2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/194111The Atacama Cosmology Telescope is a 6-meter telescope designed to map the Cosmic Microwave Background simultaneously at 145 GHz, 215 GHz, and 280 GHz with arcminute resolution. Each frequency will have a 32 by 32 element focal plane array of TES bolometers. This paper describes the design of the telescope and the cold reimaging optics, which is optimized for millimeter-wave observations with these sensitive detectors.23 pages. Accepted for publication in Applied Optics. Several minor clarifications added after peer reviewAstrophysicstext