Prof. Richard K. Leach Profile

Prof. Richard K. Leach

Professor at Univ of Nottingham

SPIE Involvement:

Author | Editor

Publications (32)

SPIE Journal Paper | 12 April 2024 Open Access

Comparison of Fourier optics-based methods for modeling coherence scanning interferometry

Helia Hooshmand, Tobias Pahl, Peter de Groot, Peter Lehmann, Athanasios Pappas, Rong Su, Richard Leach, Samanta Piano

OE, Vol. 63, Issue 04, 044102, (April 2024) https://doi.org/10.1117/12.10.1117/1.OE.63.4.044102

KEYWORDS: 3D modeling, Optical surfaces, Instrument modeling, Modeling, Equipment, Light sources and illumination, Optical engineering, Interferometry, Imaging systems, 3D metrology

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Proceedings Article | 4 October 2023 Poster + Paper

Distance measurement error sources in Fourier-based frequency sweeping interferometry using a gas cell for laser frequency sweep speed determination

M. Sosin, J. Gonzalez Cobas, M. Isa, R. Leach, H. Mainaud Durand

Proceedings Volume 12684, 126840C (2023) https://doi.org/10.1117/12.2674132

KEYWORDS: Distance measurement, Analog to digital converters, Gas cells, Laser frequency, Interferometers, Signal detection, Photodetectors, Measurement uncertainty, Interpolation

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Proceedings Article | 11 August 2023 Paper

High-accuracy robotic metrology for precise industrial manipulation tasks

Mohammed Isa, Mojtaba Khanesar, Richard Leach, David Branson, Samanta Piano

Proceedings Volume 12623, 126230C (2023) https://doi.org/10.1117/12.2673088

KEYWORDS: Accuracy assessment, Robots, Robotics, Binocular vision, Optical spheres, Metrology, Robotic systems, Interferometers, Target detection, Actuators

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Proceedings Article | 10 August 2023 Presentation + Paper

Comparison of approximate methods for modelling coherence scanning interferometry

Helia Hooshmand, Tobias Pahl, Peter de Groot, Peter Lehmann, Athanasios Pappas, Rong Su, Richard Leach, Samanta Piano

Proceedings Volume 12619, 126190R (2023) https://doi.org/10.1117/12.2673657

KEYWORDS: 3D modeling, Optical surfaces, Modeling, Equipment, Instrument modeling, Light sources and illumination, Interferometry, Imaging systems, Fourier transforms

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SPIE Journal Paper | 31 December 2022

Quantitative investigation of the validity conditions for the Beckmann–Kirchhoff scattering model

Helia Hooshmand, Mingyu Liu, Richard Leach, Samanta Piano

OE, Vol. 61, Issue 12, 124113, (December 2022) https://doi.org/10.1117/12.10.1117/1.OE.61.12.124113

KEYWORDS: Light scattering, Optical surfaces, Scattering, 3D modeling, Optical engineering, Multiple scattering, Modeling, Data modeling, Polarization, Confocal microscopy

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Approximate and rigorous methods are widely used to model light scattering from a surface. The boundary element method (BEM) is a rigorous model that accounts for polarization and multiple scattering effects. BEM is suitable to model the scattered light from surfaces with complex geometries containing overhangs and re-entrant features. The Beckmann–Kirchhoff (BK) scattering model, which is an approximate model, can be used to predict the scattering behavior of slowly varying surfaces. Although the approximate BK model cannot be applied to complex surface geometries that give rise to multiple scattering effects, it has been used to model the scattered field due to its fast and simple implementation. While many of the approximate models are restricted to surface features with relatively small height variations (typically less than half the wavelength of the incident light), the BK model can predict light scattering from surfaces with large height variations, as long as the surfaces are locally flat with small curvatures. Thus far, attempts have been made to determine the validity conditions for the BK model. The primary validity condition is that the radius of curvature of any surface irregularity should be significantly greater than the wavelength of the light. However, to have the most accurate results for the BK model, quantifying the validity conditions is critical. This work aims to quantify the validity conditions of the BK model according to different surface specifications, e.g., slope angles (SA) and curvatures. For this purpose, the scattered fields from various sinusoidal and combinations of sinusoidal profiles are simulated using the BEM and the BK models and their differences are compared. The result shows that the BK model fails when there are high SA ( ⪆ 38 deg) and small radii of curvature ( ⪅ 10 λ) within a sinusoidal profile. Moreover, it is shown that for a combination of sinusoidal profiles the BK model is valid for profiles with a high maximum slope angle value ( ⪆ 38 deg) if the average of positive SA is low ( ⪅ 5 deg).

