Binarization of scanning Moiré fringe pattern

This paper describes a digital picture processing method to obtain a binary scanning moiré pattern. In this method, a bias component due to the illumination light distribution is eliminated from the scanning moiré fringe pattern to detect the zero-crossing points of the moiré profile. The binary fringe pattern is then obtained from the zero-crossing points. Experiments indicate that the method is useful for facilitating three-dimensional automatic measurement using moiré topography.     

Fracture detection by grating moiré and in-plane ESPI techniques

Optical interferometry techniques have been used for high-precision displacement measuring. Commonly, in-plane sensitive arrangements use two symmetrical collimated wavefronts for object surface illumination. However, this is a limitation when large object surface, has to be analyzed. In this case spherical illumination is needed. As a consequence of using non-collimated symmetrical dual-beams the sensitivity vector varies with the local position on the surface target. Then, this kind of illumination is also capable of detecting a lightly and systematic out-of-plane component of deformation. In this paper a theoretical analysis of the sensitivity vector components behavior is made. Each component of the sensitivity vector to minimize the required displacement component uncertainty is calculated. This study is important in the stage of planning any interferometric measurement experiment, particularly, for moiré grating interferometric technique, which has been used only in collimated illumination. By using a spherical dual-beam optical setup, the present work shows results of fracture measuring by using moiré and speckle interferometric methods. As a result, advantages and disadvantages of both techniques are discussed and an accuracy study is reported.     

Stress analysis of fibrous composites using moiré interferometry

A sensitive moiré fringe interferometer has been developed for measuring in-plane strains in engineering materials and structures. The specific advantage of this system is that it does not have to be used in an environment isolated from external vibration. As a result, it is possible to record deformation contours with a sensitivity and spatial resolution sufficient for the accurate measurement of strains even in areas of high strain gradient. The technique has been used to investigate the behaviour of a carbon fibre reinforced plastic material under fatigue loading. The changes in strain distribution have been measured as a function of the number of cycles undergone, and have been compared with theoretical predictions of the strain distribution around a hole in an orthotropic plate.     

Applications of Moiré topography measurement methods in industry

Moiré topography is able to determine the shape of an object, by pattern measuring, in a short time. Recently moiré topography has been used in various industrial fields because it has superior features that point measurement doesn't have. As it becomes popular various related techniques that fit specific needs have been developed and there is the prospect that moiré topography will become a more important measurement method and strengthen its position in the near future.

This paper explains the grid irradiation method and the grid projection method as the basis of the moiré topography measurement method and describes the existing status and prospects of utilizing moiré topography measurement in the applied fields of shape measurement, flatness measurement and detection of abnormality.     

Large-deformation analysis in microscopic area using micro-moiré methods with a focused ion beam milling grating

In this study, the focused ion beam (FIB) milling method is applied to fabricate sub-micron grating on TiNi shape memory alloy materials. With self-made FIB milling gratings, scanning electron microscope (SEM) micro-moiré and digital moiré methods are successfully used to measure large deformation of porous TiNi shape memory alloys (SMA) in uni-axial compressive tests. The principles of the SEM micro-moiré method and digital moiré method are introduced, and applied to calculate large strain. The full field deformation around shear bands can be measured precisely. During the investigation, the phenomenon of furcated moiré fringes was found, and a corresponding explanation is given in this paper. The furcated fringes are generated in the locations of combined shear bands where sudden changes of strain occur. Successful results also verify that the FIB milling gratings are suitable for micro-moiré measurement and can generate high quality moiré fringes.     

Suppression of moiré fringes due to sampling of halftone screened images

When a halftone screened image is discretely sampled by, for example, a CCD array, moiré fringes sometimes appear. These moiré fringes are caused by aliasing errors due to the improper sampling rate. To suppress these fringes, a dual sampling method is proposed. In this method, halftone screened images are sampled twice with different sampling rates, and the selection of proper frequency components less suffering from aliasing errors can effectively suppress moiré fringes.     

