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arXiv · 2505.11118

Prototype sub-wavelength structure anti-reflection coating on alumina filters for ground-based CMB telescopes

Kosuke Aizawa·Ryosuke Akizawa·Scott Cray·Shaul Hanany·Shotaro Kawano·Jürgen Koch·Kuniaki Konishi·Rex Lam·Tomotake Matsumura·Haruyuki Sakurai·Ryota Takaku
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Abstract

We present designs and fabrication of sub-wavelength anti-reflection (AR) structures on alumina for infrared absorptive filters with passbands near 30, 125, and 250 GHz. These bands are widely used by ground-based instruments measuring the cosmic microwave background radiation. The designs are tuned to provide reflectance of 2% or less for fractional bandwidths between 51% and 72%, with each of the three primary bands containing two sub-bands. We make the sub-wavelength structures (SWS), which resemble a two-dimensional array of pyramids, using laser ablation. We measure the shapes of the fabricated pyramids and show that for incidence angles up to 20 degrees the predicted in-band average reflectance is 2% or less, in agreement with the design. The band average instrumental polarization is less than $3\times 10^{-3}$.

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Kosuke Aizawa, Ryosuke Akizawa, Scott Cray, Shaul Hanany, Shotaro Kawano, Jürgen Koch, Kuniaki Konishi, Rex Lam, Tomotake Matsumura, Haruyuki Sakurai, Ryota Takaku. 2025-05-16. Prototype sub-wavelength structure anti-reflection coating on alumina filters for ground-based CMB telescopes. https://arxiv.org/abs/2505.11118

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