Focal Plane Development for Observations of the Cosmic Microwave Background with the Simons Observatory

Abstract

A promising avenue for studying the origin and evolution of the universe is to measure the Cosmic Microwave Background (CMB), the thermal radiation remaining from the Big Bang after billions of years of expansion. Today, this remnant takes the form of an extraordinarily uniform thermal blackbody of ∼2.7 K in temperature. Increasingly precise measurements of small fluctuations in CMB temperature and polarization have been instrumental in shaping modern understanding of the evolution of the early universe. The Simons Observatory (SO) is a new CMB experiment that will consist of several high-sensitivity polarization sensitive telescopes at ∼5200 m altitude in the Atacama Desert, Chile, observing in frequency bands between 27 GHz and 280 GHz. SO is designed to measure the temperature and polarization of the CMB to constrain cosmological parameters and detect evidence of primordial gravitational waves in the CMB polarization map. To accomplish these ambitious goals, the Simons Observatory must be built to provide unprecedented sensitivity, which requires cutting-edge, high-yield detector and readout technologies. The telescope focal planes are close-packed with Universal Focal Plane Modules (UFMs) at the 100 mK stage. UFMs are mechanically interchangeable assemblies containing stacks of 150-mm silicon wafers with detectors, optical coupling components, and readout components for microwave multiplexing (μMUX). SO will deploy a total of 49 UFMs with over 60,000 bolometers to achieve a multiplexing factor of approximately 1,000. This thesis presents my contributions to the early prototype UFM development, including the completion of sensitivity calculations used to inform design choices, the carrying out of assembly steps to maximize detector readout performance, the cryogenic testing of prototype components, and the development of a novel mathematical algorithm and device for simultaneous short checking for UFM electrical validation.