Characterization and performance of the second-year SPT-3G focal plane

TL;DR

This paper details the characterization and performance improvements of the second-year SPT-3G focal plane, which includes new detector arrays with enhanced mapping speed and overall performance for the South Pole Telescope's third-generation instrument.

Contribution

The paper presents the replacement and tuning of all ten detector wafers in the SPT-3G focal plane, improving its mapping speed and performance metrics compared to the first year.

Findings

Optimized TES transition temperature and resistance.

Enhanced detector saturation power and bandpass properties.

High array yield and optical efficiency achieved.

Abstract

The third-generation instrument for the 10-meter South Pole Telescope, SPT-3G, was first installed in January 2017. In addition to completely new cryostats, secondary telescope optics, and readout electronics, the number of detectors in the focal plane has increased by an order of magnitude from previous instruments to ~16,000. The SPT-3G focal plane consists of ten detector modules, each with an array of 269 trichroic, polarization-sensitive pixels on a six-inch silicon wafer. Within each pixel is a broadband, dual-polarization sinuous antenna; the signal from each orthogonal linear polarization is divided into three frequency bands centered at 95, 150, and 220 GHz by in-line lumped element filters and transmitted via superconducting microstrip to Ti/Au transition-edge sensor (TES) bolometers. Properties of the TES film, microstrip filters, and bolometer island must be tightly controlled to achieve optimal performance. For the second year of SPT-3G operation, we have replaced all ten wafers in the focal plane with new detector arrays tuned to increase mapping speed and improve overall performance. Here we discuss the TES superconducting transition temperature and normal resistance, detector saturation power, bandpasses, optical efficiency, and full array yield for the 2018 focal plane.