BICEP/Keck. XIX. Extremely thin composite polymer vacuum windows for BICEP and other high-throughput millimeter-wave telescopes

Ade, P. A. R. ORCID: https://orcid.org/0000-0002-5127-0401, Ahmed, Z., Amiri, M., Barkats, D., Basu Thakur, R., Sudiwala, R. ORCID: https://orcid.org/0000-0003-3240-5304 and Tucker, Carole ORCID: https://orcid.org/0000-0002-1851-3918 2026. BICEP/Keck. XIX. Extremely thin composite polymer vacuum windows for BICEP and other high-throughput millimeter-wave telescopes. The Astrophysical Journal 1000 (2) , 238. 10.3847/1538-4357/ae486d

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Abstract

Millimeter-wave refracting telescopes targeting the degree-scale structure of the cosmic microwave background (CMB) have recently grown to diffraction-limited apertures of over 0.5 m. These instruments are entirely housed in vacuum cryostats to support their subkelvin bolometric detectors and to minimize radiative loading from thermal emission due to absorption loss in their transmissive optical elements. The large vacuum window is the only optical element in the system at ambient temperature, and therefore minimizing loss in the window is crucial for maximizing detector sensitivity. This motivates the use of low-loss polymer materials and a window as thin as practicable. However, the window must simultaneously meet the requirement to keep a sufficient vacuum, and therefore must limit gas permeation and remain mechanically robust against catastrophic failure under pressure. We report on the development of extremely thin composite polyethylene window technology that meets these goals. Two windows have been deployed for two full observing seasons on the BICEP3 and the 150 GHz BICEP Array receiver CMB telescopes at the South Pole. On BICEP3, the window has demonstrated a 6% improvement in detector sensitivity.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Schools > Physics and Astronomy
Additional Information:	Full list of authors can be seen here - https://doi.org/10.3847/1538-4357/ae486d License information from Publisher: LICENSE 1: URL: https://creativecommons.org/licenses/by/4.0/, Type: cc-by
Publisher:	American Astronomical Society
ISSN:	0004-637X
Date of First Compliant Deposit:	2 April 2026
Date of Acceptance:	18 February 2026
Last Modified:	02 Aug 2026 10:21
URI:	https://orca.cardiff.ac.uk/id/eprint/186143

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