Application of fringe shifting technique in speckle photography

It is shown that the fringe shifting technique can increase the sensitivity of speckle photography for sub-speckle size changes. The technique gives time-ordered pattern that can be used for the sign detection of the motion as well.     

用数字滤波消除散斑条纹图噪声

本文讨论了散斑摄影条纹图的噪声来源及模型,设计合适的数字滤波器.采取正交实验手段,全面分析了噪声、条纹对比度和密度对条纹方向及间距测量精度的影响.     

一种用于自动分析散斑摄影条纹图的数字图像复原技术——衍射晕影响的消除

本文提出了一种消除衍射晕非均匀照度影响、提高计算机自动测量散斑摄影条纹图精度的数字图像复原算法.简单介绍了散斑摄影条纹的自动分析过程.在VAX-11/785计算机上对模拟的无噪声白光散斑条纹进行验证,结果表明,本算法和程序是可靠的.     

散斑条纹的快速高精度处理技术

本文提出一种快速高精度散斑杨氏条纹(斑纹)场处理方法——同态阀值滤波法。用它实现了散斑场条纹的快速、逐点连续高精度处理。     

旋转孔径散斑照相逐点分析法

本文提出了旋转孔径散斑照相的逐点分析法,其杨氏花纹一般来说不是等距离的直条纹,而是与位移的动态过程相联系的曲线条纹.本文解释了这种条纹的意义,给出了理论分析和实验证明.     

偏振孔径散斑照相法

本文讨论了偏振片在散斑照相多孔法中的作用,提出了一种新的散斑照相孔径——偏振四孔。     

Velocity contours by speckle photography

We describe a method of generating velocity contours of an object using speckle photography. The object is illuminated by a series of laser pulses following each other at equal intervals. A speckle record of the object is observed in a spatial filtering setup with a small aperture in the frequency plane. A fringe pattern representing a map of velocity contours is obtained in the output plane.     

白光数字散斑照像术

本文提出一种新的数字散斑计量术——白光数字散斑照像术.它以两维数字偏心滤波技术实现全场信息的表征,而以数字相关技术实现点信息的表征.文中给出了计量方法、理论分析及实验结果.     

激光散斑摄影术实验

将激光散斑摄影术设计成一个近代物理实验,用于测试位相物体的厚度。这一方法概念新颖、光路设计简便易行,且具有实用价值。在改造和创新近代物理实验方面,这是可取的,本文介绍相关的实验原理、光路设计及其实验内容。     

Speckle photography combined with speckle interferometry

By combining speckle interferometry (SI) measurements with speckle photography, the fringe visibility can be kept high despite the presence of a large bulk or rotating motion of the object. This combined technique improves the usability and measuring range of both pulsed and phase-stepped SI-methods. This paper reviews the theory of fringe formation in SI and shows some recent applications of this combined technique.     

Two-dimensional vibrations analysed by speckle photography

Speckle photographs of a laser-illuminated surface vibrating in its own plane give characteristic diffraction spectra. These have been investigated for a surface vibrating sinusoidally along two mutually orthogonal directions with equal amplitudes but differing frequencies. The diffraction patterns obtained are interpreted in terms of the Lissajous figures traced out by each speckle, taking into account the time-of-dwell of a speckle at any point on its trajectory. Results are given for frequency ratios of the two vibrations of 1:1, 2:1, 3:1. 4:1, and for non-integrally related frequencies.     

Digital speckle photography and speckle tomography in heat transfer studies

The line-of-sight speckle photography of transparent media is used for quantitative measurements of the instantaneous temperature fields in 3D unsteady flows. Both electronic and photographic methods are employed for specklegram recording. The subsequent specklegram treatment uses the Young's fringes method as well as cross-correlation analysis of small interrogation areas of the recordings. Experimental data for three different heat transfer configurations are obtained and discussed. The first one is natural convection over extended vertical heated plates with forward facing steps, the second is unsteady 3D convective flow around a suddenly heated vertical thin wire, and the third one is a convective plume above a multi-jet flame. Both local and global Nusselt numbers are determined via measuring local surface temperature gradients for these convective flows. The results are compared with Ostrach's theory for a single vertical plate and with the data obtained by Mach–Zehnder interferometry. The 3D temperature fields are reconstructed for axisymmetric convective flows around a suddenly heated vertical wire using quasi-double projection measurement and the Radon inversion. 3D temperature distributions above the combustion zone are reconstructed using multi-projection speckle photography measurements and computerised tomography.     