Moiré deflectometry—ray tracing interferometry

A method for ray deflection mapping, moiré deflectometry, which is fully compatible with interferometry, is described and demonstrated by numerous examples, including testing of optical components, visualization of flow, study of transient phenomena, and modulation transfer function analysis. Unlike interferometry, moiré deflectometry is a pure ray tracing technique and, therefore, the analysis of three- dimensional objects is greatly simplified. Although the ray tracing approach to optical systems is much older than wave theory, moiré deflectometry seems to be the first attempt to apply ray tracing methods systematically to optical metrology. Moiré deflectometry is fully quantitative, interferometry-compatible in accuracy and has the additional advantage of tunable sensitivity.     

Absolute and comparative measurements of three-dimensional shape by phase measuring moiré topography

We describe a phase-measuring version of projection moiré topography which allows fully automatic on-line analysis of moiré fringe contour patterns. The technique can be used for both absolute and comparative measurements of surface form and an example of each type of measurement is presented.     

Theoretical assessment of optical resolution enhancement and background fluorescence reduction by three-dimensional nonlinear structured illumination microscopy using stimulated emission depletion

Three-dimensional structured illumination microscopy (SIM) enlarges frequency cutoff laterally and axially by a factor of two, compared with conventional microscopy. However, its optical resolution is still fundamentally limited. It is necessary to introduce nonlinearity to enlarge frequency cutoff further. We propose three-dimensional nonlinear structured illumination microscopy based on stimulated emission depletion (STED) effect, which has a structured excitation pattern and a structured STED pattern, and both three-dimensional illumination patterns have the same lateral pitch and orientation. Theoretical analysis showed that nonlinearity induced by STED effect, which causes harmonics and contributes to enlarging frequency cutoff, depends on the phase difference between two structured illuminations and that the phase difference of π is the most efficient to increase nonlinearity. We also found that undesirable background fluorescence, which degenerates the contrast of structured pattern and limits the ability of SIM, can be reduced by our method. These results revealed that optical resolution improvement and background fluorescence reduction would be compatible. The feasibility study showed that our method will be realized with commercially available laser, having 3.5 times larger frequency cutoff compared with conventional microscopy.     

Fourier transform moiré tomography for high-sensitivity mapping asymmetric 3-D temperature field

Fourier transform evaluation for moiré deflectogram is proposed to automatically map the temperature field. The moiré deflectogram is generated by conventional deflectometer and is analyzed by means of Fourier transform algorithm. The convolution backprojection algorithm is used for the optical tomography. Asymmetric 3-D gas temperature distribution for a given layer is reconstructed.     

Nonparaxial method for computing the gradient field of a wavefront using moiré deflectometry

A nonparaxial method in moiré deflectometry to obtain the gradient field of a wavefront under test is proposed. This method uses only two deflectograms without any information about the phase object. As a result, director cosines of the gradient field are computed from moiré fringe deviations on both deflectograms without ambiguities. The method is proved by using a synthetic wavefront simulation.     

A moiré system for producing numerical data of the profile of a turbine blade using a computer and video store

A new technique has been devised for coding and analysing moiré contours. It uses a video frame store in place of the more usual photographic reference grid, and a small microcomputer to automate fringe detection. The system is based on using a television camera to view a sample, the complete technique being developed primarily as an industrial tool for quality control, or as feedback sensor in flexible manufacturing.     

Deformation measurement using high resolution Moiré photography

By installing a slotted mask inside the lens of a 35 mm camera the response can be tuned to resolve 300 lines/mm. The camera is used to record changes in fine grid patterns applied to engineering structures and by analysing the processed negatives in a spatial filtering system, moiré fringe maps are generated representing in detail the separate x and y displacements that have occured. Measurements have been obtained from materials ranging from concrete to soft plastics and a variety of patterns is described for treating most surfaces.     

Optical modulation and digital demodulation of an in-plane moiré carrier

A rotational mismatch of gratings is used to generate a fringe carrier of an in-plane moiré pattern so that specimen deformation shows itself in the form of modulation of the carrier frequency. As both the unmodulated and modulated carriers are the patterns without fringe-loop or fringe-connection, they are automatically numbered with monotonical increasing orders by a digital image processing system without any ambiguity. The orders at every pixel of the image are determined by interpolation of the orders of the tracked fringes to establish two grey image files, from the difference of which, the orders of the in-plane displacement moiré are displayed with grey-level variation.     

