Broadband anti-reflective coatings for cosmic microwave background experiments

Conference · Mon Jan 01 00:00:00 EST 2018

DOI:https://doi.org/10.1117/12.2315674· OSTI ID:1481266

Nadolski, A.; Kofman, A. M.; Vieira, J. D.; Ade, P. A. R.; Ahmed, Z.; Anderson, A. J.; Avva, J. S.; Basu Thakur, R.; Bender, A. N.; Benson, B. A.; Carlstrom, J. E.; Carter, F. W.; Cecil, T. W.; Chang, C. L.; Ding, J.; Harke-Hosemann, A. H.; Khaire, T. S.; Kuhlmann, S.; Novosad, V.; Pearson, J. ; Posada, C. M.; Wang, G.; Yefremenko, V.

The desire for higher sensitivity has driven ground-based cosmic microwave background (CMB) experiments to employ ever larger focal planes, which in turn require larger reimaging optics. Practical limits to the maximum size of these optics motivates the development of quasi-optically-coupled (lenslet-coupled), multi-chroic detectors. These detectors can be sensitive across a broader bandwidth compared to waveguide-coupled detectors. However, the increase in bandwidth comes at a cost: the lenses (up to ~700 mm diameter) and lenslets (~5 mm diameter, hemispherical lenses on the focal plane) used in these systems are made from high-refractive-index materials (such as silicon or amorphous aluminum oxide) that reflect nearly a third of the incident radiation. In order to maximize the faint CMB signal that reaches the detectors, the lenses and lenslets must be coated with an anti-reflective (AR) material. The AR coating must maximize radiation transmission in scientifically interesting bands and be cryogenically stable. Such a coating was developed for the third generation camera, SPT-3G, of the South Pole Telescope (SPT) experiment, but the materials and techniques used in the development are general to AR coatings for mm-wave optics. The three-layer polytetra uoroethylene-based AR coating is broadband, inexpensive, and can be manufactured with simple tools. The coating is field tested; AR coated focal plane elements were deployed in the 2016-2017 austral summer and AR coated reimaging optics were deployed in 2017-2018.

• Research Organization: Argonne National Laboratory (ANL), Argonne, IL (United States)
• Sponsoring Organization: Alfred P. Sloan Foundation; USDOE Office of Science - Office of High Energy Physics; National Science Foundation (NSF); Gordon and Betty Moore Foundation
• DOE Contract Number: AC02-06CH11357
• OSTI ID: 1481266
• Resource Relation: Conference: 2018 SPIE Astronomical Telescopes and Instrumentation, 06/10/18 - 06/15/18, Austin, TX, US
• Country of Publication: United States
• Language: English

Related Subjects

anti-reflective coating
broadband
millimeter-wave