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Proceedings Paper

Far sidelobes from baffles and telescope support structures in the Atacama Cosmology Telescope
Author(s): Patricio A. Gallardo; Nicholas F. Cothard; Roberto Puddu; Rolando Dünner; Brian J. Koopman; Michael D. Niemack; Sara M. Simon; Edward J. Wollack
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Paper Abstract

The Atacama Cosmology Telescope (ACT) is a 6 m telescope located in the Atacama Desert, designed to measure the cosmic microwave background (CMB) with arcminute resolution. ACT, with its third generation polarization sensitive array, Advanced ACTPol, is being used to measure the anisotropies of the CMB in five frequency bands in large areas of the sky (~ 15,000 deg2). These measurements are designed to characterize the large scale structure of the universe, test cosmological models and constrain the sum of the neutrino masses. As the sensitivity of these wide surveys increases, the control and validation of the far sidelobe response becomes increasingly important and is particularly challenging as multiple reflections, spillover, diffraction and scattering become difficult to model and characterize at the required levels. In this work, we present a ray trace model of the ACT upper structure which is used to describe much of the observed far sidelobe pattern. This model combines secondary mirror spillover measurements with a 3D CAD model based on photogrammetry measurements to simulate the beam of the camera and the comoving ground shield. This simulation shows qualitative agreement with physical optics tools and features observed in far sidelobe measurements. We present this method as an efficient first-order calculation that, although it does not capture all diffraction effects, informs interactions between the structural components of the telescope and the optical path, which can then be combined with more computationally intensive physical optics calculations. This method can be used to predict sidelobe patterns in the design stage of future optical systems such as the Simons Observatory, CCAT-prime, and CMB Stage IV.

Paper Details

Date Published: 15 August 2018
PDF: 10 pages
Proc. SPIE 10708, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy IX, 107082L (15 August 2018); doi: 10.1117/12.2313005
Show Author Affiliations
Patricio A. Gallardo, Cornell Univ. (United States)
Nicholas F. Cothard, Cornell Univ. (United States)
Roberto Puddu, Pontificia Univ. Católica de Chile (Chile)
Rolando Dünner, Pontificia Univ. Católica de Chile (Chile)
Brian J. Koopman, Cornell Univ. (United States)
Michael D. Niemack, Cornell Univ. (United States)
Sara M. Simon, Univ. of Michigan (United States)
Edward J. Wollack, NASA Goddard Space Flight Ctr. (United States)

Published in SPIE Proceedings Vol. 10708:
Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy IX
Jonas Zmuidzinas; Jian-Rong Gao, Editor(s)

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