Proceedings Article | 3 October 2022 Paper

Quantifying the validity conditions of the Beckmann-Kirchhoff scattering model

Helia Hooshmand, Mingyu Liu, Richard Leach, Samanta Piano

Proceedings Volume 12221, 122210W (2022) https://doi.org/10.1117/12.2639003

KEYWORDS: Scattering, Light scattering, Multiple scattering, Modeling, Data modeling, 3D modeling, Polarization, Microscopy, 3D metrology

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Proceedings Article | 20 May 2022 Presentation + Paper

Measurement of laser-based powder bed fusion surfaces using light scattering and one-class support vector machines

Mingyu Liu, Nicola Senin, Richard Leach

Proceedings Volume 12137, 1213706 (2022) https://doi.org/10.1117/12.2621172

KEYWORDS: Laser scattering, Image processing, Scattering, Light scattering, Principal component analysis, Manufacturing, Cameras, Machine learning, Data modeling

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SPIE Journal Paper | 18 October 2021 Open Access

Modeling of coherence scanning interferometry using classical Fourier optics

Peter de Groot, Xavier Colonna de Lega, Rong Su, Jeremy Coupland, Richard Leach

OE, Vol. 60, Issue 10, 104106, (October 2021) https://doi.org/10.1117/12.10.1117/1.OE.60.10.104106

KEYWORDS: 3D modeling, Interferometry, Fourier optics, Instrument modeling, Optical engineering, Light sources, 3D metrology, Signal detection, Imaging systems, Spatial frequencies

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Proceedings Article | 5 August 2021 Presentation + Paper

Fourier optics modelling of coherence scanning interferometers

Peter de Groot, Xavier Colonna de Lega, Rong Su, Jeremy Coupland, Richard Leach

Proceedings Volume 11817, 118170M (2021) https://doi.org/10.1117/12.2595668

KEYWORDS: 3D modeling, Interferometry, Fourier optics, Instrument modeling, Objectives, Light sources, Microscopes, Diffraction, Spatial frequencies, Interferometers

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Proceedings Article | 20 June 2021 Presentation + Paper

Intelligent quality monitoring for additive manufactured surfaces by machine learning and light scattering

Mingyu Liu, Nicola Senin, Richard Leach

Proceedings Volume 11782, 1178206 (2021) https://doi.org/10.1117/12.2592554

KEYWORDS: Machine learning, Additive manufacturing, Data modeling, Light scattering, Data acquisition, Scattering, Neural networks, 3D modeling, Sensors, Metals

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Proceedings Article | 20 June 2021 Presentation + Paper

Evaluating and propagating uncertainty in digital fringe projection systems

George Gayton, Mohammad Isa, Rong Su, Richard Leach

Proceedings Volume 11782, 117821C (2021) https://doi.org/10.1117/12.2592426

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Proceedings Article | 20 June 2021 Presentation

Virtual coherence scanning interferometer for surface measurement

Rong Su, Richard Leach

Proceedings Volume 11782, 117820L (2021) https://doi.org/10.1117/12.2592255

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Proceedings Article | 7 April 2020 Presentation + Paper

Cascaded machine learning model for reconstruction of surface topography from light scattering

Mingyu Liu, Nicola Senin, Rong Su, Richard Leach

Proceedings Volume 11352, 113520Q (2020) https://doi.org/10.1117/12.2555035

KEYWORDS: Machine learning, Light scattering, Scattering, Neural networks, Computer simulations

