Optical extensometer and elimination of the effect of out-of-plane motions

A novel optical extensometer is developed to estimate the local uniform strain on planar surface accurately. The proposed system consists of a shared large format lens and two image sensors, which acquire pairs of images of two isolated small regions on the object surface simultaneously. Digital image correlation (DIC) algorithm is applied to determine the relative displacement between gauge points designated on recorded pairs of images. Then local strain can be extracted after dividing the relative displacement by the scale distance. Moreover, a special experimental setup called “correction sheet” is used to eliminate the virtual strain induced by out-of-plane motions. Uni-axial tensile experiments are performed to validate the reliability and resolution of the optical extensometer, and the measurement results demonstrate that the resolution of the optical extensometer achieves 2–3 με.     

用全息干涉法测量杨氏模量

通过对悬臂梁受力前后双曝光全息图进行再现，测量出干涉条纹序数与相对应的位置坐标，再利用最小二乘法求杨氏模量．     

云纹干涉法面内位移测量的光栅补偿方法研究

运用光的干涉与衍射理论，导出了对称入射光路云纹干涉法面内位移计量的基本公式。针对云纹干涉法在实际应用中易引入刚体位移对真实面内位移干扰这一棘手问题，设计了定量补偿面内位移和变形的非对称光栅补偿光路系统。由于采用高灵敏度基准光栅调节的方法，比螺旋测微器等纯机械方法具有众多优越性。本文分析了该补偿方法对面内正应变条纹梯度和面内剪应变条纹梯度的补偿原理和具体实施过程。本方法大大提高了云纹干涉法面内位移计量和补偿的可靠性。     

The separation of out-of-plane displacement from in-plane components by fringe carrier method based on large image-shearing ESPI

A fringe carrier method for separating out-of-plane displacement from in-plane components based on large image-shearing electronic speckle pattern interferometry (ESPI) is presented. If the test object is respectively illuminated by two expanded symmetric illuminations in large image-shearing ESPI, two interferometers are formed. Carrier fringe patterns can be introduced by tilting reference surface a small angle. The carrier fringe patterns are demodulated after deformation of the object. Two phase maps, which include out-of-plane and in-plane displacement, can be obtained by using Fourier transform. Then out-of-plane displacement can be easily separated from in-plane displacement by simple operation between two unwrapped phase distributions. The principle of spatial carrier frequency modulation in large image-shearing ESPI is discussed. A typical three-point-bending experiment is completed. Experimental results are offered. The results show that the method offers high visibility of carrier fringes. And the system presented does not need a special beam as a reference light and has simple optical setup.     

Monitoring/measurement of out-of-plane vibrations using shearing interferometry and interferometric grating

In this paper, an application of shear plate interferometry combined with moiré readout to monitor/measure out-of-plane vibrations is presented. Moiré fringes are produced between the fringe pattern from the shear plate and interferometric grating recorded by photographing the interference pattern generated from the shear plate. It is demonstrated that the method can be used to study periodic and non-periodic vibrations.     

Estimation of the 2D measurement error introduced by in-plane and out-of-plane electronic speckle pattern interferometry instruments

Optical interferometric metrology techniques are being increasingly used in industry. These techniques assure a greater accuracy in measuring displacements caused by deformations. One such technique, electronic speckle pattern interferometry (ESPI), has been used successfully to measure in-plane and out-of-plane deformations. The usual model describing ESPI instruments behaviour is only valid in or near the centre of the illuminated surface. In general, this model is used as such for all the points on the surface creating thus an approximate figure of the reality. This study has led to an improved 3D vectorial model, allowing us to assess qualitatively and quantitatively what is actually measured throughout all the inspected surface. Calculations with practical parameters taken from real ESPI instruments designed in the Joint Research Centre of Ispra (Italy) were carried out. The results showing three-dimensional diagrams of the measurement errors are presented and discussed.     

Volume-grating phase-shifting digital speckle pattern interferometry used for measurement of out-of-plane displacement field

A new digital speckle pattern interferometry, called volume-grating phase-shifting digital speckle pattern interferometry, is discussed in this paper. The out-of-plane displacement field of a bent plate can be quantitatively measured using volume-grating phase-shifting digital speckle pattern interferometry proposed in this paper. Theoretical and experimental results, as well as absolute errors, are given.     

Measurement of out-of-plane static and dynamic deformations by processing digital speckle pattern interferometry fringes using wavelet transform

In this paper, we are presenting measurement of static and dynamic deformations in rectangular plate fixed at one end using digital speckle pattern interferometry (DSPI). To improve the measurement accuracy, we have developed a new filtering scheme based on combination of average/median filtering and Symlet wavelet filtering which enhances the signal-to-noise ratio (SNR) in the speckle interferogram obtained from DSPI. Experimental results show that our filtering scheme is quite effective in improving SNR of the speckle interferogram. The measurements by DSPI and calculations from beam theory in the case of out-of-plane static deformation and the measurements by DSPI and accelerometer in the case of dynamic deformation are in good agreement.     

