Antenna-coupled TES bolometers used in BICEP2, Keck array, and SPIDER

TL;DR

This paper presents the design, performance, and deployment of antenna-coupled TES bolometers for CMB polarization experiments, demonstrating high sensitivity, spectral control, and scalability in multiple instruments.

Contribution

It introduces a scalable antenna-coupled TES bolometer design with high optical efficiency and low cross-polarization, successfully deployed in BICEP2, Keck Array, and SPIDER.

Findings

Achieved 20-30% bandwidth spectral bands at 95, 150, 220 GHz.

Deployed 2560 detectors with a combined sensitivity of ~9 uK-rt in Keck Array.

Demonstrated high optical efficiency (~35%) and low cross-polarization (~0.5%).

Abstract

We have developed antenna-coupled transition-edge sensor (TES) bolometers for a wide range of cosmic microwave background (CMB) polarimetry experiments, including BICEP2, Keck Array, and the balloon borne SPIDER. These detectors have reached maturity and this paper reports on their design principles, overall performance, and key challenges associated with design and production. Our detector arrays repeatedly produce spectral bands with 20%-30% bandwidth at 95, 150, or 220~GHz. The integrated antenna arrays synthesize symmetric co-aligned beams with controlled side-lobe levels. Cross-polarized response on boresight is typically ~0.5%, consistent with cross-talk in our multiplexed readout system. End-to-end optical efficiencies in our cameras are routinely 35% or higher, with per detector sensitivities of NET~300 uKrts. Thanks to the scalability of this design, we have deployed 2560 detectors as 1280 matched pairs in Keck Array with a combined instantaneous sensitivity of ~9 uKrts, as measured directly from CMB maps in the 2013 season. Similar arrays have recently flown in the SPIDER instrument, and development of this technology is ongoing.