Wadsworth mount redux: paraboloidal versus spherical gratings.
Spherical and paraboloidal diffraction gratings are considered for use on an experiment involving a collection of satelliteborne spectrographs that will investigate astrophysical plasmas in the spectral region from approximately 100 to 300 A. We shall use eight spectrographs: Wadsworth mounts in near-normal incidence with effective focal lengths of 3 m, each centered on a chosen wavelength in this spectral range. Ray tracings show that paraboloidal gratings used in the Wadsworth mount have a significant increase in resolution over spherical gratings of the same effective focal length, used in the same mounting, as long as the spectral ranges are small (approximately 10% of the central wavelength). This increase in resolution is due to the spatial extent of coma for a paraboloidal grating that is less than the circle of least confusion of spherical gratings.
Hunter
William R
WR
SFA, Incorporated, Woodlands Office Center, 9315 Largo Drive West, Suite 200, Largo, Maryland 20774, USA. wrhunter@bellatlantic.net
Kowalski
Michael P
MP
Cruddace
Raymond G
RG