Feedhorn-coupled TES polarimeter camera modules at 150 GHz for CMB polarization measurements with SPTpol

TL;DR

This paper describes the design, characterization, and properties of 150 GHz feedhorn-coupled TES polarimeter modules for CMB polarization measurements with the SPTpol camera, emphasizing their fabrication, performance, and readiness for deployment.

Contribution

It introduces a new design and characterization of 150 GHz TES polarimeter modules with high optical efficiency and fast response, suitable for CMB polarization studies.

Findings

Detectors have an average critical temperature of 478 mK.

Modules exhibit an optical efficiency of approximately 90%.

Electrothermal time constants are less than 1 ms.

Abstract

The SPTpol camera is a dichroic polarimetric receiver at 90 and 150 GHz. Deployed in January 2012 on the South Pole Telescope (SPT), SPTpol is looking for faint polarization signals in the Cosmic Microwave Background (CMB). The camera consists of 180 individual Transition Edge Sensor (TES) polarimeters at 90 GHz and seven 84-polarimeter camera modules (a total of 588 polarimeters) at 150 GHz. We present the design, dark characterization, and in-lab optical properties of the 150 GHz camera modules. The modules consist of photolithographed arrays of TES polarimeters coupled to silicon platelet arrays of corrugated feedhorns, both of which are fabricated at NIST-Boulder. In addition to mounting hardware and RF shielding, each module also contains a set of passive readout electronics for digital frequency-domain multiplexing. A single module, therefore, is fully functional as a miniature focal plane and can be tested independently. Across the modules tested before deployment, the detectors average a critical temperature of 478 mK, normal resistance R_N of 1.2 Ohm, unloaded saturation power of 22.5 pW, (detector-only) optical efficiency of ~ 90%, and have electrothermal time constants < 1 ms in transition.