# Open Group seminar:  Rahul Datta (Johns Hopkins University)

3:30–4:30 pm ERC 401

### Rahul Datta (Johns Hopkins University) "Cosmology Large Angular Scale Surveyor (CLASS): Detectors and Optical Characterization of the 90 GHz Telescope"

The Cosmology Large Angular Scale Surveyor (CLASS) telescope array surveys 75% of the sky from the Atacama Desert in Chile, at frequency bands centered near 40, 90, 150, and 220 GHz. CLASS measures the largest-angular-scale CMB polarization with the aim of constraining the tensor-to-scalar ratio, $r$, and the optical depth to the surface of last scattering, $\tau$, to near the cosmic variance limit. The Q-band (40 GHz) and W-band (90 GHz) telescopes have been observing since 2016 and 2018, respectively. The G-band telescope housing a dichroic receiver (150/220 GHz) began observing in 2019. I will present an overview of the instrument and progress of the survey. I will describe the optical characterization of the W-band telescope. I will also discuss the design of the latest CLASS W-band detectors currently being deployed, focusing on modifications to address issues of stability and uniformity of optical efficiency.

Seminars

Jun 29