Fringe contrast-based 3D profilometry using fringe projection

Quality-guided algorithm is a widely used method in phase unwrapping. This paper shows an accurate quality map based on fringe contrast for 3D shape measurement. Phase-shifted fringe patterns are projected onto an object surface by a programmable liquid crystal projector and recorded by a CCD camera. A wrapped phase map and a fringe contrast map are extracted from the deformed fringe patterns by the phase-shifting technique. Guided by the contrast map, the quality-guided unwrapping algorithm minimizes unwanted shadow and non-uniform surface reflectance effects and is able to retrieve a correct surface profile. Validity of the proposed method is tested on a fish model and a cutting tool specimen.     

Measurement of the thickness profile of a transparent thin film deposited upon a pattern structure with an acousto-optic tunablefilter

A simultaneous volumetric thickness-profile measurement method based on an acousto-optic tunable filter for transparent film deposited upon pattern structures is described. The nondestructive thickness profilometer prevents the destruction of samples such as one encounters in using a scanning-electron microscope and provides good accuracy. The information on the volumetric thickness profile is obtained through least-squares fitting with a phase model, ?(model)(k)=2kh+? (k, d)+(offset) , which has three unknowns: surface profile h, thickness d, and an indeterminate initial phase offset. Accurate phase information in the spectral domain can be obtained by introduction of the concept of spectral carrier frequency. Experimental results for a metal patterned sample show that the volumetric thickness profile can be determined within an error range of ~10 nm .     

Complex-amplitude-based phase unwrapping method for digital holographic microscopy

A complex-amplitude-based phase unwrapping approach for digital holographic microscopy is proposed in this paper. A quality map is derived directly from the reconstructed complex amplitude distribution of object wave to evaluate noise influence and phase reliability in the wrapped phase image. Quality-guided phase unwrapping algorithm is then implemented with the quality map to retrieve continuous phase profile. Unwrapping errors caused by unreliable phase data are successfully suppressed. The effectiveness of this method is demonstrated with simulation and experimental results.     

Microscopic TV holography for MEMS deflection and 3-D surface profile characterization

Recent industrial demands for greater product quality in the fields of microelements and micro-electro-mechanical systems (MEMS) generate new challenges for metrology. The fast-growing MEMS industry requires a robust non-destructive quantitative measurement system for the characterization of their performance, reliability and integrity. A microscopic TV holographic system using a long working distance microscope with an extended zoom range has been developed for microelements and MEMS deformation and 3-D surface profile analysis. The system is capable of evaluating both rough and smooth surfaces. Noisy wrapped phase map is a usual problem in speckle interferometry. We have compared several phase-shifting algorithms for evaluation of speckle phase for their usefulness in generating less-noisy phase maps. The experimental results on a MEMS pressure sensor for out-of-plane deflection and 3-D surface profile analysis are presented.     

Shape measurement by multi-illumination method in digital holographic interferometry

In this paper, temporal phase unwrapping and short time Fourier transform (STFT) are proposed for shape measurement of an object with height steps by digital holographic interferometry (DHI). A series of digital holograms is recorded with a high-speed CCD camera using a multi-illumination method. Each pixel is processed along the time axis independently of other pixels. Two novel methods are proposed to process the wrapped phase maps: the first method is based on complex phasor (CP) and temporal phase unwrapping, and the second method is based on CP and STFT. In the STFT method, continuous phase maps are obtained by integration of the exacted instantaneous frequency. The continuous phase map can characterize the profile of the object with height steps. An experiment is conducted to verify the validity of the proposed methods.     

Digital speckle interferometry for assessment of surface roughness

In this work, the principle of interferometry is used to assess the surface roughness of the machined surfaces. Interferometry produces an interference fringe pattern when two or more light waves interact with each other. It is one of the important tool for precision optical metrology and testing. Well-known advantages of the phase shifting interferometry include high measurement accuracy, rapid measurement, good result even with low contrast fringes and that the polarity of the wave front can be determined. In fringe projection techniques, a known optical fringe pattern is projected onto the surface of interest. The fringe pattern on the surface is perturbed in accordance with the profile of the test surface, thereby enabling direct derivation of surface profile.In this work, an attempt has been made to assess the surface roughness using a speckle fringe analysis method of five frame phase shift algorithm for machined surface (ground surface). As these fringes are too noisy, advanced filtering technique has been used so as to reduce noise and to get improved wrapped phase map from the phase shifted fringes. A phase unwrapping software has been developed using discrete cosine transform (DCT) to generate the three-dimensional (3-D) profiles. Finally, it is compared with R_a values measured using a mechanical stylus instrument, showing good agreement.     