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Light scattering methods are promising for in-process surface measurement. Many researchers have investigated light scattering methods for evaluating surface texture. Researchers working on scatterometry have developed methods to derive surface texture parameters by solving the inverse scattering problem. However, most of the research has been focused only on texture measurement or determination of critical dimensions where feature sizes are less than the wavelength of the light source. In this paper, we propose a new light scattering method to reconstruct the surface topography of grating patterns, using a cascaded machine learning model. The experimental scattering signal can be fed into the machine learning model as the input and the surface topography can be determined as the output. The training dataset, i.e. scattering signals of different surfaces, are generated through a validated rigorous surface scattering model based on a boundary element method (BEM). In this way, the machine learning model can be trained using a big data approach including tens of thousands of datasets, which represent most of the scenarios in real cases. The cascaded machine learning model is designed as a combined top-down, two-layer model implemented using neural networks. The first layer consists of a classification model designed to determine which type of structured surface is being measured, amongst a set of predefined design variants. The second layer contains a regression model, designed to determine the values of the design parameters defining the specific type of structured surface which has been identified, for example the nominal pitch and height of its periodic features. We have developed a prototype system and conducted experiments to verify the proposed method. Structured surfaces containing grating patterns were considered, and different types of gratings were analysed. The results were validated by comparison with measurements performed with atomic force microscopy.

Proceedings Article | 1 April 2020 Presentation + Paper

Smart photogrammetry for three-dimensional shape measurement

Joe Eastwood, Hui Zhang, Mohammad Isa, Danny Sims-Waterhouse, Richard Leach, Samanta Piano

Proceedings Volume 11352, 113520A (2020) https://doi.org/10.1117/12.2556462

KEYWORDS: Cameras, Photogrammetry, Computer aided design, 3D metrology, Additive manufacturing, Clouds, Data acquisition, Metrology, Photography, Computer simulations

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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 | 3 September 2019 Paper

Does interferometry work? A critical look at the foundations of interferometric surface topography measurement

Peter de Groot, Xavier Colonna de Lega, Rong Su, Richard Leach

Proceedings Volume 11102, 111020G (2019) https://doi.org/10.1117/12.2526654

KEYWORDS: Interferometry, Modulation transfer functions, Interferometers, Imaging systems, 3D modeling, Spatial frequencies, Diffraction, Reflectivity, Point spread functions, 3D metrology

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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.

Proceedings Article | 7 March 2019 Paper

All-optical difference engine for in-process defect inspection for roll-to-roll printed electronics

Xiaobing Feng, Rong Su, Tuomas Happonen, Jian Liu, Richard Leach

Proceedings Volume 11053, 1105308 (2019) https://doi.org/10.1117/12.2511140

KEYWORDS: Sensors, Inspection, Printing, Defect inspection, Electronics, Defect detection, Manufacturing, Spatial filters, Photodiodes, Optics manufacturing

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SPIE Journal Paper | 11 October 2017 Open Access

Flexible decoupled camera and projector fringe projection system using inertial sensors

Petros Stavroulakis, Danny Sims-Waterhouse, Samanta Piano, Richard Leach

OE, Vol. 56, Issue 10, 104106, (October 2017) https://doi.org/10.1117/12.10.1117/1.OE.56.10.104106

KEYWORDS: Cameras, Projection systems, Sensors, Clouds, Calibration, Imaging systems, Data acquisition, Computer aided design, Manufacturing, Optical engineering

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Proceedings Article | 23 August 2017 Presentation + Paper

Fusion of light-field and photogrammetric surface form data

Danny Sims-Waterhouse, Samanta Piano, Richard Leach

Proceedings Volume 10373, 1037304 (2017) https://doi.org/10.1117/12.2272999

KEYWORDS: Data fusion, Cameras, Clouds, Photogrammetry, Image fusion, Optical metrology, 3D modeling, Imaging systems, 3D metrology, Photography

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SPIE Journal Paper | 25 July 2017 Open Access

Optimization of surface measurement for metal additive manufacturing using coherence scanning interferometry

