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Proceedings Paper

Modeling multimode feed-horn coupled bolometers for millimeter-wave and terahertz astronomical instrumentation
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Paper Abstract

Multimode horn antennas can be utilized as high efficiency feeds for bolometric detectors, providing increased throughput and sensitivity over single mode feeds, while also ensuring good control of beam pattern characteristics. Multimode horns were employed in the highest frequency channels of the European Space Agency Planck Telescope, and have been proposed for future terahertz instrumentation, such as SAFARI for SPICA. The radiation pattern of a multimode horn is affected by the details of the coupling of the higher order waveguide modes to the bolometer making the modeling more complicated than in the case of a single mode system. A typical cavity coupled bolometer system can be most efficiently simulated using mode matching, typically with smooth walled waveguide modes as the basis and computing an overall scattering matrix for the horn-waveguide-cavity system that includes the power absorption by the absorber. In this paper we present how to include a cavity coupled bolometer, modelled as a thin absorbing film with particular interest in investigating the cavity configuration for optimizing power absorption. As an example, the possible improvements from offsetting the axis of a cylindrically symmetric absorbing cavity from that of a circular waveguide feeding it (thus trapping more power in the cavity) are discussed. Another issue is the effect on the optical efficiency of the detectors of the presence of any gaps, through which power can escape. To model these effects required that existing in-house mode matching software, which calculates the scattering matrices for axially symmetric waveguide structures, be extended to be able to handle offset junctions and free space gaps. As part of this process the complete software code 'PySCATTER' was developed in Python. The approach can be applied to proposed terahertz systems, such as SPICASAFARI.

Paper Details

Date Published: 19 July 2016
PDF: 10 pages
Proc. SPIE 9914, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy VIII, 99142R (19 July 2016); doi: 10.1117/12.2231444
Show Author Affiliations
Eimante Kalinauskaite, National Univ. of Ireland, Maynooth (Ireland)
Anthony Murphy, National Univ. of Ireland, Maynooth (Ireland)
Ian McAuley, National Univ. of Ireland, Maynooth (Ireland)
Neil A. Trappe, National Univ. of Ireland, Maynooth (Ireland)
Colm P. Bracken, National Univ. of Ireland, Maynooth (Ireland)
Darragh N. McCarthy, National Univ. of Ireland, Maynooth (Ireland)
Stephen Doherty, National Univ. of Ireland, Maynooth (Ireland)
Marcin L. Gradziel, National Univ. of Ireland, Maynooth (Ireland)
Creidhe O'Sullivan, National Univ. of Ireland, Maynooth (Ireland)
Bruno Maffei, The Univ. of Manchester (United Kingdom)
Jean-Michel A. Lamarre, Observatoire de Paris (France)
Peter A. R. Ade, Cardiff Univ. (United Kingdom)
Giorgio Savini, Univ. College London (United Kingdom)


Published in SPIE Proceedings Vol. 9914:
Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy VIII
Wayne S. Holland; Jonas Zmuidzinas, Editor(s)

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