Freeform three-mirror anastigmatic large-aperture telescope and receiver optics for CMB-S4

TL;DR

This paper presents a novel large-aperture freeform three-mirror telescope design with an array of cameras, optimized for the CMB-S4 observatory to enable high-resolution, wide-field cosmic microwave background surveys.

Contribution

It introduces a new large-throughput, large-aperture three-mirror telescope design with an integrated camera array tailored for CMB-S4's delensing survey needs.

Findings

Optical performance meets design specifications.

Mechanical tolerances are within acceptable limits.

Design supports uniform camera distribution across the focal plane.

Abstract

CMB-S4, the next-generation ground-based cosmic microwave background (CMB) observatory, will provide detailed maps of the CMB at millimeter wavelengths to dramatically advance our understanding of the origin and evolution of the universe. CMB-S4 will deploy large and small aperture telescopes with hundreds of thousands of detectors to observe the CMB at arcminute and degree resolutions at millimeter wavelengths. Inflationary science benefits from a deep delensing survey at arcminute resolutions capable of observing a large field of view at millimeter wavelengths. This kind of survey acts as a complement to a degree angular resolution survey. The delensing survey requires a nearly uniform distribution of cameras per frequency band across the focal plane. We present a large-throughput, large-aperture (5-meter diameter) freeform three-mirror anastigmatic telescope and an array of 85 cameras for CMB observations at arcminute resolutions, which meets the needs of the delensing survey of CMB-S4. A detailed prescription of this three-mirror telescope and cameras is provided, with a series of numerical calculations that indicate expected optical performance and mechanical tolerance.