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Title: Broadband anti-reflective coatings for cosmic microwave background experiments

Abstract

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 coatingmore » 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.« less

Authors:
;
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States); Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
Contributing Org.:
SPT
OSTI Identifier:
1478058
Report Number(s):
arXiv:1809.00030; FERMILAB-CONF-18-447-AE
1682457
DOE Contract Number:  
AC02-07CH11359
Resource Type:
Conference
Journal Name:
Proc.SPIE Int.Soc.Opt.Eng.
Additional Journal Information:
Journal Volume: 10708; Conference: SPIE Astronomical Telescopes + Instrumentation 2018, Austin, USA, 06/10-06/15/2018
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; 46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY

Citation Formats

Nadolski, A., and et al. Broadband anti-reflective coatings for cosmic microwave background experiments. United States: N. p., 2018. Web. doi:10.1117/12.2315674.
Nadolski, A., & et al. Broadband anti-reflective coatings for cosmic microwave background experiments. United States. doi:10.1117/12.2315674.
Nadolski, A., and et al. Mon . "Broadband anti-reflective coatings for cosmic microwave background experiments". United States. doi:10.1117/12.2315674. https://www.osti.gov/servlets/purl/1478058.
@article{osti_1478058,
title = {Broadband anti-reflective coatings for cosmic microwave background experiments},
author = {Nadolski, A. and et al.},
abstractNote = {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.},
doi = {10.1117/12.2315674},
journal = {Proc.SPIE Int.Soc.Opt.Eng.},
number = ,
volume = 10708,
place = {United States},
year = {2018},
month = {7}
}

Conference:
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