Metamaterial Optics for Precision Cosmic Microwave Background Observation

The Cosmic Microwave Background (CMB) is the oldest light in the Universe. As such it provides deep insight into both early and late Universe physics, including the sum of the neutrino masses and possible signatures of inflation. To better characterize the temperature and polarization anisotropies of the CMB, new instruments need to be designed. The Atacama Cosmology Telescope (ACT) is a six meter telescope built to observe the CMB. This thesis describes contributions to new broadband receivers called ACTPol and Advanced ACTPol. The receiver has three independent cameras with feedhorn coupled, polarization sensitive superconducting bolometer detectors. The first two detector arrays for ACTPol are sensitive to 150 GHz. The other detector arrays are dichroic, sensitive to two frequency bands: the low frequency (20/40 GHz), mid frequency (90/150 GHz), and high frequency (150/220 GHz). I have further developed the three layer metamaterial antireflection (AR) coating technology used to realize the necessary bandwidth for the current dichroic detectors for the ACTPol and Advanced ACTPol instruments. In this thesis I describe work to push the boundaries of that technology beyond the current needs, and develop broader bandwidth, five layer AR coatings which could effectively cover 50-350 GHz, and higher frequency coatings which could work up to 2 THz. I also applied the metamaterial design and fabrication techniques to a different optical element for CMB observation: half-wave plates (HWPs). I began with a simple single frequency HWP for the ACTPol instrument, then went to a broadband, three stack HWP for the ACTPol and Advanced ACTPol dichroic bands. These HWPs represent a novel use of metamaterial technology, with significant benefits over traditional found material HWPs. With these optical elements, the ACT collaboration has published a number of scientific papers. We have reported new measurements of the temperature and polarization power spectra of the CMB. We have used the Sunayev-Zeldovich effect to measure the masses of galaxy clusters. We have detected the effects of gravitational lensing on the CMB, and compared this lensing mass profile to optical lensing measurements. This thesis is organized as follows. Chapter 1 gives an overview of Cosmology, including its history and current goals. Chapter 2 is a detailed description of the Atacama Cosmology Telescope and its various instrumentation. In Chapter 3 I discuss my work on the antireflection coatings. Chapter 4 is about my work on half-wave plates. Chapter 5 concludes with a discussion of the science my work has enabled and the future of the work presented in this thesis and CMB observations in general.PHDPhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/146072/1/kpcoughl_1.pd