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Published August 19, 2014 | Published
Book Section - Chapter Open

Keck array and BICEP3: spectral characterization of 5000+ detectors


The inflationary paradigm of the early universe predicts a stochastic background of gravitational waves which would generate a B-mode polarization pattern in the cosmic microwave background (CMB) at degree angular scales. Precise measurement of B-modes is one of the most compelling observational goals in modern cosmology. Since 2011, the Keck Array has deployed over 2500 transition edge sensor (TES) bolometer detectors at 100 and 150 GHz to the South Pole in pursuit of degree-scale B-modes, and Bicep3 will follow in 2015 with 2500 more at 100 GHz. Characterizing the spectral response of these detectors is important for controlling systematic effects that could lead to leakage from the temperature to polarization signal, and for understanding potential coupling to atmospheric and astrophysical emission lines. We present complete spectral characterization of the Keck Array detectors, made with a Martin-Puplett Fourier Transform Spectrometer at the South Pole, and preliminary spectra of Bicep3 detectors taken in lab. We show band centers and effective bandwidths for both Keck Array bands, and use models of the atmosphere at the South Pole to cross check our absolute calibration. Our procedure for obtaining interferograms in the field with automated 4-axis coupling to the focal plane represents an important step towards efficient and complete spectral characterization of next-generation instruments more than 10000 detectors.

Additional Information

© 2014 Society of Photo-Optical Instrumentation Engineers (SPIE). The Keck Array and Bicep3 projects have been made possible through support from the National Science Foundation (grant Nos. 0742818, 0742592, 1044978, 1110087, 1145172, 1313158, 1313010, 1313062, 1313287, 1056465, and 0960243), the W. M. Keck Foundation, the Canada Foundation for Innovation, and the British Columbia Development Fund. The development of antenna-coupled detector technology was supported by the JPL Research and Technology Development Fund and grants 06-ARPA206-0040 and 10-SAT10-0017 from the NASA ARPA and SAT programs. The development and testing of focal planes were supported by the Gordon and Betty Moore Foundation at Caltech. The computations in these proceedings were run on the Odyssey cluster supported by the FAS Science Division Research Computing Group at Harvard University. Tireless administrative support was provided by Irene Coyle, Kathy Deniston, Donna Hernandez, and Dana Volponi. We are grateful to Robert Schwarz as our 2011–2014 Keck Array winterover. We thank the staff of the US Antarctic Program and in particular the South Pole Station without whose help this research would not have been possible. We thank our Bicep1, Bicep2, and Spider colleagues for useful discussions and shared expertise.

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