We describe the design and performance of the Medium Resolution Spectrometer (MRS) for the JWST-MIRI instrument. The MRS incorporates four coaxial spectral channels in a compact opto-mechanical layout that generates spectral images over fields of view up to 7.7 X 7.7 arcseconds in extent and at spectral resolving powers ranging from 1,300 to 3,700. Each channel includes an all-reflective integral field unit (IFU): an 'image slicer' that reformats the input field for presentation to a grating spectrometer. Two 1024 X 1024 focal plane arrays record the output spectral images with an instantaneous spectral coverage of approximately one third of the full wavelength range of each channel. The full 5 to 28.5 micron spectrum is then obtained by making three exposures using gratings and pass-band-determining filters that are selected using just two three-position mechanisms. The expected on-orbit optical performance is presented, based on testing of the MIRI Flight Model and including spectral and spatial coverage and resolution. The point spread function of the reconstructed images is shown to be diffraction limited and the optical transmission is shown to be consistent with the design expectations.
@article{arxiv.1508.03070,
title = {The Mid-Infrared Instrument for the James Webb Space Telescope, VI: The Medium Resolution Spectrometer},
author = {Martyn Wells and J. -W. Pel and Alistair Glasse and G. S. Wright and Gabby Aitink-Kroes and Ruyman Azzollini and Steven Beard and B. R. Brandl and Angus Gallie and V. C. Geers and A. M. Glauser and Peter Hastings and Th. Henning and Rieks Jager and K. Justtanont and Bob Kruizinga and Fred Lahuis and David Lee and I. Martinez-Delgado and J. R. Martinez-Galarza and M. Meijers and Jane E. Morrison and Friedrich Mueller and Thodori Nakos and Brian O'Sullivan and Ad Oudenhuysen and P. Parr-Burman and Evert Pauwels and R. -R. Rohloff and Eva Schmalzl and Jon Sykes and M. P. Thelen and E. F. van Dishoeck and Bart Vandenbussche and Lars B. Venema and Huib Visser and L. B. F. M. Waters and David Wright},
journal= {arXiv preprint arXiv:1508.03070},
year = {2015}
}