Speaker
Description
The BICEP3 telescope is a 95GHz CMB polarimeter located at the South Pole searching for inflationary gravitational waves. Directly measuring non-idealities in polarization between detector pairs and across the focal plane is useful for understanding how our constraints on r are impacted by E-to-B leakage. Further, measuring polarization angles in an absolute reference frame makes telescopes sensitive to potential signatures from EM parity violation such as cosmic birefringence. We calibrate our detectors on BICEP3 by observing a rotating polarized source (RPS) whose polarization is carefully referenced to gravity. Current birefringence constraints are limited to ~0.1° by calibration precision and statistical uncertainty, but as more CMB data are gathered, calibration uncertainty becomes dominant. This talk will discuss the challenges in building a highly precise (~0.03°) polarization calibrator and ensuring true absolute calibration.
