Multi-chroic dual-polarization bolometric detectors for studies of the Cosmic Microwave Background

TL;DR

This paper presents the development and testing of multi-chroic dual-polarization bolometric detectors designed for enhanced CMB polarization measurements, offering increased mapping speed and foreground discrimination without added weight or cryogenic complexity.

Contribution

The paper introduces a novel multi-chroic antenna-coupled TES detector design with broadband filters and high-performance optical characteristics for CMB studies.

Findings

Detectors achieve low ellipticity and cross-polarization leakage.

Optical data demonstrate effective band partitioning with multiple filters.

Broadband anti-reflection coatings show near 100% bandwidth with no cryogenic loss.

Abstract

We are developing multi-chroic antenna-coupled TES detectors for CMB polarimetry. Multi-chroic detectors increase the mapping speed per focal plane area and provide greater discrimination of polarized galactic foregrounds with no increase in weight or cryogenic cost. In each pixel, a silicon lens-coupled dual polarized sinuous antenna collects light over a two-octave frequency band. The antenna couples the broadband millimeter wave signal into microstrip transmission lines, and on-chip filter banks split the broadband signal into several frequency bands. Separate TES bolometers detect the power in each frequency band and linear polarization. We will describe the design and performance of these devices and present optical data taken with prototype pixels. Our measurements show beams with percent level ellipticity, percent level cross-polarization leakage, and partitioned bands using banks of 2, 3, and 7 filters. We will also describe the development of broadband anti-reflection coatings for the high dielectric constant lens. The broadband anti-reflection coating has approximately 100 percent bandwidth and no detectable loss at cryogenic temperature. Finally, we will describe an upgrade for the POLARBEAR CMB experiment and installation for the LITEBird CMB satellite experiment both of which have focal planes with kilo-pixel of these detectors to achieve unprecedented mapping speed.