The CLASS 150/220 GHz Polarimeter Array: Design, Assembly, and
  Characterization
  We report on the development of a polarization-sensitive dichroic (150/220
GHz) detector array for the Cosmology Large Angular Scale Surveyor (CLASS)
delivered to the telescope site in June 2019. In concert with existing 40 and
90 GHz telescopes, the 150/220 GHz telescope will make observations of the
cosmic microwave background over large angular scales aimed at measuring the
primordial B-mode signal, the optical depth to reionization, and other
fundamental physics and cosmology. The 150/220 GHz focal plane array consists
of three detector modules with 1020 transition edge sensor (TES) bolometers in
total. Each dual-polarization pixel on the focal plane contains four bolometers
to measure the two linear polarization states at 150 and 220 GHz. Light is
coupled through a planar orthomode transducer (OMT) fed by a smooth-walled
feedhorn array made from an aluminum-silicon alloy (CE7). In this work, we
discuss the design, assembly, and in-lab characterization of the 150/220 GHz
detector array. The detectors are photon-noise limited, and we estimate the
total array noise-equivalent power (NEP) to be 2.5 and 4 aW$\sqrt{\mathrm{s}}$
for 150 and 220 GHz arrays, respectively.
