Spectrally-resolved white-light interferometry as a profilometry tool

Phase-shifting interferometry and white-light interferometry are reliable techniques for surface analysis in which the optical path difference has to be changed by some transducer to evaluate the phase. We present here a different procedure in which optical path modulation is completely avoided. This technique is based on the spectral analysis of white-light interferograms. By means of a spectroscopic device, a non-visible interferogram is split into its monochromatic components and absolute, unambiguous values of the phase are obtained along the spectral axis. Only one interferogram is required to obtain the profile of one-dimensional surfaces with nanometric resolution.     

Interferometric 3-D displacement measurement using wavefront analysis

We propose and demonstrate a novel interferometric technique for 3-D displacement measurement. The method is based on the analysis of the phase difference distribution measured when two coherent curved wavefronts originating from different locations interfere. Both the in-plane and out-of-plane displacements are found simultaneously from a single phase difference distribution. We find that our system could measure with an accuracy better than 1.5 μm for in-plane displacements and 36 μm for out-of-plane displacements over 1 mm range. This accuracy was limited by the output lens performance. Theoretical analysis reveals that sub-micron accuracy may be possible with more careful calibration.     

The development of full field interferometric methods for fluid velocimetry

The development of full field interferometry as a velocimetry technique in experimental fluid mechanics from its inception in 1977 to the present is discussed. In 1977, holographic interferometry (HI) was applied for the first time to measure the velocity field in a liquid flow. It was not until 1998 that the first application to a gaseous flow was reported. The only kind of speckle interferometry that has been applied to measure velocity fields so far is digital speckle pattern interferometry (DSPI). It was in 1999 that DSPI was demonstrated both in a liquid and a gaseous flow.     

Using atom interferometry to search for new forces

Atom interferometry is a rapidly advancing field and this Letter proposes an experiment based on existing technology that can search for new short distance forces. With current technology it is possible to improve the sensitivity by up to a factor of 10² and near-future advances may be able to rewrite the limits for forces with ranges from 1 mm to 100 m.     

Possibility to break through limitation of measurement range in dual-wavelength digital holography

By using the beat frequency technique, the dual-wavelength digital holography(DWDH) can greatly increase the measurement range of the system. However, the beat frequency technique has a limitation in measurement range. The measurement range is not larger than a synthetic wavelength. Here, to break through this limitation, we propose a novel DWDH method based on the constrained underdetermined equations, which consists of three parts:(i) prove that the constrained underdetermined equation has a unique integer solution,(ii) design an algorithm to search for the unique integer solution,(iii) introduce a third wavelength into the DWDH system, and design a corresponding algorithm to enhance the anti-noise performance of DWDH. As far as we know, it is the first time that we have discovered that the problem of DWDH can belong in a problem of contained underdetermined equations, and it is also the first time that we have given the mathematical proof for breaking through the limitation of the measurement range. A series of results is shown to test the theory and the corresponding algorithms. More importantly, since the principle of proposed DWDH is based on basic mathematical principles, it can be further extended to various fields, such as dual-wavelength microwave imaging and dual-wavelength coherent diffraction imaging.     

A white-light interferometer using a lamp source and heterodyne detection with acousto-optic modulators

A heterodyne technique for white-light interferometer with a lamp source, which uses two acousto-optic modulators, is developed for high-sensitivity detection of weak light. By using converging input beams input into a Michelson interferometer with spherical mirrors, the spectral dependence of the modulators is canceled, and the white-light heterodyne interference fringes are generated at 200 kHz. Using a tandem interferometer, the object surface which has a low surface reflectivity of less than 10⁻⁴ was detected with a good signal-to-noise ratio.     

Wedge plate interferometry: a new dual field configuration for collimation testing

A method of deriving a dual field fringe pattern from a single wedge plate for collimation testing is presented. The proposed technique uses a wedge plate and a 90° prism retroreflector to form two interference fields. With the two sets of fringes, the technique provides twofold increase in sensitivity and has its own reference.     

