Aerogel scattering filters for cosmic microwave background observations

TL;DR

This paper introduces broadband, tunable infrared-blocking filters using aerogel with embedded scattering particles, suitable for large-aperture cryogenic receivers in cosmic microwave background experiments.

Contribution

It presents a novel aerogel-based filter design with tunable cutoff frequencies and no need for anti-reflection coatings, optimized for CMB observations.

Findings

Achieved broadband operation from DC to above 1 THz.

Demonstrated scalable production of 40-cm diameter filters.

Enabled large-aperture cryogenic receiver applications.

Abstract

We present the design and performance of broadband and tunable infrared-blocking filters for millimeter and sub-millimeter astronomy composed of small scattering particles embedded in an aerogel substrate. The ultra-low-density (typically < 150 mg/cm^3) aerogel substrate provides an index of refraction as low as 1.05, removing the need for anti-reflection coatings and allowing for broadband operation from DC to above 1 THz. The size distribution of the scattering particles can be tuned to provide a variable cutoff frequency. Aerogel filters with embedded high-resistivity silicon powder are being produced at 40-cm diameter to enable large-aperture cryogenic receivers for cosmic microwave background polarimeters, which require large arrays of sub-Kelvin detectors in their search for the signature of an inflationary gravitational-wave background.