Calibration System with Cryogenically-Cooled Loads for CMB Polarization Detectors

TL;DR

This paper introduces a cryogenically-cooled load calibration system for CMB polarization detectors, enabling laboratory generation of polarized signals comparable to ground-based observations, improving pre-deployment characterization.

Contribution

It presents a novel calibration system using cryogenically-cooled blackbody absorbers, extending traditional methods for more accurate CMB polarimeter testing.

Findings

Successfully demonstrated calibration with a coherent polarimeter

Generated polarized signals similar to ground-based observations

Applicable to both coherent and incoherent polarimeters

Abstract

We present a novel system to calibrate millimeter-wave polarimeters for CMB polarization measurements. This technique is an extension of the conventional metal mirror rotation approach, however it employs cryogenically-cooled blackbody absorbers. The primary advantage of this system is that it can generate a slightly polarized signal ($\sim100$ mK) in the laboratory; this is at a similar level to that measured by ground-based CMB polarization experiments observing a $\sim$ 10 K sky. It is important to reproduce the observing condition in the laboratry for reliable characterization of polarimeters before deployment. In this paper, we present the design and principle of the system, and demonstrate its use with a coherent-type polarimeter used for an actual CMB polarization experiment. This technique can also be applied to incoherent-type polarimeters and it is very promising for the next-generation CMB polarization experiments.