For more than 50 years, measurements of the cosmic microwave background (CMB)
have provided insight into the nature of the universe we inhabit. We've
measured the CMB's temperature anisotropy to high precision through a
combination of ground- and space-based experiments; now we turn our attention
to measuring the CMB's polarization anisotropy. If these measurements are good
enough we may see the first direct evidence for gravitational waves predicted
by inflation. But it turns out this is difficult to do! In order to tease apart
the gravitational wave signal from other confounding signals we need to observe
the CMB on both ~degree and ~arcminute scales, and we need to do so with
exceptionally sensitive instruments. In this thesis defense I will discuss my
work developing millimeter-wave antireflection coatings for one such
instrument: the South Pole Telescope's third generation survey camera (SPT-3G).
SPT-3G was deployed in 2016/2017 and is designed for high-cadence CMB mapping
with arcminute-scale resolution in three different colors. The camera achieves
a 10x increase in detector count over its predecessor thanks to advances in
detector fabrication capabilities, readout multiplexing technology, and the
optical techniques that are the focus of this talk. SPT-3G uses ceramic lenses
to focus the CMB radiation onto its detectors, but the bare ceramic is highly
reflective---so we apply a coating to increase the fraction of light that lands
on our detectors. We've developed two processes and two coatings for the SPT-3G
optics: one for the three 720 mm diameter reimaging lenses and single infrared
filter, and one for the 2,710 5 mm diameter dielectric lenses at the focal
plane. I will discuss both of these coatings---the techniques we use to
manufacture them, and laboratory measurements of their performance---and how
they may be useful for the upcoming CMB-S4 mission.
