2016
Xu, Di; Yao, Jianing; Zhao, Nan; Rolland, Jannick P.
Optical Society of America, 2016, ISBN: 978-1-943580-19-4, (The CEFO project relevant portions were not included in the proceeding but were presented directly at the conference. Presentation slides are available upon request. ).
Abstract | Links | BibTeX | Tags: related, testing
@conference{Xu2016,
title = {Scanning Customized Swept-source Optical Coherence Tomography (SS-OCT) for the Metrology of Freeform Optical Surfaces},
author = {Di Xu and Jianing Yao and Nan Zhao and Jannick P. Rolland},
url = {https://doi.org/10.1364/FIO.2016.FW5H.6},
doi = {10.1364/FIO.2016.FW5H.6},
isbn = {978-1-943580-19-4},
year = {2016},
date = {2016-10-17},
urldate = {2016-10-17},
publisher = {Optical Society of America},
abstract = {A high-precision SS-OCT system with custom scanning configuration was developed for the point cloud metrology of freeform optical surfaces. Capabilities were demonstrated on an Alvarez surface and a measurement precision of λ/20 was achieved.},
note = {The CEFO project relevant portions were not included in the proceeding but were presented directly at the conference. Presentation slides are available upon request. },
keywords = {related, testing},
pubstate = {published},
tppubtype = {conference}
}
A high-precision SS-OCT system with custom scanning configuration was developed for the point cloud metrology of freeform optical surfaces. Capabilities were demonstrated on an Alvarez surface and a measurement precision of λ/20 was achieved.
Moore, D. B.; Fienup, J. R.
Ptychography for optical metrology with limited translation knowledge Journal Article
In: Applied Optics, vol. 55, no. 17, pp. 4596-4610, 2016.
Abstract | Links | BibTeX | Tags: related, testing
@article{Fienup16,
title = {Ptychography for optical metrology with limited translation knowledge},
author = {Moore, D. B. and J. R. Fienup},
url = {https://www.osapublishing.org/ao/abstract.cfm?uri=ao-55-17-4596},
doi = {https://doi.org/10.1364/AO.55.004596},
year = {2016},
date = {2016-06-07},
urldate = {2016-06-07},
journal = {Applied Optics},
volume = {55},
number = {17},
pages = {4596-4610},
abstract = {We introduce unknown-transverse translation diversity phase retrieval: a ptychographic algorithm for optical metrology when a subaperture is translating through a plane conjugate to the exit pupil in a very poorly known fashion. The algorithm estimates the direction of translation and the distance traveled by the subaperture from one point spread function (PSF) to the next. It also estimates unknown point target motion and rotations of the subaperture between PSF acquisitions from the PSF data.},
keywords = {related, testing},
pubstate = {published},
tppubtype = {article}
}
We introduce unknown-transverse translation diversity phase retrieval: a ptychographic algorithm for optical metrology when a subaperture is translating through a plane conjugate to the exit pupil in a very poorly known fashion. The algorithm estimates the direction of translation and the distance traveled by the subaperture from one point spread function (PSF) to the next. It also estimates unknown point target motion and rotations of the subaperture between PSF acquisitions from the PSF data.
Huang, J.; Hindman, H. B.; Rolland, J. P.
In vivo thickness dynamics measurement of tear film lipid and aqueous layers with optical coherence tomography and maximum-likelihood estimation Journal Article
In: Optics Letters, vol. 41, no. 9, pp. 1981-1984 , 2016.
Abstract | Links | BibTeX | Tags: related, testing
@article{Huang16,
title = {In vivo thickness dynamics measurement of tear film lipid and aqueous layers with optical coherence tomography and maximum-likelihood estimation},
author = {Huang, J. and H. B. Hindman and J. P. Rolland},
doi = {https://doi.org/10.1364/OL.41.001981},
year = {2016},
date = {2016-04-15},
urldate = {2016-04-15},
journal = {Optics Letters},
volume = {41},
number = {9},
pages = {1981-1984 },
abstract = {Dry eye disease (DED) is a common ophthalmic condition that is characterized by tear film instability and leads to ocular surface discomfort and visual disturbance. Advancements in the understanding and management of this condition have been limited by our ability to study the tear film secondary to its thin structure and dynamic nature. Here, we report a technique to simultaneously estimate the thickness of both the lipid and aqueous layers of the tear film in vivo using optical coherence tomography and maximum-likelihood estimation. After a blink, the lipid layer was rapidly thickened at an average rate of 10 nm/s
over the first 2.5 s before stabilizing, whereas the aqueous layer continued thinning at an average rate of 0.29 μm/s
of the 10 s blink cycle. Further development of this tear film imaging technique may allow for the elucidation of events that trigger tear film instability in DED.},
keywords = {related, testing},
pubstate = {published},
tppubtype = {article}
}
Dry eye disease (DED) is a common ophthalmic condition that is characterized by tear film instability and leads to ocular surface discomfort and visual disturbance. Advancements in the understanding and management of this condition have been limited by our ability to study the tear film secondary to its thin structure and dynamic nature. Here, we report a technique to simultaneously estimate the thickness of both the lipid and aqueous layers of the tear film in vivo using optical coherence tomography and maximum-likelihood estimation. After a blink, the lipid layer was rapidly thickened at an average rate of 10 nm/s
over the first 2.5 s before stabilizing, whereas the aqueous layer continued thinning at an average rate of 0.29 μm/s
of the 10 s blink cycle. Further development of this tear film imaging technique may allow for the elucidation of events that trigger tear film instability in DED.
over the first 2.5 s before stabilizing, whereas the aqueous layer continued thinning at an average rate of 0.29 μm/s
of the 10 s blink cycle. Further development of this tear film imaging technique may allow for the elucidation of events that trigger tear film instability in DED.
Moore, D. B.; Fienup, J. R.
Subaperture translation estimation accuracy in transverse-translation diversity phase retrieval Journal Article
In: Applied Optics, vol. 55, no. 10, pp. 2526-2536, 2016.
