Planck pre-launch status: Low Frequency Instrument optics

M. Sandri¹, F. Villa¹, M. Bersanelli², C. Burigana¹, R. C. Butler¹, O. D'Arcangelo³, L. Figini³, A. Gregorio^4,5, C. R. Lawrence⁶, D. Maino², N. Mandolesi¹, M. Maris⁴, R. Nesti⁷, F. Perrotta⁸, P. Platania³, A. Simonetto³, C. Sozzi³, J. Tauber⁹ and L. Valenziano¹

¹ INAF-IASF Bologna, via Gobetti 101, 40129 Bologna, Italy e-mail: [sandri;villa;burigana;butler;mandolesi;valenziano]@iasfbo.inaf.it
² Università degli Studi di Milano, via Celoria 16, 20133 Milano, Italy e-mail: [marco.bersanelli;davide.maino]@mi.infn.it
³ IFP-CNR, via Cozzi 53, Milano, Italy e-mail: [darcangelo;platania;simonetto;sozzi]@ifp.cnr.it
⁴ INAF-OATS, via Tiepolo 11, 34143 Trieste, Italy e-mail: maris@oats.inaf.it
⁵ University of Trieste, Department of Physics, via Valerio 2, 34127 Trieste, Italy e-mail: anna.gregorio@ts.infn.it
⁶ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena CA 91109, USA e-mail: Charles.R.Lawrence@jpl.nasa.gov
⁷ Osservatorio Astrofisico di Arcetri, INAF, Largo E. Fermi 5, 50125 Florence, Italy e-mail: nesti@arcetri.astro.it
⁸ SISSA, via Beirut 4, 34014 Trieste, Italy e-mail: perrotta@sissa.it
⁹ ESA ESTEC, PO Box 299, 2200 AG Noordwijk, The Netherlands e-mail: jtauber@rssd.esa.int

Received: 14 July 2009
Accepted: 1 October 2009

Abstract

We describe the optical design and optimisation of the Low Frequency Instrument (LFI), one of two instruments onboard the Planck satellite, which will survey the cosmic microwave background with unprecedented accuracy. The LFI covers the 30–70 GHz frequency range with an array of cryogenic radiometers. Stringent optical requirements on angular resolution, sidelobes, main beam symmetry, polarization purity, and feed orientation have been achieved. The optimisation process was carried out by assuming an ideal telescope according to the Planck design and by using both physical optics and multi-reflector geometrical theory of diffraction. This extensive study led to the flight design of the feed horns, their characteristics, arrangement, and orientation, while taking into account the opto-mechanical constraints imposed by complex interfaces in the Planck focal surface.