Development of Multi-chroic Millimeter-wave Polarization Sensitive Detector Arrays

During my NSTRF, I developed a system for machining precision subwavelength meta material features to form an anti-reflection surface treatment on silicon optics for millimeter-wavelength telescopes. I then fabricated several of these optics, and deployed them on the Atacama Cosmology Telescope Polarization (ACTPol) project. Following this, I developed silicon-substrate free-space filters that leveraged the existing anti-reflection metamaterial capability. I also worked on developing real-space Cosmic Microwave Background (CMB) modeling to improve our understanding of the impacts of gravitational lensing and the Sunyaev-Zel’dovich effect on the observed CMB sky. Over the course of my fellowship, I developed several technologies that substantively improved the state-of-the-art in millimeter and submillimeter wavelength telescope optics, and then did simulation work in support of improving current and next-generation cosmic microwave background lensing measurements. The technology development portion consisted of two main projects, the development of metamaterial anti reflection silicon optics and the development of free-space filters on metamaterial silicon substrates. I developed the fabrication capability to precisely machine sub-wavelength features (<5um tolerances on ~100um features) into the surfaces of large diameter (35+ cm) silicon lenses, in order to efficiently couple light into and out of the optics (with the sub-wavelength features acting as metamaterial layers that performed as an anti-reflection coating). This technology improved the overall optical throughput of an ACTPol optics tube significantly (reducing the total light lost to reflections and absorption from ~15% to <1%), and enabled the deployment of the first array of multi-frequency pixels on a CMB telescope. This allowed for the successful conclusion of the ACTPol project and enabled the next-generation Advanced ACTPol project (which consists entirely of multi-frequency arrays and additional metamaterial silicon optics fabricated with the system I designed). Following this, I designed and fabricated infrared-blocking free-space filters taking advantage of the antireflection metamaterial silicon as a better substrate than existing plastic-substrate filters. These filters allow for composite structures formed with reflective, absorptive, and scattering behavior that can be tuned to block a wide range of frequencies, and block infrared radiation more efficiently than the plastic-substrate and bulk-material filters that are currently in use on CMB telescopes while maintaining high transmission in the instrument bands. I also developed a simulation framework that generates a realistically lensed CMB sky by taking an object catalog from n-body simulations, calculating the real-space lensing deflections introduced by each object, and applying them as a distortion to the base CMB. This, in combination with an existing simulation pipeline that handles the Sunyaev-Zel’dovich effect, allows for complete generation of realistic CMB skies while accurately accounting for the influences of galaxy clusters (including spatially correlated effects that can’t be realistically accounted for using only the power spectrum behavior of the CMB).