Abstract | Links | BibTeX | Tags: related, testing
@article{ao-55-10-2526.bib,
title = {Subaperture translation estimation accuracy in transverse-translation diversity phase retrieval},
author = {Moore, D.B. and J.R. Fienup},
url = {https://www.osapublishing.org/ao/abstract.cfm?uri=ao-55-10-2526&origin=search},
doi = {10.1364/AO.55.002526},
year = {2016},
date = {2016-03-22},
journal = {Applied Optics},
volume = {55},
number = {10},
pages = {2526-2536},
abstract = {For optical metrology by transverse translation diversity phase retrieval (or ptychography), information theoretic limits on the ability to estimate subaperture translation, essential for accurate metrology, are assessed as a function of the optical aberrations of the system being measured. Special attention is given to the case that an unknown linear phase aberration, or equivalent detector or target motion, is present that varies with each point spread function in the measured data.},
keywords = {related, testing},
pubstate = {published},
tppubtype = {article}
}
For optical metrology by transverse translation diversity phase retrieval (or ptychography), information theoretic limits on the ability to estimate subaperture translation, essential for accurate metrology, are assessed as a function of the optical aberrations of the system being measured. Special attention is given to the case that an unknown linear phase aberration, or equivalent detector or target motion, is present that varies with each point spread function in the measured data.
Mehrotra, K.
Nano-mechanics of Optical Structures for High Laser-Damage Threshold Application PhD Thesis
University of Rochester, 2016.
Abstract | Links | BibTeX | Tags: related, testing
@phdthesis{Mehrotra2016,
title = {Nano-mechanics of Optical Structures for High Laser-Damage Threshold Application},
author = {Mehrotra, K.},
url = {https://www.lle.rochester.edu/media/publications/documents/theses/Mehrotra.pdf},
year = {2016},
date = {2016-01-13},
urldate = {2016-01-13},
address = {Department of Mechanical Engineering},
school = {University of Rochester},
abstract = {Nano-structured optical materials such as amorphous silica diffraction gratings on multilayer
dielectric (MLD) thin films are critical components and performance enhancers in high-power
laser applications such as in inertial confinement fusion experiments. We use nano-indentation,
electron microscopy and finite-element (2D and 3D) simulations to measure and observe the
nano-mechanical material properties (elastic, plastic, and fracture) of nm-level features along
with their associated defects in important optical components that include single layer and multilayer
oxide films, and optical diffraction gratings. Our work reveals that elasticity, ductility and
fracture at the nm-level can be studied separately, in contrast to micromechanical deformation;
that SEM plays an important role in identifying relevant features; that in addition to
characterization, nanoindentation may be useful as a diagnostic tool; and that numerical
simulations naturally complement the experimental nano-mechanics to model the complex nmlevel
response of optical nanostructures.},
type = {related},
keywords = {related, testing},
pubstate = {published},
tppubtype = {phdthesis}
}
Nano-structured optical materials such as amorphous silica diffraction gratings on multilayer
dielectric (MLD) thin films are critical components and performance enhancers in high-power
laser applications such as in inertial confinement fusion experiments. We use nano-indentation,
electron microscopy and finite-element (2D and 3D) simulations to measure and observe the
nano-mechanical material properties (elastic, plastic, and fracture) of nm-level features along
with their associated defects in important optical components that include single layer and multilayer
oxide films, and optical diffraction gratings. Our work reveals that elasticity, ductility and
fracture at the nm-level can be studied separately, in contrast to micromechanical deformation;
that SEM plays an important role in identifying relevant features; that in addition to
characterization, nanoindentation may be useful as a diagnostic tool; and that numerical
simulations naturally complement the experimental nano-mechanics to model the complex nmlevel
response of optical nanostructures.
dielectric (MLD) thin films are critical components and performance enhancers in high-power
laser applications such as in inertial confinement fusion experiments. We use nano-indentation,
electron microscopy and finite-element (2D and 3D) simulations to measure and observe the
nano-mechanical material properties (elastic, plastic, and fracture) of nm-level features along
with their associated defects in important optical components that include single layer and multilayer
oxide films, and optical diffraction gratings. Our work reveals that elasticity, ductility and
fracture at the nm-level can be studied separately, in contrast to micromechanical deformation;
that SEM plays an important role in identifying relevant features; that in addition to
characterization, nanoindentation may be useful as a diagnostic tool; and that numerical
simulations naturally complement the experimental nano-mechanics to model the complex nmlevel
response of optical nanostructures.
Yao, J.; Thompson, K.; Ma, B.; Rolland, J. P.
Volumetric rendering and metrology of spherical gradient refractive index lens imaged by angular scan optical coherence tomography system Journal Article
In: Optics Express, vol. 24, no. 17, pp. 19388-19404, 2016.
Abstract | Links | BibTeX | Tags: related, testing
@article{YAO2016,
title = {Volumetric rendering and metrology of spherical gradient refractive index lens imaged by angular scan optical coherence tomography system},
author = {Yao, J. and K. Thompson and B. Ma and J. P. Rolland},
url = {https://centerfreeformoptics.org/wp-content/uploads/2017/01/oe-24-17-19388-1.pdf, Full paper},
doi = {10.1364/OE.24.019388 },
year = {2016},
date = {2016-00-00},
journal = {Optics Express},
volume = {24},
number = {17},
pages = {19388-19404},
abstract = {In this paper, we develop the methodology, including the refraction correction,
geometrical thickness correction, coordinate transformation, and layer segmentation
algorithms, for 3D rendering and metrology of a layered spherical gradient refractive index
(S-GRIN) lens based on the imaging data collected by an angular scan optical coherence
tomography (OCT) system. The 3D mapping and rendering enables direct 3D visualization
and internal defect inspection of the lens. The metrology provides assessment of the surface
geometry, the lens thickness, the radii of curvature of the internal layer interfaces, and the
misalignment of the internal S-GRIN distribution with respect to the lens surface. The OCT
metrology results identify the manufacturing defects, and enable targeted process
development for optimizing the manufacturing parameters. The newly fabricated S-GRIN
lenses show up to a 7x spherical aberration reduction that allows a significantly increased
utilizable effective aperture.
