Performance and on-sky optical characterization of the SPTpol instrument

TL;DR

The paper reports on the design, deployment, and on-sky optical characterization of the SPTpol instrument, a polarization-sensitive camera on the South Pole Telescope, used to measure CMB polarization and test detector technologies.

Contribution

It provides the first on-sky tests of dual TES bolometers and DfMUX readout technology in the SPTpol instrument, advancing CMB polarization measurement capabilities.

Findings

Successful on-sky optical characterization of SPTpol detectors

Validation of dual TES bolometers and DfMUX technology in a real observing environment

Performance metrics indicating readiness for scientific observations

Abstract

In January 2012, the 10m South Pole Telescope (SPT) was equipped with a polarization-sensitive camera, SPTpol, in order to measure the polarization anisotropy of the cosmic microwave background (CMB). Measurements of the polarization of the CMB at small angular scales (~several arcminutes) can detect the gravitational lensing of the CMB by large scale structure and constrain the sum of the neutrino masses. At large angular scales (~few degrees) CMB measurements can constrain the energy scale of Inflation. SPTpol is a two-color mm-wave camera that consists of 180 polarimeters at 90 GHz and 588 polarimeters at 150 GHz, with each polarimeter consisting of a dual transition edge sensor (TES) bolometers. The full complement of 150 GHz detectors consists of 7 arrays of 84 ortho-mode transducers (OMTs) that are stripline coupled to two TES detectors per OMT, developed by the TRUCE collaboration and fabricated at NIST. Each 90 GHz pixel consists of two antenna-coupled absorbers coupled to two TES detectors, developed with Argonne National Labs. The 1536 total detectors are read out with digital frequency-domain multiplexing (DfMUX). The SPTpol deployment represents the first on-sky tests of both of these detector technologies, and is one of the first deployed instruments using DfMUX readout technology. We present the details of the design, commissioning, deployment, on-sky optical characterization and detector performance of the complete SPTpol focal plane.