Planck pre-launch status: The optical architecture of the HFI

¹ Astronomy and Instrumentation Group, Cardiff University, Cardiff, Wales, UK
² Optical Science Laboratory, University College London (UCL), Gower Street, WC1E 6BT London, UK e-mail: gs@star.ucl.ac.uk
³ LERMA, CNRS, Observatoire de Paris, 61 avenue de l'Observatoire, 75014 Paris, France
⁴ Department of Physics, Stanford University, Stanford, CA 94305-4060, USA
⁵ Department of Experimental Physics, National University of Ireland (NUI), Maynooth, Co. Kildare, Ireland
⁶ Laboratoire d'Astrophysique Observatoire de Grenoble (LOAG), CNRS, BP 53, 38041 Grenoble Cedex 9, France
⁷ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
⁸ Department of Physics, Princeton University, Princeton NJ 08544, USA
⁹ Department of Physics, California Institute of Technology, Mail code: 59-33, Pasadena, CA 91125, USA
¹⁰ IAS, Institut d'Astrophysique Spatiale, CNRS Université Paris 11, Bâtiment 121, 91405 Orsay, France
¹¹ The University of Manchester, JBCA, School of Physics and Astronomy, Manchester M13 9PL, UK
¹² CESR, CNRS, 9 Av. du colonel Roche, BP44346, 31038 Toulouse Cedex 4, France
¹³ SUPA, Institute for Astronomy, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
¹⁴ Institute of Radiophysics and Electronics, NAS of Ukraine, 12 Proskura St., 61085, Kharkov, Ukraine

Received: 31 July 2009
Accepted: 21 December 2009

Abstract

The Planck High Frequency Instrument, HFI, has been designed to allow a clear unobscured view of the CMB sky through an off-axis Gregorian telescope. The prime science target is to measure the polarized anisotropy of the CMB with a sensitivity of 1 part in 10⁶ with a maximum spatial resolution of 5 arcmin (C_l ~ 3000) in four spectral bands with two further high-frequency channels measuring total power for foreground removal. These requirements place critical constraints on both the telescope configuration and the receiver coupling and require precise determination of the spectral and spatial characteristics at the pixel level, whilst maintaining control of the polarisation. To meet with the sensitivity requirements, the focal plane needs to be cooled with the optics at a few Kelvin and detectors at 100 mK. To limit inherent instrumental thermal emission and diffraction effects, there is no vacuum window, so the detector feedhorns view the telescope secondary directly. This requires that the instrument is launched warm with the cooler chain only being activated during its cruise to L2. Here we present the novel optical configuration designed to meet with all the above criteria.