© 2016 Optical Society of America
OCIS codes: (120.0120) Instrumentation, measurement, and metrology; (110.4500) Optical coherence tomography;
(120.4630) Optical inspection; (110.0110) Imaging systems. },
keywords = {related, testing},
pubstate = {published},
tppubtype = {article}
}
In this paper, we develop the methodology, including the refraction correction,
geometrical thickness correction, coordinate transformation, and layer segmentation
algorithms, for 3D rendering and metrology of a layered spherical gradient refractive index
(S-GRIN) lens based on the imaging data collected by an angular scan optical coherence
tomography (OCT) system. The 3D mapping and rendering enables direct 3D visualization
and internal defect inspection of the lens. The metrology provides assessment of the surface
geometry, the lens thickness, the radii of curvature of the internal layer interfaces, and the
misalignment of the internal S-GRIN distribution with respect to the lens surface. The OCT
metrology results identify the manufacturing defects, and enable targeted process
development for optimizing the manufacturing parameters. The newly fabricated S-GRIN
lenses show up to a 7x spherical aberration reduction that allows a significantly increased
utilizable effective aperture.
© 2016 Optical Society of America
OCIS codes: (120.0120) Instrumentation, measurement, and metrology; (110.4500) Optical coherence tomography;
(120.4630) Optical inspection; (110.0110) Imaging systems.
geometrical thickness correction, coordinate transformation, and layer segmentation
algorithms, for 3D rendering and metrology of a layered spherical gradient refractive index
(S-GRIN) lens based on the imaging data collected by an angular scan optical coherence
tomography (OCT) system. The 3D mapping and rendering enables direct 3D visualization
and internal defect inspection of the lens. The metrology provides assessment of the surface
geometry, the lens thickness, the radii of curvature of the internal layer interfaces, and the
misalignment of the internal S-GRIN distribution with respect to the lens surface. The OCT
metrology results identify the manufacturing defects, and enable targeted process
development for optimizing the manufacturing parameters. The newly fabricated S-GRIN
lenses show up to a 7x spherical aberration reduction that allows a significantly increased
utilizable effective aperture.
© 2016 Optical Society of America
OCIS codes: (120.0120) Instrumentation, measurement, and metrology; (110.4500) Optical coherence tomography;
(120.4630) Optical inspection; (110.0110) Imaging systems.
2015
Huang, J.; Yao, J.; Cirucci, N.; Ivanov, T.; Rolland, J. P.
Performance analysis of optical coherence tomography in the context of a thickness estimation task Journal Article
In: Journal of Biomedical Optics, vol. 20, no. 12, pp. 121306, 2015.
Abstract | Links | BibTeX | Tags: related, testing
@article{Huang15,
title = {Performance analysis of optical coherence tomography in the context of a thickness estimation task},
author = {Huang, J. and J. Yao and N. Cirucci and T. Ivanov and J. P. Rolland},
url = {https://www.spiedigitallibrary.org/journals/journal-of-biomedical-optics/volume-20/issue-12/121306/Performance-analysis-of-optical-coherence-tomography-in-the-context-of/10.1117/1.JBO.20.12.121306.full},
doi = {https://doi.org/10.1117/1.JBO.20.12.121306},
year = {2015},
date = {2015-12-01},
urldate = {2015-12-01},
journal = {Journal of Biomedical Optics},
volume = {20},
number = {12},
pages = {121306},
abstract = {Thickness estimation is a common task in optical coherence tomography (OCT). This study discusses and quantifies the intensity noise of three commonly used broadband sources, such as a supercontinuum source, a superluminescent diode (SLD), and a swept source. The performance of the three optical sources was evaluated for a thickness estimation task using both the fast Fourier transform (FFT) and maximum-likelihood (ML) estimators. We find that the source intensity noise has less impact on a thickness estimation task compared to the width of the axial point-spread function (PSF) and the trigger jittering noise of a swept source. Findings further show that the FFT estimator yields biased estimates, which can be as large as 10% of the thickness under test in the worst case. The ML estimator is by construction asymptotically unbiased and displays a 10× improvement in precision for both the supercontinuum and SLD sources. The ML estimator also shows the ability to estimate thickness that is at least 10× thinner compared to the FFT estimator. Finally, findings show that a supercontinuum source combined with the ML estimator enables unbiased nanometer-class thickness estimation with nanometer-scale precision.},
keywords = {related, testing},
pubstate = {published},
tppubtype = {article}
}
Thickness estimation is a common task in optical coherence tomography (OCT). This study discusses and quantifies the intensity noise of three commonly used broadband sources, such as a supercontinuum source, a superluminescent diode (SLD), and a swept source. The performance of the three optical sources was evaluated for a thickness estimation task using both the fast Fourier transform (FFT) and maximum-likelihood (ML) estimators. We find that the source intensity noise has less impact on a thickness estimation task compared to the width of the axial point-spread function (PSF) and the trigger jittering noise of a swept source. Findings further show that the FFT estimator yields biased estimates, which can be as large as 10% of the thickness under test in the worst case. The ML estimator is by construction asymptotically unbiased and displays a 10× improvement in precision for both the supercontinuum and SLD sources. The ML estimator also shows the ability to estimate thickness that is at least 10× thinner compared to the FFT estimator. Finally, findings show that a supercontinuum source combined with the ML estimator enables unbiased nanometer-class thickness estimation with nanometer-scale precision.
Yao, J.; Huang, J.; Meemon, P.; Ponting, M.; Rolland, J. P.
In: Opt. Express, vol. 23, no. 23, pp. 30149-30164, 2015.
