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Proceedings Paper

Optical performance of the JWST/MIRI flight model: characterization of the point spread function at high resolution
Author(s): P. Guillard; T. Rodet; S. Ronayette; J. Amiaux; A. Abergel; V. Moreau; J. L. Augueres; A. Bensalem; T. Orduna; C. Nehmé; A. R. Belu; E. Pantin; P.-O. Lagage; Y. Longval; A. C. H. Glasse; P. Bouchet; C. Cavarroc; D. Dubreuil; S. Kendrew
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Paper Abstract

The Mid Infra Red Instrument (MIRI) is one of the four instruments onboard the James Webb Space Telescope (JWST), providing imaging, coronagraphy and spectroscopy over the 5 - 28 μm band. To verify the optical performance of the instrument, extensive tests were performed at CEA on the flight model (FM) of the Mid-InfraRed IMager (MIRIM) at cryogenic temperatures and in the infrared. This paper reports on the point spread function (PSF) measurements at 5.6 μm, the shortest operating wavelength for imaging. At 5.6 μm, the PSF is not Nyquist-sampled, so we use am original technique that combines a microscanning measurement strategy with a deconvolution algorithm to obtain an over-resolved MIRIM PSF. The microscanning consists in a sub-pixel scan of a point source on the focal plane. A data inversion method is used to reconstruct PSF images that are over-resolved by a factor of 7 compared to the native resolution of MIRI. We show that the FWHM of the high-resolution PSFs were 5 - 10 % wider than that obtained with Zemax simulations. The main cause was identified as an out-of-specification tilt of the M4 mirror. After correction, two additional test campaigns were carried out, and we show that the shape of the PSF is conform to expectations. The FWHM of the PSFs are 0.18 - 0.20 arcsec, in agreement with simulations. 56.1 - 59.2% of the total encircled energy (normalized to a 5 arcsec radius) is contained within the first dark Airy ring, over the whole field of view. At longer wavelengths (7.7 - 25.5 μm), this percentage is 57 - 68 %. MIRIM is thus compliant with the optical quality requirements. This characterization of the MIRIM PSF, as well as the deconvolution method presented here, are of particular importance, not only for the verification of the optical quality and the MIRI calibration, but also for scientific applications.

Paper Details

Date Published: 5 August 2010
PDF: 13 pages
Proc. SPIE 7731, Space Telescopes and Instrumentation 2010: Optical, Infrared, and Millimeter Wave, 77310J (5 August 2010); doi: 10.1117/12.853591
Show Author Affiliations
P. Guillard, Spitzer Science Ctr., California Institute of Technology (United States)
Institut d'Astrophysique Spatiale, CNRS, Univ. Paris Sud 11 (France)
T. Rodet, Lab. des Signaux et Systèmes, CNRS, Univ. Paris Sud 11 (France)
S. Ronayette, Lab. d'Astrophysique, Instrumentation et Modélisation, CEA/IRFU, Univ. Paris-Diderot, CNRS/INSU, CEA (France)
J. Amiaux, Lab. d'Astrophysique, Instrumentation et Modélisation, CEA/IRFU, Univ. Paris-Diderot, CNRS/INSU, CEA (France)
A. Abergel, Institut d'Astrophysique Spatiale, CNRS, Univ. Paris 11 (France)
V. Moreau, Lab. d'Astrophysique, Instrumentation et Modélisation, CEA/IRFU, Univ. Paris-Diderot, CNRS/INSU, CEA (France)
J. L. Augueres, Lab. d'Astrophysique, Instrumentation et Modélisation, CEA/IRFU, Univ. Paris-Diderot, CNRS/INSU, CEA (France)
A. Bensalem, Lab. d'Astrophysique, Instrumentation et Modélisation, CEA/IRFU, Univ. Paris-Diderot, CNRS/INSU, CEA (France)
T. Orduna, Lab. d'Astrophysique, Instrumentation et Modélisation, CEA/IRFU, Univ. Paris-Diderot, CNRS/INSU, CEA (France)
C. Nehmé, Lab. d'Astrophysique, Instrumentation et Modélisation, CEA/IRFU, Univ. Paris-Diderot, CNRS/INSU, CEA (France)
A. R. Belu, Lab. d'Astrophysique, Instrumentation et Modélisation, CEA/IRFU, Univ. Paris-Diderot, CNRS/INSU, CEA (France)
E. Pantin, Lab. d'Astrophysique, Instrumentation et Modélisation, CEA/IRFU, Univ. Paris-Diderot, CNRS/INSU, CEA (France)
P.-O. Lagage, Lab. d'Astrophysique, Instrumentation et Modélisation, CEA/IRFU, Univ. Paris-Diderot, CNRS/INSU, CEA (France)
Y. Longval, Institut d'Astrophysique Spatiale, CNRS, Univ. Paris 11 (France)
A. C. H. Glasse, UK Astronomy Technology Ctr. (United Kingdom)
P. Bouchet, Lab. d'Astrophysique, Instrumentation et Modélisation, CEA/IRFU, Univ. Paris-Diderot, CNRS/INSU, CEA (France)
C. Cavarroc, Institut d'Astrophysique Spatiale, CNRS, Univ. Paris 11 (France)
D. Dubreuil, Lab. d'Astrophysique, Instrumentation et Modélisation, CEA/IRFU, Univ. Paris-Diderot, CNRS/INSU, CEA (France)
S. Kendrew, Leiden Univ. (Netherlands)


Published in SPIE Proceedings Vol. 7731:
Space Telescopes and Instrumentation 2010: Optical, Infrared, and Millimeter Wave
Jacobus M. Oschmann; Mark C. Clampin; Howard A. MacEwen, Editor(s)

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