Publications by Gautam Gunjala
2023
Gautam Gunjala; Antoine Wojdyla; Kenneth A. Goldberg; Zhi Qiao; Xianbo Shi; Lahsen Assoufid; Laura Waller
Data-driven modeling and control of an X-ray bimorph adaptive mirror Journal Article
In: Journal of Synchrotron Radiation, vol. 30, no. 1, 2023.
@article{Gunjala:tv5041,
title = {Data-driven modeling and control of an X-ray bimorph adaptive mirror},
author = {Gautam Gunjala and Antoine Wojdyla and Kenneth A. Goldberg and Zhi Qiao and Xianbo Shi and Lahsen Assoufid and Laura Waller},
url = {https://doi.org/10.1107/S1600577522011080},
doi = {10.1107/S1600577522011080},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
journal = {Journal of Synchrotron Radiation},
volume = {30},
number = {1},
abstract = {Adaptive X-ray mirrors are being adopted on high-coherent-flux synchrotron and X-ray free-electron laser beamlines where dynamic phase control and aberration compensation are necessary to preserve wavefront quality from source to sample, yet challenging to achieve. Additional difficulties arise from the inability to continuously probe the wavefront in this context, which demands methods of control that require little to no feedback. In this work, a data-driven approach to the control of adaptive X-ray optics with piezo-bimorph actuators is demonstrated. This approach approximates the non-linear system dynamics with a discrete-time model using random mirror shapes and interferometric measurements as training data. For mirrors of this type, prior states and voltage inputs affect the shape-change trajectory, and therefore must be included in the model. Without the need for assumed physical models of the mirror's behavior, the generality of the neural network structure accommodates drift, creep and hysteresis, and enables a control algorithm that achieves shape control and stability below 2nm RMS. Using a prototype mirror and it ex situ metrology, it is shown that the accuracy of our trained model enables open-loop shape control across a diverse set of states and that the control algorithm achieves shape error magnitudes that fall within diffraction-limited performance.},
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Adaptive X-ray mirrors are being adopted on high-coherent-flux synchrotron and X-ray free-electron laser beamlines where dynamic phase control and aberration compensation are necessary to preserve wavefront quality from source to sample, yet challenging to achieve. Additional difficulties arise from the inability to continuously probe the wavefront in this context, which demands methods of control that require little to no feedback. In this work, a data-driven approach to the control of adaptive X-ray optics with piezo-bimorph actuators is demonstrated. This approach approximates the non-linear system dynamics with a discrete-time model using random mirror shapes and interferometric measurements as training data. For mirrors of this type, prior states and voltage inputs affect the shape-change trajectory, and therefore must be included in the model. Without the need for assumed physical models of the mirror's behavior, the generality of the neural network structure accommodates drift, creep and hysteresis, and enables a control algorithm that achieves shape control and stability below 2nm RMS. Using a prototype mirror and it ex situ metrology, it is shown that the accuracy of our trained model enables open-loop shape control across a diverse set of states and that the control algorithm achieves shape error magnitudes that fall within diffraction-limited performance.
Eric Li; Stuart Sherwin; Gautam Gunjala; Laura Waller
Exceeding the limits of algorithmic self-calibrated aberration recovery in Fourier ptychography Journal Article
In: Opt. Continuum, vol. 2, no. 1, pp. 119–130, 2023.
