Mr. Matthew Thomas Profile

Matthew Thomas

at Univ of Nottingham

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Author

Publications (4)

Proceedings Article | 1 April 2020 Presentation + Paper

Optical topography measurement of steeply-sloped surfaces beyond the specular numerical aperture limit

Matthew Thomas, Rong Su, Peter de Groot, Richard Leach

Proceedings Volume 11352, 1135207 (2020) https://doi.org/10.1117/12.2554568

KEYWORDS: Interferometers, Surface quality testing, Diffraction gratings, Scattering, Modeling, Signal to noise ratio, Spatial frequencies, 3D metrology

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SPIE Journal Paper | 25 March 2020 Open Access

Modeling of interference microscopy beyond the linear regime

Matthew Thomas, Rong Su, Nikolay Nikolaev, Jeremy Coupland, Richard Leach

OE, Vol. 59, Issue 03, 034110, (March 2020) https://doi.org/10.1117/12.10.1117/1.OE.59.3.034110

KEYWORDS: 3D modeling, Instrument modeling, Microscopy, Scattering, Optical engineering, Spatial frequencies, Objectives, Multiple scattering, Data modeling, Polarization

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Proceedings Article | 3 September 2019 Presentation + Paper

High-accuracy surface measurement through modelling of the surface transfer function in interference microscopy

Rong Su, Matthew Thomas, Mingyu Liu, Jeremy Coupland, Richard Leach

Proceedings Volume 11102, 1110205 (2019) https://doi.org/10.1117/12.2528911

KEYWORDS: 3D metrology, Spatial frequencies, Microscopy, Manufacturing, 3D modeling

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Proceedings Article | 21 June 2019 Presentation + Paper

Modelling of coherence scanning interferometry for complex surfaces based on a boundary element method

Matthew Thomas, Rong Su, Nikolay Nikolaev, Jeremy Coupland, Richard Leach

Proceedings Volume 11057, 1105713 (2019) https://doi.org/10.1117/12.2526015

KEYWORDS: 3D modeling, Scattering, Interferometry, Multiple scattering, Modeling, Phase measurement, Instrument modeling, Systems modeling, Spatial frequencies

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Coherence scanning interferometry (CSI) is a well-established technique for measuring surface topography based on the coherence envelope and phase of interference fringes. The most commonly used surface reconstruction methods, i.e. frequency domain analysis, the envelope detection method, and the correlogram correlation method, obtain the phase of the measured field for each pixel and, from this obtain the surface height, by assuming the two are directly proportional. For surfaces with minor deviations from a plane, it is straightforward to show that the scattered field’s phase is a linear function of surface height. An alternative approach known as the “foil model” gives more generally the scattered field as the result of a linear filtering process operating on a “foil” representation of the surface. This model assumes that the surface slowly varies on the optical scale and that there is no multiple scattering. However, for surfaces that are rough at the optical scale or have coherent features (e.g. vee-grooves), the effect of multiple scattering cannot be neglected and remains a problem for reconstruction methods. Linear reconstruction methods cannot provide accurate surface topographies for complex surfaces, since for such surfaces, the measurement process of CSI is fundamentally non-linear. To develop an advanced reconstruction method for CSI, an accurate model of the imaging process is required. In this paper, a boundary elements method is used as a rigorous scattering model to calculate the scattered field at a distant boundary. Then, the CSI signal is calculated by considering the image formation as back-propagation of the scattered field, combined with the reflected reference field. Through this approach, the optical response of a CSI system can be predicted rigorously for almost any arbitrary surface geometry. Future work will include a comprehensive experimental verification of this model, and development of the non-linear surface reconstruction algorithm.

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