Candotti, Massimo and Cahill, G. and Finn, Timothy J. and Jellema, Willem and Lavelle, John and Murphy, J.Anthony and O'Sullivan, Créidhe and Trappe, Neil (2004) Quasi-optical verification of the focal plane optics of the heterodyne instrument for the far-infrared (HIFI). Proceedings of SPIE, 5497. ISSN 0277-786X

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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.

Item Type:	Article
Additional Information:	The authors would like to acknowledge the support of Enterprise Ireland (Prodex).
Keywords:	experimental verification; far-infrared; near-field; beam propagation; electromagnetic simulations;
Academic Unit:	Faculty of Science and Engineering > Experimental Physics
Item ID:	14007
Identification Number:	https://doi.org/10.1117/12.551144
Depositing User:	Dr. Anthony Murphy
Date Deposited:	12 Feb 2021 15:54
Journal or Publication Title:	Proceedings of SPIE
Publisher:	SPIE
Refereed:	Yes
Funders:	Enterprise Ireland
URI:	Publisher
Use Licence:	This item is available under a Creative Commons Attribution Non Commercial Share Alike Licence (CC BY-NC-SA). Details of this licence are available here

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