@article{Li:23,
title = {Exceeding the limits of algorithmic self-calibrated aberration recovery in Fourier ptychography},
author = {Eric Li and Stuart Sherwin and Gautam Gunjala and Laura Waller},
url = {https://opg.optica.org/optcon/abstract.cfm?URI=optcon-2-1-119},
doi = {10.1364/OPTCON.475990},
year = {2023},
date = {2023-01-01},
journal = {Opt. Continuum},
volume = {2},
number = {1},
pages = {119--130},
publisher = {Optica Publishing Group},
abstract = {Fourier ptychographic microscopy is a computational imaging technique that provides quantitative phase information and high resolution over a large field-of-view. Although the technique presents numerous advantages over conventional microscopy, model mismatch due to unknown optical aberrations can significantly limit reconstruction quality. A practical way of correcting for aberrations without additional data capture is through algorithmic self-calibration, in which a pupil recovery step is embedded into the reconstruction algorithm. However, software-only aberration correction is limited in accuracy. Here, we evaluate the merits of implementing a simple, dedicated calibration procedure for applications requiring high accuracy. In simulations, we find that for a target sample reconstruction error, we can image without any aberration corrections only up to a maximum aberration magnitude of $łambda$/40. When we use algorithmic self-calibration, we can tolerate an aberration magnitude up to $łambda$/10 and with our proposed diffuser calibration technique, this working range is extended further to $łambda$/3. Hence, one can trade off complexity for accuracy by using a separate calibration process, which is particularly useful for larger aberrations.},
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pubstate = {published},
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Fourier ptychographic microscopy is a computational imaging technique that provides quantitative phase information and high resolution over a large field-of-view. Although the technique presents numerous advantages over conventional microscopy, model mismatch due to unknown optical aberrations can significantly limit reconstruction quality. A practical way of correcting for aberrations without additional data capture is through algorithmic self-calibration, in which a pupil recovery step is embedded into the reconstruction algorithm. However, software-only aberration correction is limited in accuracy. Here, we evaluate the merits of implementing a simple, dedicated calibration procedure for applications requiring high accuracy. In simulations, we find that for a target sample reconstruction error, we can image without any aberration corrections only up to a maximum aberration magnitude of $łambda$/40. When we use algorithmic self-calibration, we can tolerate an aberration magnitude up to $łambda$/10 and with our proposed diffuser calibration technique, this working range is extended further to $łambda$/3. Hence, one can trade off complexity for accuracy by using a separate calibration process, which is particularly useful for larger aberrations.
2022
Gautam Gunjala
Towards diffraction-limited short-wavelength imaging systems PhD Thesis
EECS Department, University of California, Berkeley, 2022.
@phdthesis{Gunjala:EECS-2022-117,
title = {Towards diffraction-limited short-wavelength imaging systems},
author = {Gautam Gunjala},
url = {http://www2.eecs.berkeley.edu/Pubs/TechRpts/2022/EECS-2022-117.html},
year = {2022},
date = {2022-05-01},
urldate = {2022-05-01},
number = {UCB/EECS-2022-117},
school = {EECS Department, University of California, Berkeley},
abstract = {Modern applications of optics, especially those which require shorter wavelengths of light, place ever-increasing demands on the performance of optical tools and systems. Working with extreme ultraviolet, soft x-ray and hard x-ray light poses complex limitations and challenges to diagnosing and maintaining diffraction-limited performance by measuring and controlling optical aberrations. By utilizing computational methods such as optimization and machine learning, we show that some of these limitations can be circumvented without sacrificing accuracy or precision.
In this work, we discuss a method for aberration measurement that is based on an analysis of speckle images acquired in situ. By using a stationary random object, our method eliminates the need for precise manufacturing and alignment of a test target. Moreover, the method provides a full, dense characterization of the optical system under test using relatively few images. The method has been successfully applied to an EUV microscope system, and is shown to be accurate to within λ/180. We also discuss a method for aberration compensation via the characterization and control of an adaptive optical element for x-ray optical systems. Adaptive x-ray optics are a relatively new technology, and our work aims to enable their use within the specifications of synchrotron beamline systems. To this end, we demonstrate the ability to experimentally predict and control the behavior of the glancing-incidence deformable mirror surface to within 2 nm rms, allowing the application of sub-wavelength corrections to an incident wavefront.},
keywords = {},
pubstate = {published},
tppubtype = {phdthesis}
}
Modern applications of optics, especially those which require shorter wavelengths of light, place ever-increasing demands on the performance of optical tools and systems. Working with extreme ultraviolet, soft x-ray and hard x-ray light poses complex limitations and challenges to diagnosing and maintaining diffraction-limited performance by measuring and controlling optical aberrations. By utilizing computational methods such as optimization and machine learning, we show that some of these limitations can be circumvented without sacrificing accuracy or precision.