一种改进的载波电子散斑干涉处理方法

提出了一种新的载波电子散斑干涉的处理方法,该方法将载波所形成的直条纹和包含物体变形信息的弯曲条纹在频域直接比较, 避免了传统载波干涉方法中的载波频率计算和由此带来的误差. 因此在准确程度和方便性方面都有明显改进. 本文在给出理论分析的同时进行了实验验证.     

Continual deformation analysis with scanning phase method and time sequence phase method in temporal speckle pattern interferometry

If a laser beam illuminates a continual deformation object surface, it will lead to a temporal speckle pattern on the observation plane. Recording this time-dependent speckle pattern the deformation of the surface of an object can be obtained. Two methods, scanning phase method (SPM) and time sequence phase method (TSPM), have been introduced for measuring the displacement caused by the deformation in temporal speckle pattern interferometry (TSPI). Their principle is that by capturing a series of speckle interference patterns related to the object deformations, the fluctuations in the intensity of the interference patterns can be obtained. Through scanning these fluctuations and estimating both the average intensity and modulation of the temporal speckle interference patterns, the phase maps for whole-field displacements are calculated. In this way one is capable of quantitatively measuring continual displacements simply using a conventional electronic speckle pattern interferometry (ESPI) system without phase shifting or a carrier. The elaboration on the new methods is given in this paper and experiments are performed to demonstrate their performance with a conventional ESPI system.     

一种用于动态测量的干涉方法

介绍一种在大型空间内精密测量三座标的干涉方法。用这种方法，能跟踪测量作空间曲线运动的目标。提出方法的主要理论和设计中必须遵循的一些原则。     

Quantitative visualization of the laser induced plume behavior using quasi-heterodyne holographic interferometry

It is very important that we understand the dynamic behaviors of the laser induced plume in welding, because the laser induced plume has considerable effects on welding efficiency and the quality of materials. Many experimental studies have been performed in order to observe the plume behaviors using a visualization method. In this paper, we describe the visualization and quantification of the laser induced plumes by pulse holographic interferometry. A pulsed Nd:YAG laser was used for the generation of laser induced plume and a Q-switched Ruby laser was employed to record the weld plume. For qualitative visualization of the laser induced plume, we used the double-exposure holographic interferometry. Then, we chose the quasi-heterodyne holographic interferometry with the dual-reference-beam and phase shifting in order to visualize the plume quantitatively. The experimental results show the visible behavior of the laser induced plume according to a change in the output power of the pulsed Nd:YAG laser and the time delay of Q-switched Ruby laser. Finally, we obtained the quantitative results by using the dual-reference-beam.     

Parallel two-step phase-shifting microscopic interferometry based on a cube beamsplitter

Parallel two-step phase-shifting interferometry for microscopy is presented, and the recording condition for generalized two-step phase-shifting interferometry is discussed. A 45° tilted cube beamsplitter enables to replicate the orthogonally linear polarized object and reference waves into two parallel beams, respectively. As a consequence, two interferograms with quadrature phase shift are obtained along the two beams, and phase reconstructed with an improved algorithm. To reconstruct the phase distribution from the two-step phase-shifting interferograms, a certain recording condition should be satisfied. However, the recording condition has not ever been discussed before. In this paper, the recording condition for the two-step phase-shifting interferometry is derived and that is: the intensity of reference wave should be no less than two times object wave intensity.     

Compact cyclic shearing interferometer: part two

A solid cyclic lateral shearing interferometer to be used with parallel beams of light for testing lenses is described. The interferometer can be modified into a polarization interferometer to be used in OTF measurement. The interferometer is compact and immune to environmental disturbance and less prone to misalignment.     

Introduction of the Impulse Response Function in Common-Path Interferometers with Fourier Plane Filters

In the present paper it will be shown how the introduction of a Fourier plane filter can create various types of common-path interferometers for measuring changes in surface tilt or curvature of an object surface. This is obtained by placing a holographic optical element in the Fourier plane of a 4-f optical system. The interferometers are analysed by using the paraxial approximation of the Huygens-Fresnel integral formalism, and the interferometer functions are given by a novel formalism using impulse response functions. Based on this technique, an interferometer for measuring dedicated changes in surface deflection is presented. This interferometer is insensitive to rigid surface rotations and displacements. The interferometer can be embedded in systems based on single point measurement of a time dependent deflection, i.e. vibrometers, as well as in full-field measurements such as electronic speckle interferometers.This paper was originally presented at the 2001 International Conference (2nd Joint OSJ-SPIE Conference) on Optical Engineering for Sensing and Nanotechnology, ICOSN 2001 which was held June 6-8, 2001 at the Pacifico-Yokohama Conference Center, Yokohama, Japan.     

