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Author

N. Krishna Mohan

Other affiliations: Indian Institutes of Technology
Bio: N. Krishna Mohan is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Speckle pattern & Interferometry. The author has an hindex of 17, co-authored 56 publications receiving 679 citations. Previous affiliations of N. Krishna Mohan include Indian Institutes of Technology.


Papers
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Journal ArticleDOI
TL;DR: In this article, an experimental approach for surface roughness measurement based on the coherent speckle scattering pattern caused by a laser beam on the machined surfaces (grinding and milling) is presented.
Abstract: The measurement of roughness on machined surfaces is of great importance for manufacturing industries as the roughness of a surface has a considerable influence on its quality and function of products. In this paper, an experimental approach for surface roughness measurement based on the coherent speckle scattering pattern caused by a laser beam on the machined surfaces (grinding and milling) is presented. Speckle is the random pattern of bright and dark regions that is observed when a surface is illuminated with a highly or partially coherent light beam. When the illuminating beam is reflected from a surface, the optical path difference between various wavelets with different wavelength would result in interference showing up as a granular pattern of intensity termed as speckle. The properties of this speckle pattern are used for estimation/quantification of roughness parameters. For measurement of surface roughness, initially the speckle patterns formed are filtered in the spatial frequency domain. The optical technique, namely spectral speckle correlation (autocorrelation) is utilized in this work for the measurement of roughness on machined surfaces. It has been observed that the pattern formed is dependent on the roughness of the illuminated surface. For example, a rough surface (milled) shows a small central bright region with a rapid decrease in intensity towards the edges, while a smooth surface (ground) shows a large central bright region with gradually decreasing intensity towards the edges. The complete methodology and analysis for quantification/estimation of surface finish of milled and ground surfaces based on speckle images that could be implemented in practice, is presented in this paper.

95 citations

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TL;DR: In this article, a two-wavelength micro-interferometric setup for 3D surface profile characterization of smooth as well as rough micro-specimens is described. But the method cannot handle smooth profiles and step heights less than half a wavelength.

75 citations

Journal ArticleDOI
TL;DR: In this article, a white light interferometer with a colour CCD camera is discussed, where interference intensity information from the three channels of the color CCD simulating three-wavelength measurement is accessed.

53 citations

Journal ArticleDOI
TL;DR: An optical configuration is presented for simultaneous measurement of out-of-plane displacement and slope change in electronic speckle pattern interferometry.
Abstract: An optical configuration is presented for simultaneous measurement of out-of-plane displacement and slope change in electronic speckle pattern interferometry. Experimental results for a rectangular plate clamped along the edges and loaded at the center are presented.

33 citations

Journal ArticleDOI
TL;DR: In this article, 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.

30 citations


Cited by
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Journal Article
TL;DR: In this article, a fast Fourier transform method of topography and interferometry is proposed to discriminate between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour generation techniques.
Abstract: A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

3,742 citations

Journal ArticleDOI
TL;DR: A comprehensive overview of shearography is presented, describing the principle of operation, optical configurations, image processing algorithms and applications, with a focus on more recent technological advances.
Abstract: Shearography is a full-field speckle interferometric technique used to determine surface displacement derivatives. For an interferometric technique, shearography is particularly resilient to environmental disturbances and has hence become an invaluable measurement tool outside of the optics laboratory. Furthermore, the inclusion of additional measurement channels has turned shearography from a qualitative inspection tool into a system suitable for quantitative surface strain measurement. In this review article we present a comprehensive overview of the technique, describing the principle of operation, optical configurations, image processing algorithms and applications, with a focus on more recent technological advances.

213 citations

Journal ArticleDOI
TL;DR: A review of development of digital image processing techniques in tool condition monitoring is discussed, a conclusion is drawn about required systematic research in this field.
Abstract: Tool condition monitoring is gaining a parallel development with the advancement of automatic manufacturing processes in the last thirty years due to the increasing need for improvement of product quality. The advances of digital image processing techniques used in tool condition monitoring are an important research interest due to the improvement of machine vision system, computing hardware and non-tactile application. In this paper, a review of development of digital image processing techniques in tool condition monitoring is discussed and finally a conclusion is drawn about required systematic research in this field.

199 citations

Journal ArticleDOI
TL;DR: The proposed scheme can provide a real-time solution for measuring three-dimensional objects having a high abrupt height difference with moderate accuracy and can be used as a fast polarization imaging measurement tool.
Abstract: We describe what we believe to be a new digital holographic configuration that can be utilized for both single-shot, dual-wavelength, off-axis geometry and imaging polarimetry. To get the feasibility of the single-shot, dual-wavelength, off-axis geometry, a sample with a nominal step height of 1.34 μm is used. Undesirable noises that strongly affect the measurement have been suppressed successfully by using a modified flat fielding method for the dual-wavelength scheme. And also, the experiment is conducted on a nanopattern sample on the basis of a single image acquisition to show the imaging polarimetry capability. The proposed scheme can provide a real-time solution for measuring three-dimensional objects having a high abrupt height difference with moderate accuracy. Furthermore, it can be used as a fast polarization imaging measurement tool.

107 citations

Journal ArticleDOI
TL;DR: Keywords: fringe analysis Reference EPFL-ARTICLE-176959doi:10.1016/j.optlaseng.2012.04.006View record in Web of Science URL: http://www.sciencedirect.com/science/article/pii/S0143816612001182

105 citations