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.     

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.     

Moiré methods in interferometry

The applications of moiré methods to optical interferometry are reviewed. They are used for instrumental error subtraction, reduction of spatial frequency of interferogram fringes, increase of sensitivity and the range of applications of interferometric methods, and various information processing operations. The cases of the reference beam and shear type interferometry are treated separately.     

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.     

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.     

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.     

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.     

Assessment of the quality of reedbeds using holomicroscopic moiré

Holographic interferometry is proposed to detect the change in the mechanical responses of reed stems growing in eutrophic, as compared with those in healthy, water bodies. The detection of the difference in behaviour could be a sensitive way to index the degree of eutrophication. An interferometric method based on holomicroscopic moiré is developed and preliminary results obtained are presented.     

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.     

Study of the multilayer PCB CTEs by moiré interferometry

Microelectronics packaging has been developing rapidly due to the demands for faster, lighter and smaller products. Printed circuit boards (PCBs) provide mechanical support and electrical interconnection for electronic devices. Many types of composite PCBs have been developed to meet various needs. Recent trends in reliability analysis of PCBs have involved development of the structural integrity models for predicting lifetime under thermal environmental exposure; however the theoretical models need verification by the experiment.

The objective of the current work is the development of an optical system and testing procedure for evaluation of the thermal deformation of PCBs in the wide temperature range. Due to the special requirements of the specimen and test condition, the existing technologies and setups were updated and modified. The discussions on optical methods, thermal loading chambers, and image data processing are presented. The proposed technique and specially designed test bench were employed successfully to measure the thermal deformations of PCB in the −40°C to +160°C temperature range. The video-based moiré interferometry was used for generating, capturing and analysis of the fringe patterns. The obtained information yields the needed coefficients of thermal expansion (CTE) for tested PCBs.     

Determining the micro-optical element surfaces profiles using transmission deflectometry with liquids

We propose a method for simultaneously measuring the front and back surface profiles of transparent optical components. The proposed method combines dual wavelength transmission deflectometry with liquids to record distorted phases at different wavelengths, and then numerically reconstructs the three-dimensional phase information to image the front and back surfaces of the lens. We propose a theoretical model to determine the surface information, and the imaging of achromatic lenses is experimentally demonstrated. Unlike conventional transmission deflectometry, our proposed method supports direct observation of the front and back surface profiles of the optical elements. Compared with other techniques such as interferometry, the proposed setup is simpler to align, has lower cost, and does not require coherent illumination. The proposed method can be applied to normal transmission deflectometry for determining the three-dimensional surface profiles of optical components.     

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.     

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.     

Finite fringe moiré deflectometry for the measurement of radius of curvature: an alternative approach

Moiré deflectometry, based on infinite fringe detection, is a sensitive and advantageous method for the precise measurement of optical parameters. An alternative approach, based on accurate finite-fringe detection moiré deflectometry, is described for the measurement of radius of curvature. An error estimation of the method, supported by experimental verification, is also presented. Extension of the method for the measurement of a long radius of curvature has also been suggested.     

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.     

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.     

Micromechanical thermal deformation analysis of unidirectional boron/aluminum metal-matrix composite

An experiment was conducted to document thermal deformation of a unidirectionally reinforced boron/aluminum metal-matrix composite. The specimen was subject to an isothermal loading of ΔT = − 100 °C and the deformation on a free surface perpendicular to the fibers was measured by microscopic moiré interferometry. The high sensitivity and spatial resolution made it possible to elucidate the micromechanical behavior of the specimen at the fiber level. Multiplied moiré fringe patterns with a contour interval of 35 nm/fringe contour were obtained for a hexagonal array of fibers and a square array of fibers. The stress-induced strains were determined from the fringe patterns by subtracting the free thermal contraction strains. The results revealed a free surface effect and showed asymmetrical and irregular strain distributions inherent in real (non-idealized) composite materials.     

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.     

Model-based adaptive non-null interferometry for freeform surface metrology

A model-based adaptive non-null interferometry(MANI) is proposed for steep optical freeform surfaces in situ testing. The deformable mirror(DM) affording the flexible compensation is monitored with the beam in the interferometer by a wavefront sensor. The residual wavefront aberration in the non-null interferogram is eliminated by the multi-configuration ray tracing algorithm based on the system model, especially the DM surface model. The final figure error can be extracted together with the surface misalignment aberration correction.Experiments proving the feasibility of the MANI are shown.     

Adaptation of video moiré techniques to undersea mapping and surface shape determination

Fixed and variable resolution video moiré techniques have been used to project structured illumination in a model undersea environment and a prototype system has been developed which generates equal depth contours of undersea objects and has applications in sizing, orientation and ranging. An advantage of this system is that the entire field is continously illuminated, and the moiré contours and images are formed at video rates. The spatial frequency of the structured illumination can be continously varied, providing optimal contours for a variety of object sizes. The data can be easily interpreted by eye or processed by computer to obtain surface shape, range and orientation of a known structure.