SPTpol: an instrument for CMB polarization

SPTpol will consist of an 850 element polarization sensitive bolometric camera deployed to the South Pole Telescope in late 2011. This camera is optimized for measurement of the polarization of the cosmic microwave background with arcminute resolution. These measurements will be used to constrain neutrino masses and to constrain the amplitude of gravitational waves from inflation. The camera includes two detector architectures that observe in two different frequency bands. At 150 GHz, SPTpol will use 650 feedhorn‐coupled TES polarimeters fabricated at NIST. At 90 GHz, it will use 200 absorber‐coupled polarimeters developed at Argonne National Lab. The NIST pixels will be coupled to the telescope using a monolithic array of corrugated feeds and the Argonne devices will be coupled with individually machined contoured feeds. The entire focal plane will be readout using a digital frequency‐domain multiplexer system. We provide an overview of the project, describe the detectors and discuss the design of this system.