A new quality map for quality-guided phase unwrapping

A new quality map for quality-guided phase unwrapping is presented. The quality map is derived from the wrapped phase map directly and can reflect phase quality accurately. It is demonstrated that the proposed quality map is a good phase-quality indicator, with which the quality-guided unwrapping algorithm can retrieve a reliable phase profile.     

一种针对彩色物体的光栅投影三维测量方法

针对传统彩色编码光栅三维轮廓术中光栅易受到物体表面彩色纹理的干扰,从而造成编码条纹颜色误判和相位误差增大这一问题,提出一种基于互补彩色光栅的三维测量方法,给出了理论分析、光栅设计原理、补偿算法与实验分析。对图像进行初步的解耦校正后,通过预先设计的光栅互补特性,依据彩色响应模型求取物体表面逐点的反射率,并对红绿蓝(RGB)三通道反射率的不平衡进行补偿,消除物体表面彩色纹理的干扰,改善光栅的正弦性。以补偿后的图像来指导彩色编码条纹的分割解码并用傅里叶变换法提取出包裹相位,依据解码结果指导相位展开,继而完成整个三维测量过程。实验证明该方法对彩色纹理的补偿准确有效,降低了彩色纹理对测量的影响。     

相移阴影莫尔条纹正交化解调技术

提出一种基于克莱姆正则化分析法的三帧自标定相移阴影莫尔三维轮廓技术.该技术首先采用移动光栅的方法获得相移条纹图,然后通过不同帧相移条纹图相减去除条纹图背景,进而结合克莱姆正交化法和最小二乘法,发展了一种相位解调方法,提取了测量相位.以五步Harlharan算法为参考,用不同算法对同一物体表面进行测量.结果表明,相对于典型的三步相移法和主量分析方法,提出的方法测量得到的相位误差最小(0.5rad),且简化了测量过程.     

Fringe projection profilometry with nonparallel illumination: a least-squares approach

Under a nonparallel illumination condition, fringe patterns projected on an object have unequal fringe spacing that would introduce a nonlinear carrier phase component. This Letter describes a nonlinear carrier removal technique based on a least-squares approach. In contrast with conventional methods, the proposed algorithm would not magnify phase measurement uncertainty, nor does it require direct estimation of system geometrical parameters. The theoretical expression of the carrier phase function on the reference is derived and expanded in a power series. The unknown coefficients in the series are determined by a least-squares method. By subtracting the calculated carrier phase function from the unwrapped phase map, the phase distribution of the object profile is obtained.     

用于动态测量的双通道光学相位测量轮廓术

提出了利用编码光两个采样值实现相位测量轮廓术的原理。设计了一种偏振分光双通道测量系统，实现了两个采样值的同时记录，因而实现了动态测量，拓展了相位测量轮廓术的应用范围。文中给出了实验结果。     

Solution of the inverse problem for a heterodyne differential microscope for a stepwise profile of a microobject

The solution of the inverse problem for a differential microscope is demonstrated experimentally by the example of an object of the step type. A method for achieving superresolution based on the expansion of the response in the coordinate representation is proposed. The main parameters of the profile (the height and the width) are determined.     

偏振相位偏移电子散斑干涉术及其应用于变形测量

本文叙述了一种用于测量漫射表面变形的使用偏振相位偏移技术的电子散斑干涉术.由于采用共光路光学相位偏移技术,因而具有较高的稳定性;用计算机图像处理可精确地获得相位图;用去包裹技术(unwrapping)可直接得到表面变形的精确数据.     

