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Optical performance of the JWST/MIRI flight model: characterization of the point spread function at high-resolution

Guillard, P. and Rodet, T. and Ronayette, S. and Amiaux, J. and Abergel, A. and Moreau, V. and Augueres, J. L. and Bensalem, A. and Orduna, T. and Nehmé, C. and Belu, A. R. and Pantin, E. and Lagage, P.-O. and Longval, Y. and Glasse, A. C. H. and Bouchet, P. and Cavarroc, C. and Dubreuil, D. and Kendrew, S. (2010) Optical performance of the JWST/MIRI flight model: characterization of the point spread function at high-resolution. In: Space telescopes and instrumentation 2010 : optical, infrared, and millimeter wave. Proceedings of SPIE. No.7731. Society of Photo-optical Instrumentation Engineers (SPIE) , Bellingham, WA, Art. No. 77310J. ISBN 978-0-81948-221-1.

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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.

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Guillard, P.0000-0002-2421-1350
Additional Information:© 2010 SPIE.
Subject Keywords:JWST; MIRI; Infrared; Cryogenic; Microscanning test; PSF
Series Name:Proceedings of SPIE
Issue or Number:7731
Record Number:CaltechAUTHORS:20110321-083305397
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Official Citation: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 and S. Kendrew "Optical performance of the JWST/MIRI flight model: characterization of the point spread function at high resolution", Proc. SPIE 7731, Space Telescopes and Instrumentation 2010: Optical, Infrared, and Millimeter Wave, 77310J (August 04, 2010); doi:10.1117/12.853591;
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:22997
Deposited By: Tony Diaz
Deposited On:21 Mar 2011 21:07
Last Modified:09 Mar 2020 13:18

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