The Cosmology Large Angular Scale Surveyor ( CLASS ) aims to detect and characterize the primordial B-mode signal and make a sample-variance-limited measurement of the optical depth to reionization .
CLASS is a ground-based , multi-frequency microwave polarimeter that surveys 70 % of the microwave sky every day from the Atacama Desert .
The focal plane detector arrays of all CLASS telescopes contain smooth-walled feedhorns that couple to transition-edge sensor ( TES ) bolometers through symmetric planar orthomode transducer ( OMT ) antennas .
These low noise polarization-sensitive detector arrays are fabricated on mono-crystalline silicon wafers to maintain TES uniformity and optimize optical efficiency throughout the wafer .
In this paper , we discuss the design and characterization of the first CLASS 93 GHz detector array .
We measure the dark parameters , bandpass , and noise spectra of the detectors and report that the detectors are photon-noise limited .
With current array yield of 82 % , we estimate the total array noise-equivalent power ( NEP ) to be 2.1 aW \sqrt [ ] { \mathrm { s } } .