Abstract | Links | BibTeX | Tags: related, testing
@article{YAO15b,
title = {Simultaneous estimation of thickness and refractive index of layered gradient refractive index optics using a hybrid confocal-scan swept-source optical coherence tomography system},
author = {Yao, J. and J. Huang and P. Meemon and M. Ponting and J. P. Rolland},
doi = {https://doi.org/10.1364/OE.23.030149},
year = {2015},
date = {2015-11-10},
urldate = {2015-11-10},
journal = {Opt. Express},
volume = {23},
number = {23},
pages = {30149-30164},
abstract = {A hybrid confocal-scan swept-source optical coherence tomography metrology system was conceived for simultaneous measurements of the refractive index and thickness profiles of polymeric layered gradient refractive index (GRIN) optics. An uncertainty analysis predicts the metrology capability of the system and guides the selection of an optimum working numerical aperture. Experimental results on both a monolithic and a GRIN layered sheet are demonstrated to be in close agreement with theoretical predictions. Index measurement precision reached 0.0001 and 0.0008 for measuring 2.8 mm and ~300 µm thick layers, respectively. The thicknesses of these layers were simultaneously measured with a precision of 0.28 and 0.17 µm, respectively.},
keywords = {related, testing},
pubstate = {published},
tppubtype = {article}
}
A hybrid confocal-scan swept-source optical coherence tomography metrology system was conceived for simultaneous measurements of the refractive index and thickness profiles of polymeric layered gradient refractive index (GRIN) optics. An uncertainty analysis predicts the metrology capability of the system and guides the selection of an optimum working numerical aperture. Experimental results on both a monolithic and a GRIN layered sheet are demonstrated to be in close agreement with theoretical predictions. Index measurement precision reached 0.0001 and 0.0008 for measuring 2.8 mm and ~300 µm thick layers, respectively. The thicknesses of these layers were simultaneously measured with a precision of 0.28 and 0.17 µm, respectively.
Moore, D. B.; Fienup, J. R.
Sub-Aperture Position Estimation in Transverse-Translation Diversity Wavefront Sensing Conference
2015.
Abstract | Links | BibTeX | Tags: related, testing
@conference{Moore_AOMS_2015,
title = {Sub-Aperture Position Estimation in Transverse-Translation Diversity Wavefront Sensing},
author = {D. B. Moore and J.R. Fienup},
doi = {10.1364/AOMS.2015.AOM3F.4},
year = {2015},
date = {2015-10-21},
journal = {Imaging and Applied Optics 2015 OSA Technical Digest (online) (Optical Society of America, 2015)},
pages = {AOM3F.4},
abstract = {Image-based wavefront sensing involving a sub-aperture translating in an unknown fashion in a pupil plane is demonstrated experimentally in the case that the target is also translating in an unknown fashion.},
keywords = {related, testing},
pubstate = {published},
tppubtype = {conference}
}
Image-based wavefront sensing involving a sub-aperture translating in an unknown fashion in a pupil plane is demonstrated experimentally in the case that the target is also translating in an unknown fashion.
Yao, Jianing; Xu, Di; Zhao, Nan; Rolland, Jannick P.
Proceedings of SPIE, vol. 9633, no. 96331A, 2015.
Abstract | Links | BibTeX | Tags: related, testing
@conference{Yao15optifab,
title = {Freeform metrology using swept-source optical coherence tomography with custom pupil-relay precision scanning configuration},
author = {Jianing Yao and Di Xu and Nan Zhao and Jannick P. Rolland},
doi = {https://doi.org/10.1117/12.2195939},
year = {2015},
date = {2015-10-11},
urldate = {2015-10-11},
booktitle = {Proceedings of SPIE},
volume = {9633},
number = {96331A},
abstract = {The recent advances in the optics manufacturing industry to achieve the capability of fabricating rotationally nonsymmetric optical quality surfaces have considerably stimulated the optical designs with freeform components. This opens up new horizons for novel optical systems with larger fields of view and higher performance, or significantly more compact in volume at equal performance compared to conventional systems. A bottleneck to the broad industrial applications of freeform optics remains the lack of a high performance optical metrology tool capable of measuring significant surface departures and slopes of the parts. To address this issue, we have developed a fiber-based swept-source optical coherence tomography (SS-OCT) system for point-cloud freeform metrology, where two-axis galvanometer scanners are leveraged for high-speed lateral scans. We specifically designed a custom all-reflective achromatic pupil relay system to achieve a diffraction-limited scanning configuration. Coupled with a large field-of-view (FOV) telecentric scan lens, the imaging covers 28.9 mm × 28.9 mm FOV with 35 μm lateral resolution and more than 600 μm depth of focus. Freeform metrology is demonstrated for an Alvarez surface of 400 μm surface sag. The high sensitivity of the SS-OCT system allows for capturing the slope variations of the part up to the maximum slope that is 5 degrees in this case. Specific surface reconstruction, rendering and fitting algorithms were developed to evaluate the metrology results and investigate the accuracy and precision of the measurements.},
keywords = {related, testing},
pubstate = {published},
tppubtype = {conference}
}
The recent advances in the optics manufacturing industry to achieve the capability of fabricating rotationally nonsymmetric optical quality surfaces have considerably stimulated the optical designs with freeform components. This opens up new horizons for novel optical systems with larger fields of view and higher performance, or significantly more compact in volume at equal performance compared to conventional systems. A bottleneck to the broad industrial applications of freeform optics remains the lack of a high performance optical metrology tool capable of measuring significant surface departures and slopes of the parts. To address this issue, we have developed a fiber-based swept-source optical coherence tomography (SS-OCT) system for point-cloud freeform metrology, where two-axis galvanometer scanners are leveraged for high-speed lateral scans. We specifically designed a custom all-reflective achromatic pupil relay system to achieve a diffraction-limited scanning configuration. Coupled with a large field-of-view (FOV) telecentric scan lens, the imaging covers 28.9 mm × 28.9 mm FOV with 35 μm lateral resolution and more than 600 μm depth of focus. Freeform metrology is demonstrated for an Alvarez surface of 400 μm surface sag. The high sensitivity of the SS-OCT system allows for capturing the slope variations of the part up to the maximum slope that is 5 degrees in this case. Specific surface reconstruction, rendering and fitting algorithms were developed to evaluate the metrology results and investigate the accuracy and precision of the measurements.
Huang, J.; Yao, J.; Cirucci, N. M.; Ivanov, T.; Rolland, J. P.
Thickness estimation with optical coherence tomography and statistical decision theory Conference
proceeding of SPIE, vol. 9633, no. 96330P, 2015.
