On-sky performance of new 90 GHz detectors for the Cosmology Large Angular Scale Surveyor (CLASS)

TL;DR

This paper reports on the on-sky performance of upgraded 90 GHz detectors in the CLASS telescope, highlighting design improvements and their impact on optical efficiency during observations of Jupiter.

Contribution

It introduces new detector modules with improved design for the 90 GHz telescope and evaluates their on-sky optical efficiency through observational data.

Findings

Enhanced optical efficiency observed after upgrade

Successful implementation of new detector modules

Improved detector stability during observations

Abstract

The Cosmology Large Angular Scale Surveyor (CLASS) is a polarization-sensitive telescope array located at an altitude of 5,200 m in the Chilean Atacama Desert and designed to measure the polarized Cosmic Microwave Background (CMB) over large angular scales. The CLASS array is currently observing with three telescopes covering four frequency bands: one at 40 GHz (Q); one at 90 GHz (W1); and one dichroic system at 150/220 GHz (HF). During the austral winter of 2022, we upgraded the first 90 GHz telescope (W1) by replacing four of the seven focal plane modules. These new modules contain detector wafers with an updated design, aimed at improving the optical efficiency and detector stability. We present a description of the design changes and measurements of on-sky optical efficiencies derived from observations of Jupiter.