Determination of characteristic parameters in integrated photoelasticity by phase-shifting technique

In this paper a new whole field technique for determination of characteristic parameters in integrated photoelasticity using phase-shifting methodology is proposed. Appropriate optical arrangements necessary for this are presented and the intensity equations are obtained by Jones calculus. The new methodology is verified experimentally for the problem of a circular disk under diametral compression viewed in oblique incidence.     

Multi-wavelength phase-shifting interferometry for micro-structures measurement based on color image processing in white light interference

Conventional multi-wavelength phase-shifting interferometry utilizes two or three monochromatic light sources, such as lasers, to realize the measurement of the surface topography with large discontinuity. In this paper, the white light source, with a single-chip CCD color camera, is used to accomplish multi-wavelength phase-shifting interferometry. In addition, we propose an algorithm which combines white light phase-shifting algorithm, equivalent wavelength method and fringe order method to achieve measuring and calibrating the micro-structures ranging from nanometer scale to micrometer scale. Finally, the proposed method is validated by a traceable step height standard.     

Phase shifting photoelasticity in white light

The availability of image acquisition systems has led to the development of digital photoelasticity both in monochromatic and white light. In particular white light has been used mainly with the following methods: Spectral Content Analysis, RGB photoelasticity and phase shifting photoelasticity. Phase shifting photoelasticity in the colour domain has been used effectively for the determination of the isoclinic parameter in order to reduce the influence of the isochromatic fringes. The method has been also proposed for the determination of the isochromatic fringe order. This paper concerns the general characteristics of phase shifting photoelasticity in the colour domain. Special attention is drawn towards the influence of spectral content of the light source, the spectral response of the colour camera filters, the dispersion of the birefringence and the error of quarter wave plates.     

Digitally whole-field analysis of isoclinic parameter in photoelasticity by four-step color phase-shifting technique

This paper presents a whole-field method for automatic determination of the isoclinic parameter φ in photoelasticity. The method determines φ in the true phase interval (-π/2<φ+π/2) based on the four-step color phase-shifting approach and a new unwrapping method based on simple logic operations, a binary image and a gray-scale mask. A plane polariscope with a white light source is used for capturing raw photoelastic fringe images. The theoretical validation of the method is done with the problem of a circular disk under compression. Comparisons between theoretical and experimental results are also demonstrated. The experimental confirmation for the proposed method is tested with the photoelastic model having an isotropic point(s) and/or a singular point(s). The results show the method permits the reliable isoclinic parameter to be determined in the true phase interval with almost no defects of the isochromatic parameter.     

Colour image enhancement by white light spatial filtering

Colour enhancement of transparencies with degraded colours is obtained by attenuation of the zero order component of the white light spatial spectrum. The filtering is performed in two ways, directly and sequentially, and the efficiency of the enhancement is estimated through the measurement of the colour difference for several pairs of colours of the object. The method is described in detail and some colour results are presented.     

Evaluation of yarn defects by image processing technique

Yarn defect evaluation, since they can drastically deteriorate the quality of the product, is one of the most important problems in textile industry. In this work, the yarn defects are evaluated by image processing technique. Initially, images were taken by scanner, later the obtained images were modified by using several filters. Then, the yarn defects were identified base on their geometric shape and surface area. As the results show, image processing methods is excellently reliable in evaluating number and type of yarn defects.     

Noise removal in three-fringe photoelasticity by adaptive colour difference estimation

Three-fringe photoelasticity (TFP) can give the total fringe order from a single-colour isochromatic fringe field. In TFP, the total fringe order is obtained by comparing the colour of the unknown photoelastic fringe pattern with a calibration specimen. Comparison is conventionally done by minimising the colour difference error. This leads to misidentification of fringe order in some regions. A new colour difference formula is proposed with an additional term, which ensures continuity of fringe order data over the domain. Fringe order data obtained by conventional TFP is used as base data and the new method is termed as refined TFP. To enable applicability of the technique to arbitrary geometries, a new boundary identification technique is developed. The new method is demonstrated with some example problems.     

Full-phase image encryption by two-step phase-shifting interferometry

We have proposed a full-phase image encryption method based on double random-phase encoding in Fresnel domain and pixel random permutation (PRP) technique with the use of two-step phase-shifting interferometry (PSI) we reported recently, and verified the effectiveness of this method and its robustness against occlusion and noise attacks by a series of numerical simulations. Comparing with other similar methods, this approach can decrease the number of the interferograms to be delivered from at least three needed in ordinary PSI to only two, give much better performance of image reconstruction than amplitude-based encryption, and provide much higher security level. This method is usable for both the gray-level images and binary images, and usually the latter will lead to better results.     

对用空间扩展宽谱光源再现的彩虹全息像的分析

用空间扩展宽谱光源再现的彩虹全息像时,整个光源只在一定的光谱的和空间的“有效宽度”内起作用,本文在此概念的基础上,研究了光源的光谱扩展和空间扩展在其单独作用和联合作用时对全息像的影响。发现当两者联合作用时,对像质的总影响几乎与它们单独作用时一样。给出了用宽谱空间扩展光源所再现的彩虹全息像的分辨率,从而提出了一个实用的狭缝宽度。     

A white light speckle schlieren technique

We present a simple optical system based on white light speckle technique for the visualization and semiquantitative evaluation of optical gradients. At variance with the classical Schlieren technique it can handle large observation areas without requiring large size curved mirrors.     