Abstract | Links | BibTeX | Tags: related, testing
@conference{Huangoptifab15,
title = {Thickness estimation with optical coherence tomography and statistical decision theory},
author = {Huang, J. and J. Yao and N.M. Cirucci and T. Ivanov and J.P. Rolland},
doi = {https://doi.org/10.1117/12.2195969},
year = {2015},
date = {2015-10-11},
urldate = {2015-10-11},
booktitle = {proceeding of SPIE},
volume = {9633},
number = {96330P},
abstract = {Thickness estimation, which has a broad range of applications, plays an important role in the field of optical metrology. In this study, we investigate a new approach—combining optical coherence tomography (OCT) and statistical decision theory—for thickness estimation. We first discussed and quantified the intensity noise of three commonly used broadband sources, a super-continuum source, a super-luminescent diode (SLD), and a swept source. Furthermore, a maximum-likelihood (ML) estimator was implemented to interpret the OCT raw data. Based on the mathematical model and the ML estimator, simulations were set up to investigate the impact of different broadband sources in OCT for a thickness estimation task. We then validated the theoretical framework with physical phantoms. Results demonstrate unbiased nanometer-class thickness estimates with the ML estimator. The framework can be potentially used for film and surface shape metrology.},
keywords = {related, testing},
pubstate = {published},
tppubtype = {conference}
}
Thickness estimation, which has a broad range of applications, plays an important role in the field of optical metrology. In this study, we investigate a new approach—combining optical coherence tomography (OCT) and statistical decision theory—for thickness estimation. We first discussed and quantified the intensity noise of three commonly used broadband sources, a super-continuum source, a super-luminescent diode (SLD), and a swept source. Furthermore, a maximum-likelihood (ML) estimator was implemented to interpret the OCT raw data. Based on the mathematical model and the ML estimator, simulations were set up to investigate the impact of different broadband sources in OCT for a thickness estimation task. We then validated the theoretical framework with physical phantoms. Results demonstrate unbiased nanometer-class thickness estimates with the ML estimator. The framework can be potentially used for film and surface shape metrology.
Canavesi, C.; Cogliati, A.; Hayes, A.; Santhanam, A. P.; Tankam, P.; Rolland, J. P.
Proceedings of the SPIE, vol. 9633, no. 96330O, 2015.
Abstract | Links | BibTeX | Tags: related, testing
@conference{Canavesioptifab15,
title = {Gabor-domain optical coherence microscopy with integrated dual-axis MEMS scanner for fast 3D imaging and metrology},
author = {Canavesi, C. and A. Cogliati and A. Hayes and A.P. Santhanam and P. Tankam and J.P. Rolland},
doi = {https://doi.org/10.1117/12.2195828},
year = {2015},
date = {2015-10-11},
urldate = {2015-10-11},
booktitle = {Proceedings of the SPIE},
volume = {9633},
number = {96330O},
abstract = {Fast, robust, nondestructive 3D imaging is needed for characterization of microscopic structures in industrial and clinical applications. A custom micro-electromechanical system (MEMS)-based 2D scanner system was developed to achieve 55 kHz A-scan acquisition in a Gabor-domain optical coherence microscopy (GD-OCM) instrument with a novel multilevel GPU architecture for high-speed imaging. GD-OCM yields high-definition volumetric imaging with dynamic depth of focusing through a bio-inspired liquid lens-based microscope design, which has no moving parts and is suitable for use in a manufacturing setting or in a medical environment. A dual-axis MEMS mirror was chosen to replace two single-axis galvanometer mirrors; as a result, the astigmatism caused by the mismatch between the optical pupil and the scanning location was eliminated and a 12x reduction in volume of the scanning system was achieved. Imaging at an invariant resolution of 2 μm was demonstrated throughout a volume of 1 × 1 × 0.6 mm3, acquired in less than 2 minutes. The MEMS-based scanner resulted in improved image quality, increased robustness and lighter weight of the system – all factors that are critical for on-field deployment. A custom integrated feedback system consisting of a laser diode and a position-sensing detector was developed to investigate the impact of the resonant frequency of the MEMS and the driving signal of the scanner on the movement of the mirror. Results on the metrology of manufactured materials and characterization of tissue samples with GD-OCM are presented.},
keywords = {related, testing},
pubstate = {published},
tppubtype = {conference}
}
Fast, robust, nondestructive 3D imaging is needed for characterization of microscopic structures in industrial and clinical applications. A custom micro-electromechanical system (MEMS)-based 2D scanner system was developed to achieve 55 kHz A-scan acquisition in a Gabor-domain optical coherence microscopy (GD-OCM) instrument with a novel multilevel GPU architecture for high-speed imaging. GD-OCM yields high-definition volumetric imaging with dynamic depth of focusing through a bio-inspired liquid lens-based microscope design, which has no moving parts and is suitable for use in a manufacturing setting or in a medical environment. A dual-axis MEMS mirror was chosen to replace two single-axis galvanometer mirrors; as a result, the astigmatism caused by the mismatch between the optical pupil and the scanning location was eliminated and a 12x reduction in volume of the scanning system was achieved. Imaging at an invariant resolution of 2 μm was demonstrated throughout a volume of 1 × 1 × 0.6 mm3, acquired in less than 2 minutes. The MEMS-based scanner resulted in improved image quality, increased robustness and lighter weight of the system – all factors that are critical for on-field deployment. A custom integrated feedback system consisting of a laser diode and a position-sensing detector was developed to investigate the impact of the resonant frequency of the MEMS and the driving signal of the scanner on the movement of the mirror. Results on the metrology of manufactured materials and characterization of tissue samples with GD-OCM are presented.
Duma, V.; Tankam, P.; Huang, J.; Won, J.; J. P. Rolland,
Optimization of galvanometer scanning for optical coherence tomography Journal Article
In: Applied Optics, vol. 54, no. 17, pp. 5495-5507, 2015.
