16 September 2004 Quasi-optical verification of the focal plane optics of the heterodyne instrument for the far-infrared (HIFI)
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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.
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Massimo Candotti, Massimo Candotti, Gary A. Cahill, Gary A. Cahill, Timothy J. Finn, Timothy J. Finn, Willem Jellema, Willem Jellema, John Lavelle, John Lavelle, J. Anthony Murphy, J. Anthony Murphy, Creidhe O'Sullivan, Creidhe O'Sullivan, Neil A. Trappe, Neil A. Trappe, "Quasi-optical verification of the focal plane optics of the heterodyne instrument for the far-infrared (HIFI)", Proc. SPIE 5497, Modeling and Systems Engineering for Astronomy, (16 September 2004); doi: 10.1117/12.551144; https://doi.org/10.1117/12.551144
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