Epoxy-based broadband anti-reflection coating for millimeter-wave optics

TL;DR

This paper presents the development of epoxy-based broadband anti-reflection coatings for millimeter-wave optics, achieving low reflection and absorption losses over wide bandwidths suitable for cryogenic astrophysics experiments.

Contribution

The authors introduce multi-layer epoxy coatings with tunable dielectric constants that significantly reduce reflection and absorption in millimeter-wave optics at cryogenic temperatures.

Findings

Reflection suppressed to 10% over 92% and 104% bandwidths with two- and three-layer coatings.

Dielectric constants tuned between 2.06 and 7.44 using epoxy mixtures.

Absorption loss below 1% at 140 K for two-layer coating.

Abstract

We have developed epoxy-based, broadband anti-reflection coatings for millimeter-wave astrophysics experiments with cryogenic optics. By using multiple-layer coatings where each layer steps in dielectric constant, we achieved low reflection over a wide bandwidth. We suppressed the reflection from an alumina disk to 10% over fractional bandwidths of 92% and 104% using two-layer and three-layer coatings, respectively. The dielectric constants of epoxies were tuned between 2.06 and 7.44 by mixing three types of epoxy and doping with strontium titanate powder required for the high dielectric mixtures. At 140 Kelvin, the band-integrated absorption loss in the coatings was suppressed to less than 1% for the two-layer coating, and below 10% for the three-layer coating.