Abstract: The Cosmology Large Angular Scale Surveyor (CLASS) aims to characterize the primordial gravitational waves at the level of tensor-to-scalar ratio of 0.01 and make a near cosmic-variance-limited measurement of the optical depth to reionization. CLASS is an array of four telescopes that surveys 70% of the microwave sky from the Atacama Desert at 40, 90, 150, and 220 GHz frequency bands. A unique combination of large sky coverage, rapid front-end polarization modulator, broad frequency coverage, and background-limited detectors enables CLASS to characterize the B-mode and E-mode power spectra on both the reionization and recombination scales. The detector arrays for all four CLASS telescopes contain smooth-walled feedhorns that couple to transition-edge sensor bolometers through planar orthomode transducers fabricated on monocrystalline silicon.

In this talk, I will give an overview of the design and performance of the CLASS detectors and provide an update on early results and project status.