Abstract | Links | BibTeX | Tags: related, testing
@article{DUMA15,
title = {Optimization of galvanometer scanning for optical coherence tomography},
author = {Duma, V. and P. Tankam and J. Huang and J. Won and J. P. Rolland,},
doi = {https://doi.org/10.1364/AO.54.005495},
year = {2015},
date = {2015-06-10},
urldate = {2015-06-10},
journal = {Applied Optics},
volume = {54},
number = {17},
pages = {5495-5507},
abstract = {We study experimentally the effective duty cycle of galvanometer-based scanners (GSs) with regard to three main parameters of the scanning process: theoretical/imposed duty cycle (of the input signal), scan frequency, and scan amplitude. Sawtooth and triangular input signals for the device are considered. The effects of the mechanical inertia of the oscillatory element of the GS are analyzed and their consequences are discussed in the context of optical coherence tomography (OCT) imaging. When the theoretical duty cycle and the scan amplitude are increased to the limit, the saturation of the device is demonstrated for a useful range of scan frequencies by direct measurement of the position of the galvomirror. Investigations of OCT imaging of large samples also validate this saturation, as examplified by the gaps/blurred portions obtained between neighboring images when using both triangular and sawtooth scanning at high scan frequencies. For this latter aspect, the necessary overlap between neighboring B-scans, and therefore between the corresponding volumetric reconstructions of the sample, are evaluated and implemented with regard to the same parameters of the scanning process. OCT images that are free of these artifacts are thus obtained.},
keywords = {related, testing},
pubstate = {published},
tppubtype = {article}
}
We study experimentally the effective duty cycle of galvanometer-based scanners (GSs) with regard to three main parameters of the scanning process: theoretical/imposed duty cycle (of the input signal), scan frequency, and scan amplitude. Sawtooth and triangular input signals for the device are considered. The effects of the mechanical inertia of the oscillatory element of the GS are analyzed and their consequences are discussed in the context of optical coherence tomography (OCT) imaging. When the theoretical duty cycle and the scan amplitude are increased to the limit, the saturation of the device is demonstrated for a useful range of scan frequencies by direct measurement of the position of the galvomirror. Investigations of OCT imaging of large samples also validate this saturation, as examplified by the gaps/blurred portions obtained between neighboring images when using both triangular and sawtooth scanning at high scan frequencies. For this latter aspect, the necessary overlap between neighboring B-scans, and therefore between the corresponding volumetric reconstructions of the sample, are evaluated and implemented with regard to the same parameters of the scanning process. OCT images that are free of these artifacts are thus obtained.
Yao, J.; Meemon, P.; Ponting, M.; Rolland, J. P.
Metrology of 3D freeform spherical gradient index preforms Conference
Imaging and Applied Optics 2015OSA Technical Digest, no. FT3B.3 , 2015, (Imaging and Applied Optics 2015, OSA Technical Digest, paper FT3B.3 (2015). ).
Abstract | Links | BibTeX | Tags: related, testing
@conference{Yao15pa,
title = {Metrology of 3D freeform spherical gradient index preforms},
author = {Yao, J. and P. Meemon and M. Ponting and J. P. Rolland},
doi = {https://doi.org/10.1364/FREEFORM.2015.FT3B.3},
year = {2015},
date = {2015-06-08},
urldate = {2015-06-08},
booktitle = {Imaging and Applied Optics 2015OSA Technical Digest},
number = {FT3B.3 },
abstract = {We present an angular-scan swept-source optical coherence tomography system for 3D imaging and concentricity characterization of two generations of spherical gradient index preforms with a method to decouple the physical thickness and the index measurements.},
note = {Imaging and Applied Optics 2015, OSA Technical Digest, paper FT3B.3 (2015). },
keywords = {related, testing},
pubstate = {published},
tppubtype = {conference}
}
We present an angular-scan swept-source optical coherence tomography system for 3D imaging and concentricity characterization of two generations of spherical gradient index preforms with a method to decouple the physical thickness and the index measurements.
Evans, C. J.; Browy, E. C.; Childs, T. H. C.; Paul, E.
Interferometric measurements of single crystal diamond tool wear Journal Article
In: CIRP Annals - Manufacturing Technology, vol. 64, pp. 125-128, 2015.
Abstract | Links | BibTeX | Tags: related, testing
@article{Evans15,
title = {Interferometric measurements of single crystal diamond tool wear},
author = {Evans, C. J. and E.C. Browy and T.H.C. Childs and E. Paul },
doi = {https://doi.org/10.1016/j.cirp.2015.04.066},
year = {2015},
date = {2015-05-04},
urldate = {2015-05-04},
journal = {CIRP Annals - Manufacturing Technology},
volume = {64},
pages = {125-128},
abstract = {Interferometric measurements of plunge cuts made in a reference component intermittently during cutting tool wear tests allow measurement of the detail of tool edge recession without removing the tool from the machine. Hence the evolution of the tool wear can be evaluated with a resolution of less than 5 nm. A plunge cut using the new tool is subtracted from subsequent measurements, providing a direct measure of wear and removing bias from the scanning white light interferometer that would arise from non-zero slopes in the field of view. The method is illustrated with results from single crystal diamond tool wear tests when machining a family of nickel-copper alloys of varying composition. The dominant wear mechanism depends on the alloy and the cutting parameters. Nose flattening, leading edge recession, chipping, and formation of Pekelharing grooves can all be identified.},
keywords = {related, testing},
pubstate = {published},
tppubtype = {article}
}
Interferometric measurements of plunge cuts made in a reference component intermittently during cutting tool wear tests allow measurement of the detail of tool edge recession without removing the tool from the machine. Hence the evolution of the tool wear can be evaluated with a resolution of less than 5 nm. A plunge cut using the new tool is subtracted from subsequent measurements, providing a direct measure of wear and removing bias from the scanning white light interferometer that would arise from non-zero slopes in the field of view. The method is illustrated with results from single crystal diamond tool wear tests when machining a family of nickel-copper alloys of varying composition. The dominant wear mechanism depends on the alloy and the cutting parameters. Nose flattening, leading edge recession, chipping, and formation of Pekelharing grooves can all be identified.
Huang, J.; Tankam, P.; Hindman, H. B.; Aquavella, J. V.; Clarkson, E.; Kupinski, M. A.; Rolland, J. P.
