Determination of fringe order in white-light interference microscopy
TL;DR: The algorithm adapts to surface texture and noise level and dynamically compensates for optical aberrations, distortions, diffraction, and dispersion that would otherwise lead to incorrect fringe order.
Abstract: Combining phase and coherence information for improved precision in white-light interference microscopy requires a robust strategy for dealing with the inconsistencies between these two types of information. We correct for these inconsistencies on every measurement by direct analysis of the difference map between the coherence and the phase profiles. The algorithm adapts to surface texture and noise level and dynamically compensates for optical aberrations, distortions, diffraction, and dispersion that would otherwise lead to incorrect fringe order. The same analysis also provides the absolute height data that are essential to relational measurements between disconnected surfaces.
Citations
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TL;DR: Recent advances considered here include performance improvements, vibration robustness, full color imaging, accommodation of highly sloped surfaces, correlation to contact methods, transparent film analysis, and international standardization of calibration and specification.
Abstract: Interference microscopy plays a central role in noncontact strategies for process development and quality control, providing full 3D measurement of surface characteristics that influence the functional behavior of manufactured parts. Here I briefly review the history and principles of this important technique, then concentrate on the details of hardware, software, and applications of interference microscopy using phase-shifting and coherence scanning measurement principles. Recent advances considered here include performance improvements, vibration robustness, full color imaging, accommodation of highly sloped surfaces, correlation to contact methods, transparent film analysis, and international standardization of calibration and specification.
283 citations
TL;DR: Error separation algorithms for removing machine tool errors, which is specially required in on-machine and in-process surface metrology, are overviewed, followed by a discussion on calibration and traceability.
232 citations
TL;DR: In this article, the performance of commercial scanning white light interferometers in a range of measurement tasks was examined, and it was found that most instruments report errors when used in regions close to a discontinuity or those with a surface gradient that is large compared to the acceptance angle of the objective lens.
Abstract: This paper examines the performance of commercial scanning white light interferometers in a range of measurement tasks. A step height artefact is used to investigate the response of the instruments at a discontinuity, while gratings with sinusoidal and rectangular profiles are used to investigate the effects of surface gradient and spatial frequency. Results are compared with measurements made with tapping mode atomic force microscopy and discrepancies are discussed with reference to error mechanisms put forward in the published literature. As expected, it is found that most instruments report errors when used in regions close to a discontinuity or those with a surface gradient that is large compared to the acceptance angle of the objective lens. Amongst other findings, however, we report systematic errors that are observed when the surface gradient is considerably smaller. Although these errors are typically less than the mean wavelength, they are significant compared to the vertical resolution of the instrument and indicate that current scanning white light interferometers should be used with some caution if sub-wavelength accuracy is required.
201 citations
Cites background from "Determination of fringe order in wh..."
...More generally phase jumps of this magnitude are referred to as 2π errors and can be thought of as a misclassification of fringe order [13,14]....
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...[14] de Groot P, de Lega X C, Kramer J, Turzhitsky M 2002 Determination of fringe order in white-light interference microscopy Appl....
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Patent•
08 Mar 2004
TL;DR: In this paper, a method including comparing information derived from a scanning interferometry signal for a first surface location of a test object to information corresponding to multiple models of the test object was proposed.
Abstract: A method including comparing information derivable from a scanning interferometry signal for a first surface location of a test object to information corresponding to multiple models of the test object, wherein the multiple models are parametrized by a series of characteristics for the test object. The derivable information being compared may relate to a shape of the scanning interferometry signal for the first surface location of the test object.
173 citations
Patent•
21 Sep 2006
TL;DR: Disclosed is an interferometry analysis method that includes comparing information derivable from multiple inter-ferometry signals corresponding to different surface locations of a test object to information corresponding to multiple models of the test object, wherein the multiple models are parameterized by a series of characteristics that relate to one or more under-resolved lateral features of the object.
