SPT-3G secondary mirror geometry

• Main Author: Stark, Antony A.
• Format: Report
• Language: unknown
• Published: arXiv 2018
• Subjects: Instrumentation and Methods for Astrophysics astro-ph.IM; FOS Physical sciences; 78A05, 85A40; South Pole; South pole
• Online Access: https://dx.doi.org/10.48550/arxiv.1809.08212; https://arxiv.org/abs/1809.08212

SPT-3G is a detector system for the 10m diameter South Pole Telescope, comprising 16,000 millimeter-wave bolometers. It is used for a deep Cosmic Microwave Background survey of the Southern sky. This paper describes the geometry of the secondary mirror, which is a section of a prolate spheroid, in several useful coordinate systems. There is application to off-axis mirrors in general. A geometric theorem is proven, relating to the Dragone condition: the intersection of a prolate spheroid and any plane is an ellipse; the lines connecting points on that ellipse to either focus compose a right circular cone; the central axes of the two cones from the two foci intersect outside the interior of the spheroid. : 34 pages, 1 figure, C program