Surface Profiling by Analysis of White-light Interferograms in the Spatial Frequency Domain
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.
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TL;DR: In this paper, the authors presented experimental data and a computational model of the cold spray solid particle impact process on a polished stainless steel substrate and showed that the impact deformation exposes clean surfaces that, under high impact pressures, result in significant bond strengths between the particle and substrate.
Abstract: This article presents experimental data and a computational model of the cold spray solid particle impact process. Copper particles impacting onto a polished stainless steel substrate were examined in this study. The high velocity impact causes significant plastic deformation of both the particle and the substrate, but no melting was observed. The plastic deformation exposes clean surfaces that, under the high impact pressures, result in significant bond strengths between the particle and substrate. Experimental measurements of the splat and crater sizes compare well with the numerical calculations. It was shown that the crater depth is significant and increases with impact velocity. However, the splat diameter is much less sensitive to the impact velocity. It was also shown that the geometric lengths of the splat and crater scale linearly with the diameter of the impacting particle. The results presented will allow a better understanding of the bonding process during cold spray.
418 citations
TL;DR: An extensive frequency-domain analysis of multiple reflection is performed to allow both the top and the bottom interfaces of a thin-film layer to be measured independently at the same time by the nonlinear least-squares technique.
Abstract: White-light scanning interferometry is increasingly used for precision profile metrology of engineering surfaces, but its current applications are limited primarily to opaque surfaces with relatively simple optical reflection behavior. A new attempt is made to extend the interferometric method to the thickness-profile measurement of transparent thin-film layers. An extensive frequency-domain analysis of multiple reflection is performed to allow both the top and the bottom interfaces of a thin-film layer to be measured independently at the same time by the nonlinear least-squares technique. This rigorous approach provides not only point-by-point thickness probing but also complete volumetric film profiles digitized in three dimensions.
301 citations
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
Cites background from "Surface Profiling by Analysis of Wh..."
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...13, where the right-hand image of color fringes shows how the superimposed signals for the constituent wavelengths result in high fringe contrast at the point where all the patterns agree in phase—the so-called stationary phase position [95]....
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15 Jan 2004-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the authors examined three thermal spraying techniques with significantly different particle temperatures and velocities, including air plasma spraying (APS), twin wire-arc spraying (TWA), and high velocity oxy-fuel (HVOF) spraying.
Abstract: Thermal spray offers a variety of sub-sets of processing approaches to produce coatings. The various processes are classified based on the thermal spray source (from low velocity combustion spray to high temperature plasma jets) and method of material injection (in the form of powder, wire or rod). However, it is this intrinsic versatility which sets-up variations in characteristics of the applied coatings. Properties of thermally sprayed coatings, including process induced residual stress, are controlled by various parameters of the spraying process. This study examines three thermal spraying techniques with significantly different particle temperatures and velocities. They are air plasma spraying (APS), twin wire-arc spraying (TWA) and high velocity oxy-fuel (HVOF) spraying. For comparison purposes the recently developed cold spray processed materials were included in the study. For each method, in-flight particle diagnostics was performed; Ni–5 wt.%Al splats and deposits were fabricated and analyzed. Porosity, elastic modulus and thermal conductivity of the deposits were evaluated and correlated to the process variables. Using indentation at different loads and analysis of the indented region, stress–strain relationships for these coatings were obtained. Surprising differences in the properties were observed and were explained based on the fundamental variations in microstructure development. Through-thickness residual stress profiles in Ni–5 wt.%Al coatings on steel substrates were determined non-destructively by neutron diffraction. The stresses range from highly tensile in the APS coating to compressive in the HVOF coating. Various stress generation mechanisms—splat quenching, peening and thermal mismatch—are discussed with respect to process parameters and material properties.
264 citations
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.
224 citations
References
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TL;DR: OCT as discussed by the authors uses low-coherence interferometry to produce a two-dimensional image of optical scattering from internal tissue microstructures in a way analogous to ultrasonic pulse-echo imaging.
Abstract: A technique called optical coherence tomography (OCT) has been developed for noninvasive cross-sectional imaging in biological systems. OCT uses low-coherence interferometry to produce a two-dimensional image of optical scattering from internal tissue microstructures in a way that is analogous to ultrasonic pulse-echo imaging. OCT has longitudinal and lateral spatial resolutions of a few micrometers and can detect reflected signals as small as approximately 10(-10) of the incident optical power. Tomographic imaging is demonstrated in vitro in the peripapillary area of the retina and in the coronary artery, two clinically relevant examples that are representative of transparent and turbid media, respectively.
11,568 citations
16 Nov 1992
TL;DR: Optical coherence tomography (OCT) has developed rapidly since its first realisation in medicine and is currently an emerging technology in the diagnosis of skin disease as mentioned in this paper, where OCT is an interferometric technique that detects reflected and backscattered light from tissue.
Abstract: Optical coherence tomography (OCT) has developed rapidly since its first realisation in medicine and is currently an emerging technology in the diagnosis of skin disease. OCT is an interferometric technique that detects reflected and backscattered light from tissue and is often described as the optical analogue to ultrasound. The inherent safety of the technology allows for in vivo use of OCT in patients. The main strength of OCT is the depth resolution. In dermatology, most OCT research has turned on non-melanoma skin cancer (NMSC) and non-invasive monitoring of morphological changes in a number of skin diseases based on pattern recognition, and studies have found good agreement between OCT images and histopathological architecture. OCT has shown high accuracy in distinguishing lesions from normal skin, which is of great importance in identifying tumour borders or residual neoplastic tissue after therapy. The OCT images provide an advantageous combination of resolution and penetration depth, but specific studies of diagnostic sensitivity and specificity in dermatology are sparse. In order to improve OCT image quality and expand the potential of OCT, technical developments are necessary. It is suggested that the technology will be of particular interest to the routine follow-up of patients undergoing non-invasive therapy of malignant or premalignant keratinocyte tumours. It is speculated that the continued technological development can propel the method to a greater level of dermatological use.
6,095 citations
TL;DR: La difference de phase entre les 2 faisceaux interferant varie de maniere connue et on fait des mesures de the distribution d'intensite a travers la pupille correspondant a au moins 3 dephasages differents.
Abstract: La difference de phase entre les 2 faisceaux interferant varie de maniere connue et on fait des mesures de la distribution d'intensite a travers la pupille correspondant a au moins 3 dephasages differents
979 citations
TL;DR: An optical evaluation technique is described that is suitable for determining the positions and magnitudes of reflection sites within miniature optical assemblies using the coherence effects exhibited by a broadband optical source and is referred to as optical coherence-domain reflectometry.
Abstract: An optical evaluation technique is described that is suitable for determining the positions and magnitudes of reflection sites within miniature optical assemblies. This method utilizes the coherence effects exhibited by a broadband optical source and is referred to as optical coherence-domain reflectometry. Background theory is given, and experimental results have demonstrated a resolution of 10 μm with an optical dynamic range of more than 100 dB.
800 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