Measuring small wavelength differences by heterodyne interferometry and optical activity of chiral crystal

The optical activity of a chiral crystal and common-path heterodyne interferometry are used in a simple measurement technique that was developed to measure small wavelength differences. When circularly polarized heterodyne light passes through a chiral crystal, the plane of polarization rotates. The phase difference between the right- and left-circular lights is directly proportional to the angle of rotation. The rotation angle depends strongly on the wavelength. The phase difference can be accurately detected and substituted into specially derived equations to estimate wavelength variations. The feasibility of this method was demonstrated and the wavelength sensitivity was about 0.00812 nm. This method provides the advantages of a simple structure, ease of operations, a large wavelength measurement range and high sensitivity.     

Influence of in-plane displacement and strain components on slope fringe distributions in double-aperture speckle wedge-shearing interferometry

The influence of in-plane displacement and strain components on slope (first-order derivative of out-of-plane displacement component) fringe distributions in double-aperture speckle wedge-shearing interferometry is discussed in detail. The research results show that only the in-plane displacement component parallel to the centre line of double apertures has an influence on the slope fringe distributions. It is also shown that the in-plane strain components have no influence on the slope fringe distributions when utilising normal illumination and an axisymmetric system. A theoretical analysis and an experimental demonstration are given. The experimental results are in good agreement with the quantitative analysis.     

利用光切方法测量微结构的三维微运动

微结构动态特性的测试方法对研发可靠的、能市场化的微机电系统(MEMS)是必需的。开发出了一种测试系统,能使微结构的三维运动可视化。系统包括:利用光学显微镜来实现微结构的放大,并将图像投影到CCD摄像机上;利用光切方法来获取一系列图像,以此来表征微结构的三维运动;利用频闪照明来冻结微结构的高速运动。通过研究微加工水平谐振器在激励条件下的三维运动,论证了系统的功能。     

利用Mirau显微干涉仪测量微器件的纳米级运动

描述了一种用于微机电系统（MEMS）纳米级微运动测量的Mirau显微干涉系统.该系统利用商业化的Mirau显微干涉仪，它直接安装在光学显微镜上，用于测量一个表面微加工水平谐振器的三维运动.面内运动取决于亮场在最佳焦平面处的图像，而离面运动则取决于频闪得到的干涉图像，该图像在物镜纳米定位器的8个不同位置处得到.实验结果表明了系统进行面内和离面运动测量的纳米级分辨力.     

利用激光全息干涉测量梁的微小位移

全息干涉测量利用二次曝光记录物体在不同载荷状态下的相对位移场.通过在干板上记录和比较不同状态产生的光波的干涉,可以得到在不同载荷时干涉条纹随物体位移的变化情况,实现对物体微小变形、微小位移量的测量.本文利用激光全息干涉技术测量了金属梁的微小位移量,计算得到金属梁的弹性模量和挠度.     

Measuring thickness change of transparent plate by electronic speckle pattern interferometry and digital image correlation

The thickness change of transparent plates was measured by electronic speckle pattern interferometry (ESPI) method and digital image correlation (DIC) method. An out-of-plane ESPI system was developed based on the Michelson interferometer, and a new thickness measurement method was designed, which is on the basis of Snell's law of refraction and DIC. The main principles and experimental procedures of these two methods were presented. The thickness change of polymethyl specimens under uniaxial tensile loading were measured by the optical techniques and compared with each other. The results reveal that the data obtained with DIC method achieve better linearity than ESPI.     

Sensitivity and optimization in the determination of deformations by holographic interferometry

The use of a fringe-counting holographic interferometric technique for measuring small superficial displacements can present difficulties in determining the measurement inaccuracy. A useful general method is given here for the analysis of errors in displacement measurements. The optimum number and type of observation directions are determined and correspond to counting in the four semi-diagonals of the holographic plate. The technique, as applied to skull experiments, makes it possible to measure directly displacements of up to 20 μm, in the object plane parallel to the holographic plate. The associated errors range from 0.1–0.3 μm, for a counting inaccuracy of of a fringe and increments of traction of 100 g to 1 kg of force.     

Real time addition or subtraction of two images by vector wave interferometry

The present article reports a new optical method for real time addition or subtraction of two photographic images. Two transparencies which are placed in the two arms of a Mach-Zehnder interferometer with two orthogonal polarizers are subsequently added or subtracted by rotating an analyser inserted in the output beam. A linear combination of the amplitudes of the two images can also be observed for different orientations of the transmission axis of the analyser. Some experimental results are presented.     

Comparison of two filament lamps by difference hologram interferometry

Total bulb fill pressure and density changes inside incandescent lamps can be studied by holographic interferometry. The main drawback stems from the fact that such techniques only provide information concerning the integral refractive index changes in response to a given electrical load. Difference hologram interferometry results in a direct comparison of any one of the large volume production lamps with a master lamp. A short discussion of the technique is presented and its experimental application is described where the difference interferogram is evaluated automatically.     

高双折射光纤中模式耦合空间分布的干涉测量法

本文应用干涉技术测量高双折射偏振保持光纤中模式耦合点的空间分布，测量系统由采用宽带来半导体激光器作为光源的调制迈克尔逊干涉仪组成，通过光程扫描方法探测沿高双折射光纤分布的模式的耦合点。     

Measurement of modal damping by electronic speckle shearing interferometry

A time-average electronic speckle shearing interferometer (ESSI) has been used for modal damping measurement. This is effected by a new fringe enhancement technique. The damping factor of a cantilever measured by using this technique agrees well with the value measured by using the accelerometer method. The study shows that time-average speckle interferometry can be used as a convenient tool for modal damping measurement.