12:00–1:00 pm ERC 401
Grace Chesmore "Characterizing the Simons Observatory Large Aperture Telescope Receiver with Radio Holography"
The Simons Observatory (SO) will observe the cosmic microwave background (CMB) temperature and polarization signals using a series of millimeter-wave telescopes. SO will provide new constraints on inflationary signals and neutrino mass, while further improving our understanding of dark matter, dark energy and galaxy evolution and the era of cosmic reionization. Realizing the SO science goals depends on achieving stringent sensitivity requirements and controlling systematic effects to be subdominant to the statistical noise. To achieve this, the optics tubes must form a clean beam with well controlled side-lobe power. I will present a new approach to laboratory testing, using the technique of near-field radio holography, to measure the complex beam as it emerges from the telescope. Then, using Fresnel diffraction (FD), I propagate these measured fields through the optical system to determine the spill past the mirrors of the telescope and the far-field beam pattern expected of the telescope fed by this receiver. These measurements informed the removal of a filter, which lead to a reduction in side-lobe power. With this change, the spill is less than 1% and the main beam and its side-lobes are consistent with predictions. This approach is broadly applicable to millimeter and sub-millimeter instruments.
Austin Joyce "What defines a theory of gravity?"
I will describe some general aspects of gravitational physics and how these features are related to symmetries of the gravitational sector.
