The optical design of the six-meter CCAT-prime and Simons Observatory telescopes

TL;DR

This paper presents a unified optical design for 6-meter crossed-Dragone telescopes used in submillimeter and millimeter astronomy, emphasizing high throughput, flat focal plane, and polarization purity.

Contribution

It introduces a common optical design approach for two major telescopes, optimizing aberration correction and polarization for high-altitude astronomical observations.

Findings

Design achieves a 7.8-degree field of view at 3 mm wavelengths

Optics suppress first-order astigmatism and maintain polarization purity

Design allows illumination of over 100,000 diffraction-limited beams at <1 mm wavelengths

Abstract

A common optical design for a coma-corrected, 6-meter aperture, crossed-Dragone telescope has been adopted for the CCAT-prime telescope of CCAT Observatory, Inc., and for the Large Aperture Telescope of the Simons Observatory. Both are to be built in the high altitude Atacama Desert in Chile for submillimeter and millimeter wavelength observations, respectively. The design delivers a high throughput, relatively flat focal plane, with a field of view 7.8 degrees in diameter for 3 mm wavelengths, and the ability to illuminate >100k diffraction-limited beams for < 1 mm wavelengths. The optics consist of offset reflecting primary and secondary surfaces arranged in such a way as to satisfy the Mizuguchi-Dragone criterion, suppressing first-order astigmatism and maintaining high polarization purity. The surface shapes are perturbed from their standard conic forms in order to correct coma aberrations. We discuss the optical design, performance, and tolerancing sensitivity. More information about CCAT-prime can be found at ccatobservatory.org and about Simons Observatory at simonsobservatory.org.