POLARBEAR-2A is the first receiver for the Simons Array cosmic micmwave background polarization experiment. POLARBEAR-2A has transition-edge sensor bolometers on the focal plane. Signals from bolometers arc multiplexed and read out by a single SQUID. The receiver was deployed in late 2018 in Atacama, Chile, and operation started in 2019, where rapid confirmation of correspondence between bolometers and multiplexed readout channels was important as an initial step of performance validation. For this purpose, we devised a method using a coherent source that allows us to identify the frequency band and polarization sensitivity angle for each readout channel without detailed bolometer tuning.
