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1

Two-step blind phase-shifting interferometry based on the extreme value of interference and least-squares iterative algorithm

Xu Xiaoqing, Xie Ming, Ji Ying, Wang Yawei

Optica Applicata

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2021

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Vol. 51, nr 4

513--527

EN

To improve the measuring accuracy in two-step phase-shifting interferometry (PSI), a new approach combining the extreme value of interference (EVI) and the least-squares iterative algorithm (LSIA) is proposed to extract the phase from two-frame blind phase-shifting interferograms. This method first evaluates the phase shift between two interferograms by the EVI algorithm, and then constructs the fitted interferogram by the addition of two interferograms after filtering the corresponding background intensities, so the phase with high precision can be retrieved by combining two real interferograms and this fitted interferogram using the LSIA method. The proposed algorithm expands the flexibility of the LSIA method and has the high-precision performance compared with the existing algorithms in two-step PSI. Simulation and experiment are performed to verify the feasibility of the proposed algorithm.

2

Deflectometry for phase retrieval using a composite fringe

Liu T., Zhou C., Liu Y, Si S, Lei Z.

Optica Applicata

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2014

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Vol. 44, nr 3

451--461

EN

An improved deflectometry for wavefront measurement using a composite fringe is proposed to reduce the projection fringes and improve the accuracy. The single composite fringe contains four fringes in different directions. It goes through the tested objects and then is captured by a CCD camera. Two high frequency orthogonal fringe patterns and two single period orthogonal fringe patterns can be obtained from the composite fringe by fast Fourier transform. The unwrapping of the wrapped phase of the high frequency fringe is accomplished by the corresponding single period fringe using a heterodyne method. The wavefront is reconstructed by the integration of partial derivatives. Using only one fringe, the proposed method is more applicable to dynamic wavefront measurement. The experimental results demonstrate that the proposed method can retrieve the complex wavefronts more accurately.

3

Comparative analysis of interferogram noise filtration using wavelet transform and spin filtering algorithms

Zielinski B., Patorski K.

Opto-Electronics Review

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2010

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Vol. 18, No. 2

155-162

EN

The aim of this paper is to analyze 2D fringe pattern denoising performed by two chosen methods based on quasi-1D two-arm spin filter and 2D discrete wavelet transform (DWT) signal decomposition and thresholding. The ultimate aim of this comparison is to estimate which algorithm is better suited for high-accuracy measurements by phase shifting interferometry (PSI) with the phase step evaluation using the lattice site approach. The spin filtering method proposed by Yu et al. (1994) was designed to minimize possible fringe blur and distortion. The 2D DWT also presents such features due to a lossless nature of the signal wavelet decomposition. To compare both methods, a special 2D histogram introduced by Gutman and Weber (1998) is used to evaluate intensity errors introduced by each of the presented algorithms.

4

New Carré Equation

Almeida Magalhaes Jr P. A., Smith Neto P., Almeida Magalhaes C.

Metrology and Measurement Systems

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2010

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Vol. 17, nr 2

173-194

EN

The present work offers new equations for phase evaluation in measurements. Several phase-shifting equations with an arbitrary but constant phase-shift between captured intensity signs are proposed. The equations are similarly derived as the so called Carré equation. The idea is to develop a generalization of the Carré equation that is not restricted to four images. Errors and random noise in the images cannot be eliminated, but the uncertainty due to their effects can be reduced by increasing the number of observations. An experimental analysis of the errors of the technique was made, as well as a detailed analysis of errors of the measurement. The advantages of the proposed equation are its precision in the measures taken, speed of processing and the immunity to noise in signs and images.

5

Digital holography in flatness and crack investigation

Abdel Maaboud N. F., El-Bahrawi M. S., Abdel-Aziz F.

Metrology and Measurement Systems

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2010

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Vol. 17, nr 4

583-587

EN

Digital holography (DH) which is the technology of acquiring and processing measurement data via a CCD camera is spreading to industrial applications, finds wide employment in engineering problems of testing and investigation. In this paper, a simple digital holographic system, comprising a He-Ne laser source, CCD camera and analyzing software, is used for testing surface flatness and detecting the presence of a propagating crack on the surface plane and the effect of the crack on the neighborhood. Phase variations across the surfaces planes are extracted to represent the surface deviation from a reference plane. The analysis methods differ according to the interference fringes in the recorded holograms. Both fringe tracking and Fourier transform with phase unwrapping methods are used in the interpretation of interferometric fringe patterns.