Carlos Gomez, Rong Su, Adam Thompson, Jack DiSciacca, Simon Lawes, Richard Leach

OE, Vol. 56, Issue 11, 111714, (July 2017) https://doi.org/10.1117/12.10.1117/1.OE.56.11.111714

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Proceedings Article | 26 June 2017 Paper

Combined use of a priori data for fast system self-calibration of a non-rigid multi-camera fringe projection system

Petros Stavroulakis, Shuxiao Chen, Danny Sims-Waterhouse, Samanta Piano, Nicholas Southon, Patrick Bointon, Richard Leach

Proceedings Volume 10330, 1033006 (2017) https://doi.org/10.1117/12.2269302

KEYWORDS: Motion measurement, Visualization, Calibration, Projection systems, Cameras, 3D metrology, 3D modeling, Modeling

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Proceedings Article | 26 June 2017 Paper

Tolerance on sphere radius for the calibration of the transfer function of coherence scanning interferometry

Rong Su, Jeremy Coupland, Yuhang Wang, Richard Leach

Proceedings Volume 10329, 103290L (2017) https://doi.org/10.1117/12.2272041

KEYWORDS: Analytical research, Spherical lenses, Calibration, Tolerancing, Interferometry, Metrology, Point spread functions, 3D modeling, Interferometers

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Proceedings Article | 26 June 2017 Paper

Experimental comparison of photogrammetry for additive manufactured parts with and without laser speckle projection

D. Sims-Waterhouse, P. Bointon, S. Piano, R. Leach

Proceedings Volume 10329, 103290W (2017) https://doi.org/10.1117/12.2269507

KEYWORDS: Photogrammetry, Speckle, Additive manufacturing, 3D metrology, Clouds, Polymers, Metals, Computer aided design, Cameras, Light sources and illumination, Manufacturing

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Proceedings Article | 8 May 2012 Paper

Application of linear systems theory to characterize coherence scanning interferometry

Rahul Mandal, Kanik Palodhi, Jeremy Coupland, Richard Leach, Daniel Mansfield

Proceedings Volume 8430, 84300T (2012) https://doi.org/10.1117/12.922435

KEYWORDS: Point spread functions, Optical spheres, Electronic filtering, Calibration, Mercury, Spherical lenses, Interferometry, Linear filtering, Image filtering, Refractive index

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Proceedings Article | 5 May 2012 Paper

Determination of the metrological characteristics of optical surface topography measuring instruments

R. Leach, C. Giusca

Proceedings Volume 8430, 84300Q (2012) https://doi.org/10.1117/12.921452

KEYWORDS: Calibration, Metrology, Standards development, Nanolithography, Interferometers, Microscopes, Optical calibration, Confocal microscopy, Optical components, Objectives

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Proceedings Article | 5 May 2012 Paper

Advances in calibration methods for micro- and nanoscale surfaces

R. Leach, C. Giusca, J. Coupland

Proceedings Volume 8430, 84300H (2012) https://doi.org/10.1117/12.928181

KEYWORDS: Calibration, Optical components, Standards development, Optics manufacturing, Nanolithography, Metrology, Scattering, Confocal microscopy, Optical spheres, Manufacturing

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Proceedings Article | 12 January 2009 Paper

Dimensional nanometrology at the National Physical Laboratory

Andrew Yacoot, Richard Leach, Ben Hughes, Claudiu Giusca, Christopher Jones, Alan Wilson

Proceedings Volume 7133, 713345 (2009) https://doi.org/10.1117/12.807994

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Proceedings Article | 5 February 2002 Paper

Traceable measurement of surface texture in the optics industry

Richard Leach

Proceedings Volume 4411, (2002) https://doi.org/10.1117/12.454887

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Proceedings Article | 30 September 1998 Paper

Measurement of a correction for the phase change on reflection due to surface roughness

Richard Leach

Proceedings Volume 3477, (1998) https://doi.org/10.1117/12.323103

KEYWORDS: Reflection, Calibration, Sensors, Optical spheres, Surface roughness, Nanolithography, Integrating spheres, Reflectivity, Diffuse reflectance spectroscopy, Surface finishing

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