From Event: SPIE Astronomical Telescopes + Instrumentation, 2018
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 ultralow-density (< 100 mg/cm3) 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.
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Thomas Essinger-Hileman, Charles L. Bennett, Lance Corbett, Haiquan Guo, Tobias Marriage, Mary Ann B. Meador, Karwan Rostem, and Edward J. Wollack, "Aerogel scattering filters for cosmic microwave background observations," Proc. SPIE 10708, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy IX, 107080F (Presented at SPIE Astronomical Telescopes + Instrumentation: June 12, 2018; Published: 9 July 2018); https://doi.org/10.1117/12.2313387.