数字剪切散斑相关条纹图

本文提出了用线性相关计算法形成数字剪切散斑干涉条纹的新方法,从理论分析和实验研究均证明,用该方法所获得的数字剪切散斑相关条纹图在图象监视器上易于观看,条纹图象光强无直流分量影响且可见度较减模式要高,该新方法的采用为今后的条纹图象分析奠定了基础。     

频闪剪切散斑干涉术的研究

提出了一种用于振动研究的方法——频闪剪切散斑干涉照相法。该方法由于采用了剪切镜,能得到较为精确的散斑剪切图,提高了测量的精度,是一种用于振动研究较为理想的散斑照相的新方法。讨论了频闪剪切散斑干涉术的基本原理,给出了频闪剪切散斑图的全场分析的平均光强分析的解析式,并给出了实验结果。理论和实验都表明频闪剪切散斑干涉照相法要优于时间平均剪切散斑干涉照相法。该方法在全场滤波分析时,能给出任一瞬时物体振动信息,得到清晰的、高衬比的全场干涉条纹图,是一种实用可行的方法。     

剪切散斑干涉术的无损检测研究

剪切散斑干涉术用于复合材料的光学无损检测具有较宽的加载范围,便于实现缺陷的全场记录,防止漏检。本文从理论上推导了剪切散斑干涉条纹(等应变条纹)的强度分布,并证明随着加载量的增大,条纹变密的程度较全息干涉条纹(等位移条纹)缓慢。加之,剪切散斑干涉条纹灵敏度具有可调性,加载范围大为加宽。实验观察与理论分析一致。     

旋转剪切散斑干涉法的研究

本文提出一种新的动态散斑照相法——旋转剪切散斑干涉法.文中给出了理论分析和初步的实验结果.该方法不仅能在一张剪切散斑图上记录物体动态变形的全过程,而且在全场滤波分析时能方便地给出任一瞬时物体的变形信息,得到清晰的、高衬比的干涉条纹图.该方法设备简单,用途广泛.     

数字剪切散斑干涉术中的刚体位移补偿的新方法

给出一个数字剪切散斑干涉术中的刚体位移补偿的新方法，当刚体位移大于一个像素时，加载前后的散斑图将会由于位置的变化导致失相关，重新安排每一个像素将会克服此失相关，散斑平均、条纹重构以及迭代方法用来改善条纹质量，消除散斑噪声，最后得到可取结果。     

数字剪切散斑干涉法研究铝合金中Portevin-Le Chatelier带的离面变形行为

作为Portevin-Le Chatelier(PLC)带的重要特征之一,其离面变形仍缺乏实验研究.本文提出使用数字剪切散斑干涉法研究GB6061铝合金中PLC带的离面变形.通过图像相减得到的条纹图,实时观察了PLC带的几何形貌和传播过程,并获得了PLC带离面位移分布.在1/15 s内,PLC带的最大离面位移为245 nm,位置偏向于PLC带传播的前沿.在条纹图中,PLC带传播前沿的亮条纹始终较窄.此外,实验还观察到PLC带位置变更和倾角转向的演化过程.实验表明,数字剪切散斑干涉法具有高灵敏度和防震性,是研究PLC带离面变形简便有效的方法.     

数字剪切散班干涉术中的刚体位移补偿的新方法

给出一个数字剪切散斑干涉术中的刚体位移补偿的新方法。当刚体位移大于一个像素时，加载前后的散斑图将会由于位置的变化导致失相关。重新安排每一个像素将会克服此失相关。散斑平均、条纹重构以及迭代方法用来改善条纹质量，消除散斑噪声，最后得到可取结果。     

数字散斑法在局域剪切带三维变形研究中的应用

在适当的温度、应变率和预变形下,合金材料的拉伸试验中,将会出现伴随应力锯齿形跌落的雪崩式剪切变形带,即波特文-勒夏特利埃(Portevin-Le Chatelier,PLC)效应。利用高速数字摄像系统(分辨力1000 frames/s)并结合数字散斑干涉法(Digital speckle pattern interferometry,DSPI)和数字散斑相关法设计了一套光学变形测量系统,实现了拉伸试验中对试件表面三维变形的实时、精确测量。利用该光学系统对铝铜合金试件在拉伸试验中产生的跳跃传播的局域剪切带瞬态成核过程进行捕捉。通过结合数字散斑相关法得到的面内变形定量结果和数字散斑干涉法得到的表现离面变形的条纹图,再现了剪切变形带成核和传播瞬间的三维变形过程。     

