BICEP3: a 95GHz refracting telescope for degree-scale CMB polarization

Bicep3 is a 550 mm-aperture refracting telescope for polarimetry of radiation in the cosmic microwave back-ground at 95 GHz. It adopts the methodology of Bicep1, Bicep2 and the Keck Array experiments — it pos-sesses sufficient resolution to search for signatures of the inflation-induced cosmic gravitational-wave background while utilizing a compact design for ease of construction and to facilitate the characterization and mitigation of systematics. However, Bicep3 represents a significant breakthrough in per-receiver sensitivity, with a focal plane area 5 × larger than a Bicep2/Keck Array receiver and faster optics (f/1.6 vs. f/2.4). Large-aperture infrared-reflective metal-mesh filters and infrared-absorptive cold alumina filters and lenses were developed and implemented for its optics. The camera consists of 1280 dual-polarization pixels; each is a pair of orthogonal antenna arrays coupled to transition-edge sensor bolometers and read out by multiplexed SQUIDs. Upon de-ployment at the South Pole during the 2014-15 season, Bicep3 will have survey speed comparable to Keck Arra