POLarization Orientation CALibrator for Cosmology

A Novel Method to Measure the Absolute Polarization Orientation
of the Cosmic Microwave Background

Publications

Nati F. et al., POLOCALC: A Novel Method to Measure the Absolute Polarization Orientation of the Cosmic Microwave Background,
Journal of Astronomical Instrumentation, Volume 6 No.2, 2017, DOI: 10.1142/S2251171717400086

Nati F. et al., Airborne, Far-Field Calibrators for Cosmic Microwave Background Telescopes: POLOCALC, 2018 IEEE Conference on Antenna Measurements & Applications (CAMA), DOI: 10.1109/CAMA.2018.8530526

Coppi G. et al., PROTOCALC: an artificial calibrator source for CMB telescopes, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy XI, Issue 1219015, 2022, SPIE, DOI: 10.1117/12.2628312

POLOCALC Concept: In the sliding cartoons above, ground telescopes measure linearly polarized light coming from the sky. The absolute orientation of the detectors with respect to celestial coordinates is affected by a miscalibration. Therefore, the measured polarization angle (in red) differs from the true angle (in orange). An artificial polarized source (in red) is registered to sky coordinates thanks to a star camera (in orange). The telescopes’ detector orientation is calibrated observing the source signal operating from a balloon, an aerial drones or a ground platfrom.

E to B modes leakage: In the interactive example below, the pattern on the left represent a polarization pattern. The initial pure E-mode signal can be gradually converted into B-mode by an isotropic rotation of the polarization orientation. At 45° all the E-mode pattern is converted into B-mode. Play with the horizontal cursor and change the miscalibration angle: it will convert E into B modes and vice versa. Such a coherent rotation is equivalent to a detector angle miscalibration. POLOCALC will calibrate the absolute polarization angle and avoid E to B leakage.