Measurement of curvature distribution using digital speckle three-shearing aperture interferometry

Digital speckle three-shearing-aperture interferometry used for the measurement of curvature distribution fields of a deformation object is proposed for the first time. In this method, pure curvature distribution fringes without containing slope distribution fringes can be obtained by using digital speckle three-shearing-aperture interferometry. Two specklegrams, one before and the other after object deformation, are recorded by a CCD camera and stored in a computer. A 2-D fast Fourier transform (FFT) and a 2-D inverse FFT (IFFT) are performed on the two specklegrams. The subtraction of the transformed specklegrams will produce curvature distribution fringes, and the speckle noises in curvature distribution fringes can be removed after these fringes pass through low-pass filtering. Results from theory and experiments are in good agreement.     

Study and design of exponential and Butterworth low-pass filters used for digital speckle interference fringe filtering

This paper studies the exponential and Butterworth low-pass filtering methods and proposes improved exponential and Butterworth low-pass filters. The improved low-pass filters proposed in the paper can be used effectively for filtering processing of digital speckle interference fringes obtained in digital speckle pattern interferometry. Both theoretical analysis and experimental results are presented in the paper.     

Analysis of reflection speckle holograms in a BSO crystal

A theoretical and experimental study of speckle registering in photorefractive BSO crystals through reflection hologram geometry is implemented. The three-dimensional speckle nature is considered in the diffraction efficiency calculations. The interference process produces index-of-refraction gratings in the speckle volume via the photorefractive effect. It is demonstrated that the coupled-wave theory for reflection geometry allows explaining the diffraction efficiency behavior when the interaction length is properly taken into account. It means that the speckle depth is related with the interaction length. The speckle depth can be controlled by the imaging system pupil aperture diameter. Under this condition, the influence of the speckle depth on the diffraction efficiency is analyzed. An agreement between the numerical model based on the coupled-wave theory and the experimental results is obtained.     

Speckle-pattern interferometry applied to the study of phase objects

If a speckle pattern is photographed through a phase object, the individual speckles are displaced over varying distances depending upon the phase irregularities in the object. A double exposure is made, the object being present during one of the two exposures only. When the processed photographic plate is observed through an aperture stop in the Fourier transform plane, interference fringes representing contours of the optical path gradient are obtained. The sensitivity of the method and the direction along which the gradient is measured can be varied by modifying, respectively, the distance of the Fourier-plane aperture from the optical axis and its azimuth.     

Achromatic stellar interferometry

One drawback of Michelson's stellar interferometer is due to the fact that the period of the interference fringes is proportional to the wavelength. Hence, in broadband light the fringe contrast is low, or in narrowband light (after filtering) the luminosity is low. We propose a modified stellar interferometer with perfectly achromatic fringes, that has better light efficiency and better signal to noise under most circumstances. To that end, two pieces of grating have to fill the two apertures of Michelson's setup. Achromatic interference fringes occur somewhere along the system axis, where the plus-first diffraction order from one aperture meets the minus-first diffraction order from the other aperture. Laboratory experiments confirm the predicted achromatic performance.     

Measuring velocity of speckle fields with digital speckle pattern interferometry

We investigate a digital method for detecting the velocity of a diffusing object. The technique is based on Digital Speckle Pattern Interferometry (DSPI). A set of reference fringes is generated externally through the reference beam in a digital interferometer. As the object moves, subsequent frames are acquired and subtracted according to the normal DSPI procedure and stored. By means of the theory of first order speckle statistics applied to speckle intensity correlation, we relate the visibility variations in the reference fringes with the object velocity. Thus, by measuring the fringe visibility variation in the resulting DSPI stored frames the mean object velocity can be obtained. The theoretical results are experimentally verified.     

Verification of speckle contrast measurement interrelation with observation distance

The speckle contrasts of two types of laser projectors were measured at various observation distances and observation lens pinhole diameters using a quantitative measurement technique. We found that the speckle contrast as a function of the observation numerical aperture varies with the projection architecture. In a full-frame projector, it is proportional to the numerical aperture, but it is proportional to its square root in a raster-scanned projector. The difference in speckle contrast as a function of the numerical aperture was analyzed based on Goodman’s speckle theory. The obtained results were found to be very useful and applicable for speckle evaluation and display qualifications in an arbitrary observer’s position.