Sidelobe Modeling and Mitigation for a Three Mirror Anastigmat Cosmic Microwave Background Telescope

TL;DR

This paper develops a ray-tracing model to predict and mitigate far-sidelobe contamination in a CMB telescope, proposing a highly scattering surface to significantly reduce systematic errors from wide-angle scattering.

Contribution

It introduces a novel ray-tracing modeling technique for far-sidelobe prediction and proposes a highly scattering surface to reduce sidelobe contamination in CMB telescopes.

Findings

Simulated sidelobe maps match observed patterns.

Highly scattering surface reduces far-sidelobe contrast by over tenfold.

Prototype scattering wall shows promising scattering profile measurements.

Abstract

Telescopes measuring cosmic microwave background (CMB) polarization on large angular scales require exquisite control of systematic errors to ensure the fidelity of the cosmological results. In particular, far-sidelobe contamination from wide angle scattering is a potentially prominent source of systematic error for large aperture microwave telescopes. Here we describe and demonstrate a ray-tracing-based modeling technique to predict far sidelobes for a Three Mirror Anistigmat (TMA) telescope designed to observe the CMB from the South Pole. Those sidelobes are produced by light scattered in the receiver optics subsequently interacting with the walls of the surrounding telescope enclosure. After comparing simulated sidelobe maps and angular power spectra for different enclosure wall treatments, we propose a highly scattering surface that would provide more than an order of magnitude reduction in the degree-scale far-sidelobe contrast compared to a typical reflective surface. We conclude by discussing the fabrication of a prototype scattering wall panel and presenting measurements of its angular scattering profile.