Tear film thickness estimation using optical coherence tomography and maximum-likelihood estimation Presentation
02.05.2015.
Abstract | Links | BibTeX | Tags: related, testing
@misc{Huangarvo,
title = {Tear film thickness estimation using optical coherence tomography and maximum-likelihood estimation},
author = {Huang, J. and P. Tankam and H. B. Hindman and J. V. Aquavella and E. Clarkson and M. A. Kupinski and J. P. Rolland},
doi = {10.1117/12.2083160},
year = {2015},
date = {2015-05-02},
urldate = {2015-05-02},
abstract = {In biophotonics imaging, one important and quantitative task is layer-thickness estimation. In this study, we investigate the approach of combining optical coherence tomography and a maximum-likelihood (ML) estimator for layer thickness estimation in the context of tear film imaging. The motivation of this study is to extend our understanding of tear film dynamics, which is the prerequisite to advance the management of Dry Eye Disease, through the simultaneous estimation of the thickness of the tear film lipid and aqueous layers. The estimator takes into account the different statistical processes associated with the imaging chain. We theoretically investigated the impact of key system parameters, such as the axial point spread functions (PSF) and various sources of noise on measurement uncertainty. Simulations show that an OCT system with a 1 μm axial PSF (FWHM) allows unbiased estimates down to nanometers with nanometer precision. In implementation, we built a customized Fourier domain OCT system that operates in the 600 to 1000 nm spectral window and achieves 0.93 micron axial PSF in corneal epithelium. We then validated the theoretical framework with physical phantoms made of custom optical coatings, with layer thicknesses from tens of nanometers to microns. Results demonstrate unbiased nanometer-class thickness estimates in three different physical phantoms.},
keywords = {related, testing},
pubstate = {published},
tppubtype = {presentation}
}
In biophotonics imaging, one important and quantitative task is layer-thickness estimation. In this study, we investigate the approach of combining optical coherence tomography and a maximum-likelihood (ML) estimator for layer thickness estimation in the context of tear film imaging. The motivation of this study is to extend our understanding of tear film dynamics, which is the prerequisite to advance the management of Dry Eye Disease, through the simultaneous estimation of the thickness of the tear film lipid and aqueous layers. The estimator takes into account the different statistical processes associated with the imaging chain. We theoretically investigated the impact of key system parameters, such as the axial point spread functions (PSF) and various sources of noise on measurement uncertainty. Simulations show that an OCT system with a 1 μm axial PSF (FWHM) allows unbiased estimates down to nanometers with nanometer precision. In implementation, we built a customized Fourier domain OCT system that operates in the 600 to 1000 nm spectral window and achieves 0.93 micron axial PSF in corneal epithelium. We then validated the theoretical framework with physical phantoms made of custom optical coatings, with layer thicknesses from tens of nanometers to microns. Results demonstrate unbiased nanometer-class thickness estimates in three different physical phantoms.
Leach, R.; Evans, C.; He, L.; Davies, A.; Duparre, A.; Henning, A.; Jones, C.; O'Connor, D.
Open Questions in Surface Topography Measurement: a roadmap Journal Article
In: Surface Topography: Metrology and Properties, vol. 3, no. 1, pp. 013001, 2015.
Abstract | Links | BibTeX | Tags: related, testing
@article{Leach15,
title = {Open Questions in Surface Topography Measurement: a roadmap},
author = {Leach, R. and C. Evans and L. He and A. Davies and A. Duparre and A. Henning and C. Jones and D. O'Connor},
doi = {10.1088/2051-672X/3/1/013001},
year = {2015},
date = {2015-03-31},
urldate = {2015-03-31},
journal = {Surface Topography: Metrology and Properties},
volume = {3},
number = {1},
pages = {013001},
abstract = {Control of surface topography has always been of vital importance for manufacturing and many other engineering and scientific disciplines. However, despite over one hundred years of quantitative surface topography measurement, there are still many open questions. At the top of the list of questions is 'Are we getting the right answer?' This begs the obvious question 'How would we know?' There are many other questions relating to applications, the appropriateness of a technique for a given scenario, or the relationship between a particular analysis and the function of the surface. In this first 'open questions' article we have gathered together some experts in surface topography measurement and asked them to address timely, unresolved questions about the subject. We hope that their responses will go some way to answer these questions, address areas where further research is required, and look at the future of the subject. The first section 'Spatial content characterization for precision surfaces' addresses the need to characterise the spatial content of precision surfaces. Whilst we have been manufacturing optics for centuries, there still isn't a consensus on how to specify the surface for manufacture. The most common three methods for spatial characterisation are reviewed and compared, and the need for further work on quantifying measurement uncertainties is highlighted. The article is focussed on optical surfaces, but the ideas are more pervasive. Different communities refer to 'figure, mid-spatial frequencies, and finish' and 'form, waviness, and roughness', but the mathematics are identical. The second section 'Light scattering methods' is focussed on light scattering techniques; an important topic with in-line metrology becoming essential in many manufacturing scenarios. The potential of scattering methods has long been recognized; in the 'smooth surface limit' functionally significant relationships can be derived from first principles for statistically stationary, random surfaces. For rougher surfaces, correlations can be found experimentally for specific manufacturing processes. Improvements in computational methods encourage us to revisit light scattering as a powerful and versatile tool to investigate surface and thin film topographies, potentially providing information on both topography and defects over large areas at high speed. Future scattering techniques will be applied for complex film systems and for sub-surface damage measurement, but more research is required to quantify and standardise such measurements. A fundamental limitation of all topography measurement systems is their finite spatial bandwidth, which limits the slopes that they can detect. The third section 'Optical measurements of surfaces containing high slope angles' discusses this limitation and potential methods to overcome it. In some cases, a rough surface can allow measurement of slopes outside the classical optics limit, but more research is needed to fully understand this process. The last section 'What are the challenges for high dynamic range surface measurement?' presents the challenge facing metrologists by the use of surfaces that need measurement systems with very high spatial and temporal bandwidths, for example, those found in roll-to-roll manufacturing. High resolution, large areas and fast measurement times are needed, and these needs are unlikely to be fulfilled by developing a single all-purpose instrument. A toolbox of techniques needs to be developed which can be applied for any specific manufacturing scenario. The functional significance of surface topography has been known for centuries. Mirrors are smooth. Sliding behaviour depends on roughness. We have been measuring surfaces for centuries, but we still face many challenges. New manufacturing paradigms suggest that we need to make rapid measurements online that relate to the functional performance of the surface. This first 'open questions' collection addresses a subset of the challenges facing the surface metrology community. There are many more challenges which we would like to address in future 'open questions' articles. We welcome your feedback and your suggestions.},
