Record Details

Mirror Illumination and Spillover Measurements of the Atacama Cosmology Telescope
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Author and Affiliation:
Gallardo, Patricio(Pontificia Univ. Catolica de Chile, Facultad de Fisica, Santiago, Chile);
Dunner, Rolando(Pontificia Univ. Catolica de Chile, Facultad de Fisica, Santiago, Chile);
Wollack, Ed(NASA Goddard Space Flight Center, Greenbelt, MD, United States);
Jerez-Hanckes, Carlos(Pontificia Univ. Catolica de Chile, Santiago, Chile)
Abstract: The Atacama Cosmology Telescope (ACT) is a 6 m telescope designed to map the Cosmic Microwave Background (CMB) simultaneously at 145 GHz, 220GHz and 280GHz, The receiver in ACT, the Millimeter Bolometer Array Camera, features 1000 TES bolometers in each band, The detector performance depends critically on the total optical loading, requiring the spmover contributions from the optics to be minimal. This inspired the use of a cold Lyot stop to limit the illumination of the primary and the use of guard rings surrounding the primary and secondary reflectors. Here, we present a direct measurement of the illumination aperture for both reflectors and of the attenuation level outside the main optical path. We used a 145 GHz, 1 m W source and a chopper wheel to produce a time-varying signal with a broad heam proflle, We sampled the response of the camera for different locations of the source, placed in front and beside the primary and secondary mirrors. The aperture of the primary was measured to be 5,72 plus or minus 0,17m in diameter (95 plus or minus 3% of its geometrical size), while the aperture of the secondary yielded 2 plus or minus 0.12m in diameter. Both apertures are consistent with the optical design. Comparing to previous measurements of the beam solid angle from planet observations, we estimate an optical efficiency of 72.3 plus or minus 4,8%. We found that the attenuation outside the primary aperture was -16 plus or minus 2dB, which is below the theoretical expectations, and -22 plus or minus 1 dB outside the secondary aperture, which is consistent with simulations. These results motivated the extension of the baffles surrounding the secondary mirror, with the following reduction in detector optical loading from 2,24 pW to 188pW.
Publication Date: Jul 01, 2012
Document ID:
(Acquired Nov 13, 2012)
Subject Category: ASTRONOMY
Report/Patent Number: GSFC.CP.7100.2012
Document Type: Conference Paper
Meeting Information: Society of Photo-Optical Instrumentation Engineers conference; 1-7 Jul. 2012; Amsterdam; Netherlands
Meeting Sponsor: International Society for Optical Engineering; United States
Financial Sponsor: NASA Goddard Space Flight Center; Greenbelt, MD, United States
NASA Goddard Space Flight Center; Greenbelt, MD, United States
Organization Source: NASA Goddard Space Flight Center; Greenbelt, MD, United States
Description: 11p; In English; Original contains color and black and white illustrations
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: Copyright; Distribution as joint owner in the copyright
Miscellaneous Notes: Sponsored in part by a FONDECYT Iniciacion No. 11100147 and a VRI Inicio 39/2010 award
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