Design and Fabrication of Metamaterial Anti-Reflection Coatings for the Simons Observatory

TL;DR

This paper presents the design and fabrication of broadband metamaterial anti-reflection coatings for large silicon optics used in the Simons Observatory's CMB survey, enhancing optical performance.

Contribution

It introduces mechanically robust, highly efficient metamaterial AR coatings with octave bandwidth for large silicon lenses in CMB telescopes, including fabrication methods and performance evaluation.

Findings

Achieved octave bandwidth AR coatings for silicon optics up to 46 cm diameter.

Demonstrated high transparency and efficiency of the coatings across multiple frequency bands.

Discussed potential extension to harder optical materials like alumina.

Abstract

The Simons Observatory (SO) will be a cosmic microwave background (CMB) survey experiment with three small-aperture telescopes and one large-aperture telescope, which will observe from the Atacama Desert in Chile. In total, SO will field over 60,000 transition-edge sensor (TES) bolometers in six spectral bands centered between 27 and 280 GHz in order to achieve the sensitivity necessary to measure or constrain numerous cosmological quantities, as outlined in The Simons Observatory Collaboration et al. (2019). These telescopes require 33 highly transparent, large aperture, refracting optics. To this end, we developed mechanically robust, highly efficient, metamaterial anti-reflection (AR) coatings with octave bandwidth coverage for silicon optics up to 46 cm in diameter for the 22-55, 75-165, and 190-310 GHz bands. We detail the design, the manufacturing approach to fabricate the SO lenses, their performance, and possible extensions of metamaterial AR coatings to optical elements made of harder materials such as alumina.