Consistency of the Surface Roughness Determined from Soft-X-Ray Reflectance and Surface Profiles Measured Using a Scanning Tunnelling Microscope: Coherence Length of the Soft X-Rays

There exists serious inconsistency between the rms surface roughness determined from the Debye-Waller factor for the soft-x-ray reflectance analysis and that measured with an optical surface profiler. We have measured the surface profile of evaporated films using a scanning tunnelling microscope, and reproduce the profile with the Fourier components whose spatial wavelength is shorter than the coherence length of the incident soft x-rays in the reflectance measurement. The rms surface roughness derived from the high-pass filtered profile agrees well with that determined using the reflectance measurement. This result explains straightforwardly the photon-energy dependence of the surface roughness estimated by the soft-x-ray reflectance method.     

Polarization behaviors of twisted carbon nanotube fibers

Polarization behaviors of carbon nanotube (CNT) fibers with different twisting were reported. Scanning electron microscope and polarized Raman spectroscopy were used to investigate the prepared samples. Results indicate that surface twisting angle affects greatly the polarization angle and I_///I_⊥ ratio of twisted CNT fibers. Raman depth profile measurements imply that the twisted fibers consist of non‐uniform CNT alignments. A simplified two‐CNT‐alignment geometric model was proposed to illuminate the experimental observations. The results suggest that polarized Raman depth profile measurement would be a very useful approach for determining the distribution of CNT alignments in CNT fibers. Copyright © 2012 John Wiley & Sons, Ltd.     

Interferometric microimaging based on geometrical spin-redirection phase

A novel scheme for an interferometric microscope with which to visualize a geometrical spin-redirection phase image that represents the local inclination of microsurface structures of an object is proposed. The observed phase depends on the state of polarization and the optical constants of the object material, which enable one to distinguish the spin-redirection phase from the conventional dynamical-phase. A preliminary experiment was performed, and the phase images obtained were found to be consistent with those predicted by computer simulation based on a theoretical model.     

Three-dimensional profile measurement of the blade based on surface structured light

As the blade must have precise size and accurate shape, three-dimensional profile measurement of the blade is very important. In this paper, three-dimensional profile measurement method of the blade based on surface structured light is proposed. A new phase unwrapping method is also proposed. This encoding method combined coding fringe pattern with the four-step phase-shifting method, the coding information is embedded into the phase, which can be used to determine fringe order for absolute phase retrieval. The encoding method is simple and easy to implement, so the phase unwrapping of the blade can be quickly perform. The experimental and simulation results show that the method can achieve a high precision, high speed and low cost three-dimensional profile measurement of the blade.     

Enhancing the phase profile and contrast of an interferogram by polarization recording in bacteriorhodopsin

Interferometry is a technique for reconstructing the profiles of phase objects. We present a novel interferometric setup for generating interferograms with doubled phase profile and enhanced contrast compared with the standard interferogram. The proposed system consists of a two-beam interferometer in which the reference and test waves are circularly polarized orthogonally to each other. They are superposed upon a bacteriorhodopsin film, creating a polarization grating that is distorted by the phase of the test object. This polarization pattern is read by a polarized He-Ne beam. We show analytically and experimentally that, when the zero diffraction order is removed, an interferogram with doubled phase profile and enhanced contrast is obtained.     

表面粗糙度测量的磁光位相调制和锁相干涉

提出了一种表面粗糙度测量的新方法，该方法采用了微分偏振干涉的原理，利用由法拉第磁光调制器所组成的调制系统对偏振干涉光路的位相进行调制，利用锁相干涉原理对位相进行探测，该方法可实现无参考面快速非接触测量，在普通实验条件下，也可保持良好的稳定恶性循环 ，实验装置即可给出表面的轮廓又可给出其它统计数据，其横向分辨率为１．２μｍ纵向为２ｎｍ。     

Phase-shifting polarization interferometry for microstructure linewidth measurement

We report on a novel procedure to measure the linewidth of steep microstructures, based on the polarization anisotropy caused by the structure edges. A liquid-crystal phase shifter and a polarizer are introduced into the imaging optics of a reflection-mode microscope. We apply the principle of phase-shifting interferometry to measure the phase and contrast of a TM-polarized image with the TE-polarized image as reference. The method provides selective edge detection because the polarization difference is localized at the structure edges.