Enhancement of near-field phase-shifting contact lithography by immersion technique

Near-field phase-shifting contact lithography is theoretically modeled incorporating the immersion technique for improvement of photoresist features. The absorption patterns in the photoresist layer, which correspond to the resolution of features after development, are found to be localized in a more compact and uniform fashion with the immersed lithographic system than with the dry system. Therefore, the resolution and profiles of the high-aspect-ratio features can be notably enhanced by immersion lithography.     

相移法获取三维光弹特征相位差的方法

对于三维光弹模型,次主应力及其方向沿入射光连续变化,根据光学等效的原理,可以将三维光弹模型等效为一个包含线性相位延迟器和旋光器的光学模型。在集成光弹法中,对于每一个测量点,研究者必需通过实验获取三个特征参数。提出了一种用于确定集成光弹中全场特征相位差的五步相移法,给出了偏振光场中元器件的设置方法,并运用Jones算子推导出相移法得出的光强公式。最后使用斜射法对径向受压圆盘进行实验,验证了方法的有效性。     

A study of mixed mode fracture by photoelasticity and digital image analysis

In this paper, the results from two experimental methodologies, photoelasticity aided by digital image processing and precision digital image correlation, are presented for a mixed mode fracture problem. The mixed mode fracture problem was a three-point-bend edge-crack specimen which was loaded at various off-crack-line locations between the crack line and the specimen support line. The estimations of K_I and K_II from both methodologies indicate that the crack tip stress field is strongly intensified by K_I but not K_II.     

A new method for photoelastic fringe analysis from a single image using elliptically polarized white light

A new two-dimensional photoelastic method for the analysis of fringe order and the principal direction of birefringence from a single image combining an elliptically polarized white light and color image processing is demonstrated. To determine fringe order, a database-search approach based on the primary color analysis is employed. After determining fringe order, the principal direction of birefringence is obtained by solving a non-linear equation. The equation of emerging light intensity is derived and the theory of the proposed method is described. Then, the successful application of the method to photoelastic analysis is shown. It is emphasized that the proposed method can be applicable to time-varying phenomena since multiple exposures are not necessary for sufficient data acquisition for the completion of stress analysis.     

利用DIP技术测定荷质比

将数字图像处理(DIP)技术用于汞546.1nm谱线塞曼分裂横效应π谱线、σ谱线的图像处理,建立了CCD实时测量系统。通过多图像平均,图像细化,取样分析,快速方便地测量计算了电子的荷质比。结果表明,直接测量无法分辨的σ谱线可以通过数字图像处理测量;测量π谱线引起的相对误差小于1%,比直接测量法降低了近一个数量级。     

抛物面镜系统的光学图像处理

讨论了抛物面镜的变换特性;提出用一个凹抛物面反射镜组成光学图像处理系统,进行了相干光,部分相干光和白光的若干光学图像处理实验,证明了系统的可行性,并对系统的实用意义作了若干讨论.     

Atom cooling by white light

The performances of white light cooling are shortly reviewed and discussed. The velocity distributions modified by the cooling laser are calculated under different boundary conditions and a new experimental approach, which permits to obtain a sharp edge laser bandwidth, is taken into consideration. Finally, the preliminary experimental results on a sodium beam cooled by a lamp laser are reported.     

利用透射光栅寻找迈克耳孙干涉仪的白光干涉条纹

介绍了借助透射光栅调整迈克耳孙干涉仪的白光干涉条纹的方法和原理，并讨论了其中的有关现象．     

The influence of ambient illumination on colour adaptation in three fringe photoelasticity

In three fringe photoelasticity, a single colour isochromatic image is used to estimate the total fringe order by comparing the colour at each point with that of a calibration table. The generation of the calibration table is critical, and certain nuances involved therein are brought out in this paper. Ideally, the same specimen material and lighting conditions must be used for both the calibration and application experiments, which are often not possible in an industrial scenario, and colour adaptation is a simple way of suitably modifying the calibration table. Till date, only experimental analyses of the colour adaptation procedures are available in the literature; in this paper, the colour adaptation procedures are investigated from an analytical viewpoint. This study has brought out that a two-point colour adaptation scheme accounts not only for tint variation between the calibration and application specimens, but also for ambient illumination. This finding has also been experimentally verified for a benchmark problem, and thereafter extended for reflection photoelastic analyses.     

Some aspects of image processing using foams

We have explored some concepts of chaotic dynamics and wave light transport in foams. Using some experiments, we have obtained the main features of light intensity distribution through foams. We are proposing a model for this phenomenon, based on the combination of two processes: a diffusive process and another one derived from chaotic dynamics. We have presented a short outline of the chaotic dynamics involving light scattering in foams. We also have studied the existence of caustics from scattering of light from foams, with typical patterns observed in the light diffraction in transparent films. The nonlinear geometry of the foam structure was explored in order to create optical elements, such as hyperbolic prisms and filters.