keywords = {related, testing},
pubstate = {published},
tppubtype = {article}
}
Control of surface topography has always been of vital importance for manufacturing and many other engineering and scientific disciplines. However, despite over one hundred years of quantitative surface topography measurement, there are still many open questions. At the top of the list of questions is 'Are we getting the right answer?' This begs the obvious question 'How would we know?' There are many other questions relating to applications, the appropriateness of a technique for a given scenario, or the relationship between a particular analysis and the function of the surface. In this first 'open questions' article we have gathered together some experts in surface topography measurement and asked them to address timely, unresolved questions about the subject. We hope that their responses will go some way to answer these questions, address areas where further research is required, and look at the future of the subject. The first section 'Spatial content characterization for precision surfaces' addresses the need to characterise the spatial content of precision surfaces. Whilst we have been manufacturing optics for centuries, there still isn't a consensus on how to specify the surface for manufacture. The most common three methods for spatial characterisation are reviewed and compared, and the need for further work on quantifying measurement uncertainties is highlighted. The article is focussed on optical surfaces, but the ideas are more pervasive. Different communities refer to 'figure, mid-spatial frequencies, and finish' and 'form, waviness, and roughness', but the mathematics are identical. The second section 'Light scattering methods' is focussed on light scattering techniques; an important topic with in-line metrology becoming essential in many manufacturing scenarios. The potential of scattering methods has long been recognized; in the 'smooth surface limit' functionally significant relationships can be derived from first principles for statistically stationary, random surfaces. For rougher surfaces, correlations can be found experimentally for specific manufacturing processes. Improvements in computational methods encourage us to revisit light scattering as a powerful and versatile tool to investigate surface and thin film topographies, potentially providing information on both topography and defects over large areas at high speed. Future scattering techniques will be applied for complex film systems and for sub-surface damage measurement, but more research is required to quantify and standardise such measurements. A fundamental limitation of all topography measurement systems is their finite spatial bandwidth, which limits the slopes that they can detect. The third section 'Optical measurements of surfaces containing high slope angles' discusses this limitation and potential methods to overcome it. In some cases, a rough surface can allow measurement of slopes outside the classical optics limit, but more research is needed to fully understand this process. The last section 'What are the challenges for high dynamic range surface measurement?' presents the challenge facing metrologists by the use of surfaces that need measurement systems with very high spatial and temporal bandwidths, for example, those found in roll-to-roll manufacturing. High resolution, large areas and fast measurement times are needed, and these needs are unlikely to be fulfilled by developing a single all-purpose instrument. A toolbox of techniques needs to be developed which can be applied for any specific manufacturing scenario. The functional significance of surface topography has been known for centuries. Mirrors are smooth. Sliding behaviour depends on roughness. We have been measuring surfaces for centuries, but we still face many challenges. New manufacturing paradigms suggest that we need to make rapid measurements online that relate to the functional performance of the surface. This first 'open questions' collection addresses a subset of the challenges facing the surface metrology community. There are many more challenges which we would like to address in future 'open questions' articles. We welcome your feedback and your suggestions.
Yao, J.; Meemon, P.; Ponting, M.; Rolland, J. P.
Angular scan optical coherence tomography imaging and metrology of spherical gradient refractive index preforms Journal Article
In: Opt. Express, vol. 23, no. 5, pp. 6428-6443, 2015.
Abstract | Links | BibTeX | Tags: related, testing
@article{YAO15a,
title = {Angular scan optical coherence tomography imaging and metrology of spherical gradient refractive index preforms},
author = {Yao, J. and P. Meemon and M. Ponting and J. P. Rolland},
doi = {https://doi.org/10.1364/OE.23.006428},
year = {2015},
date = {2015-03-05},
urldate = {2015-03-05},
journal = {Opt. Express},
volume = {23},
number = {5},
pages = {6428-6443},
abstract = {The fabrication of high-performance spherical gradient refractive index (S-GRIN) optics requires nondestructive metrology techniques to inspect the samples. We have developed an angular-scan, swept-source-based, Fourier-domain optical coherence tomography (OCT) system centered at 1318 nm with 5 mm imaging depth capable of 180° polar scan and 360° azimuthal scan to investigate polymeric S-GRIN preforms. We demonstrate a method that enables simultaneous mapping of the group optical thickness, physical thickness, the radially-averaged group refractive index, and the transmitted wavefront of the S-GRIN preforms. The angular scan OCT imaging and metrology enables direct visualization, molding uniformity characterization, and optical property evaluations of the preforms. The results on two generations of S-GRIN preforms are discussed that showcase the evolution of the manufacturing process in response to the OCT metrology feedback.},
keywords = {related, testing},
pubstate = {published},
tppubtype = {article}
}
The fabrication of high-performance spherical gradient refractive index (S-GRIN) optics requires nondestructive metrology techniques to inspect the samples. We have developed an angular-scan, swept-source-based, Fourier-domain optical coherence tomography (OCT) system centered at 1318 nm with 5 mm imaging depth capable of 180° polar scan and 360° azimuthal scan to investigate polymeric S-GRIN preforms. We demonstrate a method that enables simultaneous mapping of the group optical thickness, physical thickness, the radially-averaged group refractive index, and the transmitted wavefront of the S-GRIN preforms. The angular scan OCT imaging and metrology enables direct visualization, molding uniformity characterization, and optical property evaluations of the preforms. The results on two generations of S-GRIN preforms are discussed that showcase the evolution of the manufacturing process in response to the OCT metrology feedback.