23 July 2014 Polarization properties of a multi-moded feed horn for the Primordial Inflation Explorer mission
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The Primordial Inflation Explorer (PIXIE) is an Explorer-class mission to characterize the cosmic microwave background (CMB). PIXIE will map linear polarization on degree angular scales and larger to search for the gravity-wave signature of primordial inflation, and measure distortions from the blackbody spectrum to constrain energy-releasing processes in the early universe. PIXIE uses multi-moded optics to achieve sensitivity comparable to a kilo-pixel focal plane of diffraction-limited detectors, but using only 4 semiconductor bolometers illuminated by a non-imaging feed horn. PIXIE's frequency coverage extends from 30 GHz to 6 THz. Although the co- and cross-polar response of the feed horn and coupling optics is easily evaluated in the short-wavelength (geometric optics) limit, the response at longer wavelengths is more difficult to model analytically. We have built a coupled feed horn/reflector optical system based on the PIXIE design and measured the co- and cross-polar response at several wavelengths spanning the transition from the few-mode limit at long wavelengths to the geometric optics limit at short wavelengths. We compare the measured co- and cross-polar beam patterns to model predictions and discuss the implications for the PIXIE mission and similar missions using multi-moded optics.
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Alan Kogut, Alan Kogut, Dale J. Fixsen, Dale J. Fixsen, Robert S. Hill, Robert S. Hill, Paul Mirel, Paul Mirel, "Polarization properties of a multi-moded feed horn for the Primordial Inflation Explorer mission", Proc. SPIE 9153, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy VII, 915318 (23 July 2014); doi: 10.1117/12.2056873; https://doi.org/10.1117/12.2056873

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