Affiliation
James C. Wyant College of Optical Sciences, University of ArizonaIssue Date
2022Keywords
absolute metrologyoptical metrology
surface metrology
X-ray mirror metrology
X-ray mirrors
X-ray telescope
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Show full item recordPublisher
SPIECitation
Wisniewski, H. J., Arnold, I. J., Heilmann, R. K., Schattenburg, M. L., & Chalifoux, B. D. (2022). Axial shift mapping metrology for X-ray telescope mirrors. Proceedings of SPIE - The International Society for Optical Engineering, 12181.Rights
Copyright © 2022 SPIE.Collection Information
This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.Abstract
The next generation of high-resolution X-ray telescopes will require mirror segments characterized to 5 nm uncertainty or better. This is difficult to achieve due to the mirror segment’s off-axis hyperbolic and parabolic shape and the challenge of manufacturing and testing a cylindrical null lens. In a typical Fizeau interferometer setup, errors in the assumed perfect null lens will be coupled into the final surface figure, increasing uncertainty. To combat the higher uncertainty of the cylindrical null corrector, we have been developing lateral shift mapping, an absolute metrology technique using a Fizeau interferometer. In this technique, the surface under test is laterally shifted between measurements while the reference surface does not move. Contributions to the interferogram due to the surface under test will move, while contributions due to the reference will stay static. Using this information, we can extract the true surface under test with low uncertainty. There is a quadratic ambiguity that arises due to the extraction method being akin to an integration. We have shown in the past our ability to utilize lateral shift mapping to extract flat surfaces to sub-nanometer uncertainties by comparing our results to a three-flat test. We also demonstrated that we can eliminate the quadratic ambiguity in flats using an external measurement with an autocollimator. We are expanding this method from optical flats to cylindrical surfaces, creating axial shift mapping. We will report on progress toward sub-nanometer measurements of cylindrical mirrors using axial shift mapping. © 2022 SPIE. All rights reserved.Note
Immediate accessISSN
0277-786XISBN
9781510653436Version
Final published versionae974a485f413a2113503eed53cd6c53
10.1117/12.2630411
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Lateral shift mapping metrology for X-ray telescope mirrorsWisniewski, H.J.; Whalen, M.M.; Heilmann, R.K.; Schattenburg, M.L.; Chalifoux, B.D.; James C. Wyant College of Optical Sciences, University of Arizona (SPIE, 2021)Currently, high-resolution X-ray telescope mirrors, such as for the Lynx X-Ray Observatory concept, are measured using a Fizeau interferometer with a cylindrical null corrector. Uncertainties in the null wavefront directly couple into the surface measurement uncertainty, including the axial figure and cone angle variation. We extend the absolute surface metrology method of lateral shift mapping for measuring X-ray telescope mirror segments. Lateral shift mapping involves laterally shifting the surface under test relative to the null to multiple positions. The null wavefront can be extracted from the difference between these shifted measurements, leaving only the surface under test. Accurately extracting quadratic terms of the surface under test requires measuring its tilt during shifting. We will show surface metrology results of optical flats measured by Fizeau-based lateral shift mapping with the required angle measured using an autocollimator and compare these results against a three-flat test. We will show how we plan to extend this method to conical X-ray telescope mirror metrology. The lateral shift mapping method reduces the uncertainty introduced by the cylindrical null, a critical step toward making high-resolution X-ray telescope mirrors. © 2021 SPIE.
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Surface Metrology Methods for X-ray Telescope Mirrors, Freeforms, and HeliostatsChalifoux, Brandon D.; Wisniewski, Hayden James; Kim, Daewook; Schattenburg, Mark L. (The University of Arizona., 2023)Modern optical systems require or greatly benefit from freeform or non-rotationally symmetric optics. Increasingly stringent system performance requirements demand high accuracy surface shapes, which drives the need for surface metrology beyond state-of-the-art. This dissertation discusses three projects aimed at filling the need for more accurate or more flexible metrology methods to enable the construction of next generation systems. First is axial shift mapping, a self-referencing metrology technique to measure spaced based X-ray telescope mirrors. X-ray telescopes are composed of nested off-axis parabolic and hyperbolic surfaces, which are difficult to characterize due to their acylindrical shape. I present a shifting Fizeau interferometry technique that decouples contributions from the surface under test in the interferogram from the contributions due to the reference surface. I will present experimental results from using axial shift mapping to characterize a cylindrical mirror. This technique will allow better characterization of X-ray telescope mirrors on the path to a diffraction limited X-ray telescope. Second is the Virtual Ball Probe, an optical profiler being developed at Apre Instruments, Inc. Typically, optical profilers require the probe tip to be normal to the surface. This requires complicated stage geometry and can block certain areas of optics such as steep concave surfaces. The Virtual Ball Probe is designed to measure optical freeforms with surface slopes up to 50 degrees without the need for tilting of the probe tip to be normal with the surface. This allows for simple stage geometry and can accurately measure steep internal optical surfaces. I will discuss the system design and show current system performance. This system fills the need for an accurate yet flexible metrology system for modern freeform optics. Third is Grating Embedded Mirrors for single shot heliostat optical metrology. Commercial concentrated solar power plants are required to accurately monitor the surface slope error and canting error of thousands of heliostats to maintain plant efficiency. We have fabricated test Grating Embedded Mirrors (GEMs), which are float glass mirrors with phase gratings written into the bulk glass using an ultra-fast laser. We use these gratings to direct light to non-specular directions. I placed these grating embedded mirrors in front of a metrology system dubbed Diffractive Auto-Stigmatic Hartmann Camera (DASHCam) to measure the mirror surface slope error. I will compare the results gathered by DASHCam to the surface slope error as measured by a Fizeau Interferometer. GEM’s flexibility of design and ease of measurement is aimed at providing a compact, accurate, and high-speed heliostat slope error metrology system that is robust to harsh environmental conditions for the next generation of concentrated solar power plants. Together, these metrology systems advance the state-of-the-art by increasing flexibility while lowering uncertainty to meet the increasingly stringent requirements of next generation systems.
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In-process metrology for segmented optics UV curing controlChoi, Heejoo; Esparza, Marcos; Lamdan, Ariel; Feng, Yi-Ting; Milster, Tom; Apai, Daniel; Kim, Dae Wook; Univ Arizona, Wyant Coll Opt Sci; Univ Arizona, Large Binocular Telescope Observ; Univ Arizona, Dept Astron & Steward Observ; et al. (SPIE-INT SOC OPTICAL ENGINEERING, 2020-08-20)Powerful and novel telescope design is key to pushing the available limits of astronomical sciences and a segmented primary is an attractive approach. For the Nautilus Space mission, a segmented lens has been proposed to replace large monolithic primary optics for the purpose of survey faint objects like exo-planets as well as time-domain astrophysics observations. Enabling technology for Nautilus is an ultra-lightweight multi-order diffractive engineered (MODE) lens that replaces bulky primary mirrors. The MODE lens consists of multiple, identical, molded segments. This is because the complicated optical design of both the diffractive surfaces is not easily manufacturable by traditional fabrication methods. Besides, the molding approach for identical segmented optics allows for a cost-efficient process. Conversely, the fusion of segmented optics demands high precision metrology and a delicate assembly strategy. We propose an in-process metrology technique that mitigates post-assembly process complications. This system monitors the co-phase character of the segmented optics during UV cured assembly, guiding the overall process.