Crystallography and defects in the epitaxial growth of titanium on MICA

Experiments are described which use bend contour patterns to precisely control the orientation of a buckled mica substrate with an epitaxial layer of titanium. The contours may be indexed with ease and mica contours can be distinguished from titanium contours. Where the mica and titanium contours are almost exactly superimposed moiré fringes can be observed and a weak beam dark field investigation has been made in such regions to look for interfacial dislocation networks.     

On the determination of elastic residual strain fields in rail wheels using moiré interferometry

Moiré interferometry was used to determine the residual strain fields in a rail wheel. Hoop, radial, and shear displacement fields were determined in a whole field manner using a novel four-beam moiré interferometer. Diffraction gratings of 150 lines/mm were employed on the specimen surface. A system of data interpolation utilizing a simple control sample scheme was developed for field environments where sample loading occurs away from the optical device. Agreement was found between the moiré technique and physical measurements of wheel contraction during sectioning. Marginal agreement was found with strain gage measurements.     

Measurement of nonlinear refraction of dyes doped liquid crystal using moiré deflectometry

Recently the nonlinear effects of the azo-dye doped liquid crystals have attracted much interest. In this paper the nonlinear refractive indices, n₂, of two dyes (Sudan Black B, Sudan III) doped nematic liquid crystal were measured at low laser powers using moiré deflectometry technique. The results show when a nonlinear sample is placed in moiré deflectometry setup, the moiré fringe patterns will rotate around the beam center because of self-focusing effect in the sample. By measuring this rotation, the magnitude and the sign of nonlinear refractive index were calculated. The n₂ values for Sudan black B is larger than Sudan III, because of some differences in molecular structure and molecular polarization.     

Talbot interferometry with an adaptive light intensity compensator

Talbot interferometry with a larger applicable scope has been investigated based on the intensity amplification method to weak moiré fringes by using photorefractive crystal as a light amplifier. It not only has function of conventional Talbot interferometry, but also is suitable for situations such as weak incident beam and detected object with strong absorption. The investigation indicates that the method or technique is feasible and the results of theoretical analysis are verified by experiments. Based on this investigation, Talbot interferometry with an adaptive light intensity compensator is proposed and some merits and demerits of the technique have briefly been discussed.     

Structured Illumination Chip Based on Integrated Optics

A compact structured illumination chip based on integrated optics is proposed and fabricated on a silicon-oninsulator platform.Based on the simulation of Gaussian beam interference,we adopt a chirped diffraction grating to achieve a specific interference pattern.The experimental results match well with the simulations.The portability and flexibility of the structured illumination chip can be increased greatly through horizontal encapsulation.High levels of integration,compared with the conventional structured illumination approach,make this chip very compact,with a footprint of only around 1 mm~2.The chip has no optical lenses and can be easily combined with a microfluidic system.These properties would make the chip very suitable for portable 3D scanner and compact super-resolution microscopy applications.     

Delamination and damage studies of composite materials using phase-shifting interferometry

Composite materials offer a unique advantage over conventional engineering materials in that structural properties can be tailored to suit specific applications. However, the inherent anisotropy and the discrete layer-by-layer fabrication method of composite materials lead to mechanical behavior and failure characteristics that are quite different from those of homogeneous materials. Consequently, failure modes such as delamination in polymer matrix composites and matrix cracking and damage in ceramic matrix materials prohibit these materials from being used in conventional engineering structures, as well as making their characterization in the laboratory difficult. In this paper, an experimental photomechanics technique called phase-shifting moiré interferometry is described. This technique is capable of providing analysts and designers (both material and structural) with detailed displacement and strain fields near discontinuities in these materials. The technique allows high resolution measurements of in-plane surface displacements to be made without introducing global smoothing errors, thus preserving the integrity of data near cracks, discontinuities and material interfaces. In this paper, the advantages of phase-shifting moiré interferometry will be illustrated through several problems involving composite materials.