Abstract: Disclosed is an interferometry analysis method that includes comparing information derivable from multiple interferometry signals corresponding to different surface locations of a test object to information corresponding to multiple models of the test object, wherein the multiple models are parameterized by a series of characteristics that relate to one or more under-resolved lateral features of the test object; and outputting information about the under-resolved surface feature based on the comparison.
134 citations
References
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Book•
28 Apr 1998
TL;DR: Methods for Phase Unwrapping, Phase Data, Quality Maps, Masks, and Filters, and Minimum-Norm Methods.
Abstract: Introduction to Phase Unwrapping. Line Integrals, Residues, and 2-D Phase Unwrapping. Phase Data, Quality Maps, Masks, and Filters. Path-Following Methods. Minimum-Norm Methods. Comparisons and Conclusion. Appendices. Index.
1,575 citations
TL;DR: A three-dimensional sensor designed primarily for rough objects that supplies an accuracy that is limited only by the roughness of the object surface, which differs from conventional optical systems in which the depth accuracy is limited by the aperture.
Abstract: We introduce a three-dimensional sensor designed primarily for rough objects that supplies an accuracy that is limited only by the roughness of the object surface. This differs from conventional optical systems in which the depth accuracy is limited by the aperture. Consequently, our sensor supplies high accuracy with a small aperture, i.e., we can probe narrow crevices and holes. The sensor is based on a Michelson interferometer, with the rough object surface serving as one mirror. The small coherence length of the light source is used. While scanning the object in depth, one can detect the local occurrence of interference within the speckles emerging from the object. We call this method coherence radar.
690 citations
TL;DR: The new algorithm is shown to be near optimal in terms of computational efficiency and can be represented as a second-order nonlinear filter and in combination with a carefully designed peak detection method the algorithm exhibits exceptionally good performance on simulated interferograms.
Abstract: A compact and efficient algorithm for digital envelope detection in white light interferograms is derived from a well-known phase-shifting algorithm. The performance of the new algorithm is compared with that of other schemes currently used. Principal criteria considered are computational efficiency and accuracy in the presence of miscalibration. The new algorithm is shown to be near optimal in terms of computational efficiency and can be represented as a second-order nonlinear filter. In combination with a carefully designed peak detection method the algorithm exhibits exceptionally good performance on simulated interferograms.
559 citations
TL;DR: A correlation microscope based on the Mirau interferometer configuration using a thin silicon nitride film beam splitter is constructed, which predicts accurately both the transverse resolution at a sharp edge and the range resolution for a perfect plane reflector.
Abstract: We have constructed a correlation microscope based on the Mirau interferometer configuration using a thin silicon nitride film beam splitter. This microscope provides the amplitude and phase information for the reflected signal from a sample located on the microscope-object plane. The device is remarkably insensitive to vibrations and is self-correcting for spherical and chromatic range aberrations of the objective. An imaging theory for the correlation microscope has been derived, which predicts accurately both the transverse resolution at a sharp edge and the range resolution for a perfect plane reflector. The range resolution is slightly better than that for a scanning optical microscope using a lens with the same aperture.
491 citations
TL;DR: In this article, a scanning white-light interferometer for high-precision surface structure analysis is described, where the interferogram for each of the image points in the field of view is generated simultaneously by scanning the object in a direction perpendicular to the object surface, while recording detector data in digital memory.
Abstract: We describe a scanning white-light interferometer for high-precision surface structure analysis. Interferograms for each of the image points in the field of view of the instrument are generated simultaneously by scanning the object in a direction perpendicular to the object surface, while recording detector data in digital memory. These interferograms are then transformed into the spatial frequency domain and the surface height for each point is obtained by examination of the complex phase as a function of frequency. The final step is the creation of a complete three-dimensional image constructed from the height data and corresponding image plane coordinates. The measurement repeatability is better than 0·5 nm r.m.s. for a surface height range of 100 μm.
401 citations