Measurement of in-plane and out-of-plane displacements and strains using digital holographic moiré

Sai Siva Gorthi, Rishikesh Dilip Kulkarni, Pramod Rastogi
Taylor & Francis, 2014
Journal paper

The paper proposes a non-destructive method for simultaneous measurement of in-plane and out-of-plane displacements and strains undergone by a deformed specimen from a single moire fringe pattern obtained on the specimen in a dual beam digital holographic interferometry setup. The moire fringe pattern encodes multiple interference phases which carry the information on multidimensional deformation. The interference field is segmented in each column and is modeled as multicomponent quadratic/cubic frequency-modulated signal in each segment. Subsequently, the product form of modified cubic phase function is used for accurate estimation of phase parameters. The estimated phase parameters are further utilized for direct estimation of the unwrapped interference phases and phase derivatives. The simulation and experimental results are provided to validate the effectiveness of the proposed method.

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Sai Siva Gorthi, Rishikesh Dilip Kulkarni, Pramod Rastogi
Taylor & Francis, 2014
Journal paper

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https://infoscience.epfl.ch/record/199600?ln=en

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Simultaneous measurement of in-plane and out-of-plane displacements using pseudo-Wigner-Hough transform

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A new method based on pseudo-Wigner-Hough transform is proposed for the simultaneous measurement of the in-plane and out-of-plane displacements using digital holographic moire. Multiple interference phases corresponding to the in-plane and out-of-plane displacement components are retrieved from a single moire fringe pattern. The segmentation of the interference field allows us to approximate it with a multicomponent linear frequency modulated signal. The proposed method accurately and simultaneously estimates all the phase parameters of the signal components without the use of any signal separation techniques. Simulation and experimental results demonstrate the efficacy of the proposed method and its robustness against the variations in object beam intensity. (C) 2014 Optical Society of America

Optical Society of America2014

Estimation of displacement derivatives in digital holographic interferometry using a two-dimensional space-frequency distribution

Sai Siva Gorthi, Pramod Rastogi

The paper introduces a two-dimensional space-frequency distribution based method to directly obtain the unwrapped estimate of the phase derivative which corresponds to strain in digital holographic interferometry. In the proposed method, a two-dimensional pseudo Wigner-Ville distribution of the reconstructed interference field is evaluated and the peak of the distribution provides information about the phase derivative. The presence of a two-dimensional window provides high robustness against noise and enables simultaneous measurement of phase derivatives along both spatial directions. Simulation and experimental results are presented to demonstrate the method’s applicability for phase derivative estimation.

Optical Society of America2010

Simultaneous measurement of in-plane and out-of-plane displacement derivatives using dual-wavelength digital holographic interferometry

Sai Siva Gorthi, Pramod Rastogi

The paper introduces a method for simultaneously measuring the in-plane and out-of-plane displacement derivatives of a deformed object in digital holographic interferometry. In the proposed method, lasers of different wavelengths are used to simultaneously illuminate the object along various directions such that a unique wavelength is used for a given direction. The holograms formed by multiple reference-object beam pairs of different wavelengths are recorded by a 3-color CCD camera with red, green, and blue channels. Each channel stores the hologram related to the corresponding wavelength and hence for the specific direction. The complex reconstructed interference field is obtained for each wavelength by numerical reconstruction and digital processing of the recorded holograms before and after deformation. Subsequently, the phase derivative is estimated for a given wavelength using two-dimensional pseudo Wigner-Ville distribution and the in-plane and out-of-plane components are obtained from the estimated phase derivatives using the sensitivity vectors of the optical configuration.

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