Automatic analysis of Young''s fringes in speckle photography and particle-image velocimetry

Laser-speckle photography (LSP) and particle-image velocimetry (PIV) are two closely related optical techniques for the measurement of two-dimensional in-place displacement. LSP is primarily used for the measurement of solid-surface motion, whereas PIV is used in fluid-flow applications. In both cases, data are obtained from the optical-power spectrum of a double-exposure recording of the moving object by measuring the wavelength and orientation of Young's-type fringes corresponding to the displacement magnitude and direction, respectively. Typically, in any single experiment, of the order of 10⁴ fringe patterns must be analysed, and this would be extremely tedious to perform manually. For this reason, a number of schemes have been reported in the technical literature for automated analysis of Young's fringes. In this paper, we examine two techniques, 1-D integration and 2-D autocorrelation, and discuss their application to LSP and PIV. A unified theoretical model is used to show important differences between the two techniques, and resulting implications with respect to analysis procedures are discussed.     

Super-resolution digital speckle photography for micro/nano measurements

Speckle photography, also referred to as one-beam speckle interferometry, has gone through several evolutions. It started as laser speckle photography and then white light speckle photography and recently the electron speckle photography. With the advent of CCD and computational power of PC, the process of recording also changed from optical (i.e., photographic) to digital. This paper presents some recent development of super-resolution digital speckle photography with the emphasis on micro/nano measurements.     

Application of correlation speckle photography for measuring contact pressures

A method for measuring contact pressures based on the measurement of irreversible changes in a surface microrelief by the speckle photography technique is presented. The analytic dependence between the change in the contrast of the carrying Young’s fringes and the relative area of change in the microrelief is considered. An example of a contact interaction between a cylinder end and a flat slab, the latter with a specially produced regular roughness on its contact surface, is used to experimentally verify the relation between the irreversible change in the roughness, the change in the contrast of the holographic interference fringes, and the change in the contrast of the carrying Young’s fringes. It is shown that the sensitivity of correlation speckle photography is higher than the sensitivity of the correlation holographic interferometry technique.     

Thermoplastic photographic material for vibration measurements by speckle photography

In order to measure vibration amplitudes by speckle photography in quasi real-time, the feasibility of using thermoplastic photographic material for recording a speckle pattern image is studied experimentally to be proved true. An optimum recording condition of the material is also obtained.     

Applications of laser speckle photography for thermal flow problems

Laser speckle photography measures projected beam deflection of a phase object. The beam deflection measured at the solid surface will directly determine the wall-temperature gradient. Thus, the laser-speckle photography allows the evaluation of the convection-heat-transfer coefficients without the need to correct for conduction and radiation heat losses, which otherwise would be necessary. Selected results and brief discussions are presented for several natural convection-heat-transfer problems. Second, high-temperature applications of laser speckle photography shows potential as a nonintrusive means of measuring flame temperature. A fairly good agreement is shown in comparison of the laser speckle data with intrusive thermocouple data. Suggestive discussions are made to further improve the accuracy and sensitivity of the laser speckle photography technique in high-temperature applications. Finally, tomographic reconstruction of laser speckle photography data is discussed using both actual test fields and computer-synthesized phantom fields. The conventional algebraic reconstruction technique (ART) has been modified to apply for the laser speckle tomography. The efficacy of ART is examined particularly under a limited number of projections.     

旋转孔径锥镜剪切散斑照相法

本文提出利用旋转孔径和锥镜进行剪切散斑照相,研测动态问题.该法能在一张散斑图上记录下物体动态变形的全过程,在全场滤波时可得到任意时刻的瞬态位移偏导数场.     

Some recent advances in electronic speckle photography

Major advances in electronic speckle photography are reviewed. Topics include the correlation properties of laser speckles, the principles and expected accuracy of electronic speckle photography, the effect of the digital recording and evaluation, and some recent applications. These applications involve two techniques for the measurement of 3D deformation fields, measurement of the in-plane strain field components using defocused laser speckle, and measurement of object shape.     

The identification of fringe positions in speckle patterns

This paper two methods of identifying fringe positions in speckle patterns. The first uses local directional averaging to track fringes, while the second uses standard image processing techniques to connect the patterns into a form where the fringes can be identified.