A simple electronic speckle shearing interferometer

A new speckle shearing interferometer with simple setup is proposed. The interferometer can be converted easily from a speckle referenced speckle pattern interferometer into a speckle shearing interferometer and vice versa. A beamsplitter and a mirror are used to generate the shear. The amount of shear can be adjusted by simply rotating the mirror. The costs involved are low and it is particularly useful for fast inspection in non-destructive testing of structural integrity. Both the theoretical studies of the method of measurement and the experimental results are presented.     

Mechanical characterization of unplasticised polyvinylchloride thick pipes by optical methods

In this work a number of techniques (electronic speckle pattern interferometry, holographic interferometry, strain gauge and finite element method) are brought to bear in order to establish consistency in the results of strain measurement. This is necessary if optical non-destructive testing methods, such as those used here, are to gain acceptance for routine industrial use. The FE model provides a useful check. Furthermore, ESPI fringe data facilitates the extension of FE models, an approach that is of growing importance in component testing.

The use of in-plane and out-of-plane sensitive electronic speckle pattern interferometry (ESPI) for non-destructive material characterization of thick unplasticised polyvinylchloride (uPVC) pipes is presented. A test rig has been designed for stressing pipes by internal pressure. ESPI gives a complete mapping of the displacement field over the area imaged by the video camera. The results for the strain of uPVC obtained from ESPI data and from strain gauges are in good agreement. The value of Young's modulus has been obtained from the fringe data and compared with results obtained using holographic interferometry and from strain gauge measurements. The FE model also produces fringe data that is consistent with the ESPI results.     

Experimental progress in gravity measurement with an atom interferometer

Precisely determining gravity acceleration g plays an important role on both geophysics and metrology. For gravity measurements and high-precision gravitation experiments, a cold atom gravimeter with the aimed resolution of 10.⁻⁹g/Hz^1/2 (1 g=9.8 m/s²) is being built in our cave laboratory. There will be four steps for our ⁸⁷Rb atom gravimeter, Magneto-Optical Trap (MOT) for cooling and trapping atoms, initial state preparation, π/2-π-π/2 Raman laser pulse interactions with cold atoms, and the final state detection for phase measurement. About 108 atoms have been trapped by our MOT and further cooled by moving molasses, and an atomic fountain has also been observed.      

Comparison of phase recovery methods in spiral speckle pattern interferometry correlation fringes

Spiral interferometry can be used as a solution to the problem of sign ambiguity presented in the conventional speckle pattern interferometric technique when the optical phase needs to be reconstructed from a single closed fringe system. Depressions and elevations of the topography corresponding to the object deformation are distinguished by the direction of rotation of the local spiral fringe pattern. In this work, we implement and compare several methods for optical phase reconstruction by analyzing a single image composed of spiral speckle pattern interferometry correlation fringes. The implemented methods are based on contour line demodulation, center line demodulation, Spiral Phase Quadrature Transform and the 2D Riesz transform with multivector structure. Contour line and center line demodulation approaches are exclusively dedicated to images containing a fringe system with spiral structure. The others are based on the 2D Riesz transform, these being well known approaches in conventional interferometry. We examine simulated experiments and analyze some of the emerging drawbacks for solving the phase reconstruction problem by using different mean values of speckle size and background noise levels. We also discuss several numerical procedures that may well improve the efficiency and robustness of the presented numerical implementations. The performance of the implemented demodulation methods is evaluated by using a universal image quality index and therefore a quantitative comparison is also presented.     

载波相移全息干涉计量

本文报道了一项称为载波相移全息干涉计量的自动相位估算的新技术。该技术的主要特点是不同相移的条纹图案可用双曝光全息重视。这样即可用来对与时间相关的问题进行自动相位估算。