Wednesday, July 31, 2013

1307.7827 (Darin Rosen et al.)

Epoxy-based broadband anti-reflection coating for millimeter-wave optics    [PDF]

Darin Rosen, Aritoki Suzuki, Brian Keating, William Krantz, Adrian T. Lee, Erin Quealy, Paul L. Richards, Praween Siritanasak, William Walker
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.
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