In this work, we discuss a method for aberration measurement that is based on an analysis of speckle images acquired in situ. By using a stationary random object, our method eliminates the need for precise manufacturing and alignment of a test target. Moreover, the method provides a full, dense characterization of the optical system under test using relatively few images. The method has been successfully applied to an EUV microscope system, and is shown to be accurate to within λ/180. We also discuss a method for aberration compensation via the characterization and control of an adaptive optical element for x-ray optical systems. Adaptive x-ray optics are a relatively new technology, and our work aims to enable their use within the specifications of synchrotron beamline systems. To this end, we demonstrate the ability to experimentally predict and control the behavior of the glancing-incidence deformable mirror surface to within 2 nm rms, allowing the application of sub-wavelength corrections to an incident wavefront.
In this work, we discuss a method for aberration measurement that is based on an analysis of speckle images acquired in situ. By using a stationary random object, our method eliminates the need for precise manufacturing and alignment of a test target. Moreover, the method provides a full, dense characterization of the optical system under test using relatively few images. The method has been successfully applied to an EUV microscope system, and is shown to be accurate to within λ/180. We also discuss a method for aberration compensation via the characterization and control of an adaptive optical element for x-ray optical systems. Adaptive x-ray optics are a relatively new technology, and our work aims to enable their use within the specifications of synchrotron beamline systems. To this end, we demonstrate the ability to experimentally predict and control the behavior of the glancing-incidence deformable mirror surface to within 2 nm rms, allowing the application of sub-wavelength corrections to an incident wavefront.
2020
Gautam Gunjala; Antoine Wojdyla; Stuart Sherwin; Aamod Shanker; Markus P. Benk; Kenneth A. Goldberg; Patrick P. Naulleau; Laura Waller
Extreme ultraviolet microscope characterization using photomask surface roughness Journal Article
In: Scientific Reports, vol. 10, no. 1, pp. 11673, 2020.
@article{gunjala2020extreme,
title = {Extreme ultraviolet microscope characterization using photomask surface roughness },
author = {Gautam Gunjala and Antoine Wojdyla and Stuart Sherwin and Aamod Shanker and Markus P. Benk and Kenneth A. Goldberg and Patrick P. Naulleau and Laura Waller },
url = {https://doi.org/10.1038/s41598-020-68588-w},
doi = {10.1038/s41598-020-68588-w},
year = {2020},
date = {2020-07-15},
journal = {Scientific Reports},
volume = {10},
number = {1},
pages = {11673},
keywords = {},
pubstate = {published},
tppubtype = {article}
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2018
Gautam Gunjala; Stuart Sherwin; Aamod Shanker; Laura Waller
Aberration recovery by imaging a weak diffuser Journal Article
In: Optics express, vol. 26, no. 16, pp. 21054–21068, 2018.
@article{gunjala2018aberration,
title = {Aberration recovery by imaging a weak diffuser},
author = { Gautam Gunjala and Stuart Sherwin and Aamod Shanker and Laura Waller},
url = {https://doi.org/10.1364/OE.26.021054},
doi = {10.1364/OE.26.021054},
year = {2018},
date = {2018-08-06},
journal = {Optics express},
volume = {26},
number = {16},
pages = {21054--21068},
publisher = {Optical Society of America},
keywords = {},
pubstate = {published},
tppubtype = {article}
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Gautam Gunjala; Antoine Wojdyla; Aamod Shanker; Stuart Sherwin; Markus P Benk; Kenneth A Goldberg; Patrick P Naulleau; Laura Waller
Field-varying aberration recovery in EUV microscopy using mask roughness Inproceedings
In: Computational Optical Sensing and Imaging, pp. CW2E–2, Optical Society of America 2018.
