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Proceedings Paper

Quasi-optical verification of the focal plane optics of the heterodyne instrument for the far-infrared (HIFI)
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Paper Abstract

HIFI is one of the three instruments for the Herschel Space Observatory, an ESA cornerstone mission. HIFI is a high resolution spectrometer operating at wavelengths between 157 and 625 μm. The need for a compact layout reducing the volume and mass as much as possible has important consequences for the optical design. Many mirrors are located in the near-field of the propagating beam. Especially in the long wavelength limit diffraction effects might therefore introduce significant amplitude and phase distortions. A classical geometrical optical approach is consequently inadequate. In this paper we present a rigorous quasi-optical analysis of the entire optical system including the signal path, local oscillator path and onboard calibration source optical layout. In order to verify the results of the front-to-end coherent propagation of the detector beams, near-field measurement facilities capable of measuring both amplitude and phase have beam developed. A remarkable feature of these facilities is that the absolute coordinates of the measured field components are known to within fractions of a wavelength. Both measured and simulated fields can therefore compared directly since they are referenced to one single absolute position. We present a comparison of experimental data with software predictions obtained from the following packages: GRASP (Physical Optics Analysis) and GLAD (Plane Wave Decomposition). We also present preliminary results for a method to correct for phase aberrations and optimize the mirror surfaces without changing the predesigned mechanical layout of the optical system.

Paper Details

Date Published: 16 September 2004
PDF: 12 pages
Proc. SPIE 5497, Modeling and Systems Engineering for Astronomy, (16 September 2004); doi: 10.1117/12.551144
Show Author Affiliations
Massimo Candotti, National Univ. of Ireland/Maynooth (Ireland)
Gary A. Cahill, National Univ. of Ireland/Maynooth (Ireland)
Timothy J. Finn, National Univ. of Ireland/Maynooth (Ireland)
Willem Jellema, Space Research Organization Netherlands (Netherlands)
John Lavelle, National Univ. of Ireland/Maynooth (Ireland)
J. Anthony Murphy, National Univ. of Ireland/Maynooth (Ireland)
Creidhe O'Sullivan, National Univ. of Ireland/Maynooth (Ireland)
Neil A. Trappe, National Univ. of Ireland/Maynooth (Ireland)

Published in SPIE Proceedings Vol. 5497:
Modeling and Systems Engineering for Astronomy
Simon C. Craig; Martin J. Cullum, Editor(s)

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