Abstract
The Atacama Cosmology Telescope Polarimeter (ACTPol) is a polarization sensitive receiver for the 6-m Atacama Cosmology Telescope (ACT) and measures the small angular scale polarization anisotropies in the cosmic microwave background (CMB). The full focal plane is composed of three detector arrays, containing over 3000 transition edge sensors (TES detectors) in total. The first two detector arrays, observing at 146 GHz, were deployed in 2013 and 2014, respectively. The third and final array is composed of multichroic pixels sensitive to both 90 and 146 GHz and saw first light in February 2015. Fabricated at NIST, this dichroic array consists of 255 pixels, with a total of 1020 polarization sensitive bolometers and is coupled to the telescope with a monolithic array of broad-band silicon feedhorns. The detectors are read out using time-division SQUID multiplexing and cooled by a dilution refrigerator at 110 mK. We present an overview of the assembly and characterization of this multichroic array in the lab, and the initial detector performance in Chile. The detector array has a TES detector electrical yield of 85 %, a total array sensitivity of less than 10 \(\upmu \)K\(\sqrt{\text {s}}\), and detector time constants and saturation powers suitable for ACT CMB observations.
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Notes
The analysis to estimate time constants from planet scans includes deconvolution of the 200 Hz digital anti-aliasing filter used for the science data-taking mode.
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Acknowledgments
This work was supported by the U.S. National Science Foundation through awards AST-0965625 and PHY-1214379. The NIST authors would like to acknowledge the support of the NIST Quantum Initiative. The development of multichroic detectors and lenses was supported by NASA Grants s NNX13AE56G and NNX14AB58G. The work of KPC, KTC, EG, BJK, CM, BLS, JTW, and SMS was supported by NASA Space Technology Research Fellowship awards.
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Ho, S.P., Pappas, C.G., Austermann, J. et al. The First Multichroic Polarimeter Array on the Atacama Cosmology Telescope: Characterization and Performance. J Low Temp Phys 184, 559–567 (2016). https://doi.org/10.1007/s10909-016-1573-1
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DOI: https://doi.org/10.1007/s10909-016-1573-1