@inproceedings{gunjala2018field,
title = {Field-varying aberration recovery in EUV microscopy using mask roughness},
author = { Gautam Gunjala and Antoine Wojdyla and Aamod Shanker and Stuart Sherwin and Markus P Benk and Kenneth A Goldberg and Patrick P Naulleau and Laura Waller},
url = {https://www.osapublishing.org/abstract.cfm?uri=COSI-2018-CW2E.2},
year = {2018},
date = {2018-06-25},
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Aamod Shanker; Laura Waller; Gautam Gunjala; Antoine Wojdyla; Dmitriy Voronov; Patrick P Naulleau
Speckle metrology for extreme ultra-violet lithography Inproceedings
In: Extreme Ultraviolet (EUV) Lithography IX, pp. 105830T, International Society for Optics and Photonics 2018.
@inproceedings{shanker2018speckle,
title = {Speckle metrology for extreme ultra-violet lithography},
author = { Aamod Shanker and Laura Waller and Gautam Gunjala and Antoine Wojdyla and Dmitriy Voronov and Patrick P Naulleau},
url = {https://doi.org/10.1117/12.2299605},
doi = {10.1117/12.2299605},
year = {2018},
date = {2018-06-01},
booktitle = {Extreme Ultraviolet (EUV) Lithography IX},
volume = {10583},
pages = {105830T},
organization = {International Society for Optics and Photonics},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
2016
Aamod Shanker; Antoine Wojdyla; Gautam Gunjala; Jonathan Dong; Markus P Benk; Andrew R Neureuther; Kenneth A Goldberg; Laura Waller
Off-axis aberration estimation in an EUV microscope using natural speckle Inproceedings
In: Imaging Systems and Applications, pp. ITh1F–2, Optical Society of America 2016.
@inproceedings{shanker2016off,
title = {Off-axis aberration estimation in an EUV microscope using natural speckle},
author = { Aamod Shanker and Antoine Wojdyla and Gautam Gunjala and Jonathan Dong and Markus P Benk and Andrew R Neureuther and Kenneth A Goldberg and Laura Waller},
url = {https://www.osapublishing.org/abstract.cfm?uri=ISA-2016-ITh1F.2},
year = {2016},
date = {2016-07-25},
booktitle = {Imaging Systems and Applications},
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organization = {Optical Society of America},
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Gautam Gunjala; Aamod Shanker; Volker Jaedicke; Nick Antipa; Laura Waller
Optical transfer function characterization using a weak diffuser Inproceedings
In: Three-Dimensional and Multidimensional Microscopy: Image Acquisition and Processing XXIII, pp. 971315, International Society for Optics and Photonics 2016.
@inproceedings{gunjala2016optical,
title = {Optical transfer function characterization using a weak diffuser},
author = { Gautam Gunjala and Aamod Shanker and Volker Jaedicke and Nick Antipa and Laura Waller},
url = {https://www.spiedigitallibrary.org/conference-proceedings-of-spie/9713/1/Optical-transfer-function-characterization-using-a-weak-diffuser/10.1117/12.2213271.short?SSO=1},
year = {2016},
date = {2016-03-25},
booktitle = {Three-Dimensional and Multidimensional Microscopy: Image Acquisition and Processing XXIII},
volume = {9713},
pages = {971315},
organization = {International Society for Optics and Photonics},
keywords = {},
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2015
Zachary F Phillips; Gautam Gunjala; Paroma Varma; Jingshan Zhong; Laura Waller
Design of a Domed LED Illuminator for High-Angle Computational Illumination Inproceedings
In: Imaging Systems and Applications, pp. ITh1A–2, Optical Society of America 2015.
@inproceedings{phillips2015design,
title = {Design of a Domed LED Illuminator for High-Angle Computational Illumination},
author = { Zachary F Phillips and Gautam Gunjala and Paroma Varma and Jingshan Zhong and Laura Waller},
url = {https://www.osapublishing.org/abstract.cfm?uri=isa-2015-ITh1A.2},
year = {2015},
date = {2015-06-07},
booktitle = {Imaging Systems and Applications},
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organization = {Optical Society of America},
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pubstate = {published},
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