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