Normal-Incidence Design Option for SolO/EUS Roger J. Thomas NASA/GSFC 2004 November 04

NEXUS : SmEx Proposal Required EUV spectrograph capabilities –Rapid cadence (10s) –Large FOV –Wide temperature coverage: 20,000 K to 4 MK –Doppler measurements of 1-5 km/s –1.2 arcsec spatial resolution

NEXUS : SmEx Phase-A Design Basic components of NEXUS –2 element normal-incidence optical design –Off-axis parabolic mirror telescope f/9.3 –Toroidal varied-line-space (TVLS) grating spectrograph with a magnification of 5.6 –B4C / Iridium optical coatings –Slit (0.5 arcsec) / Slot (1 arcmin) –Two ICCD detectors –Wavelength ranges (1 st order): & Å –Total optical length: 1400 mm

Future Design Plans (in response to earlier discussions) Add a 3 rd wavelength bandpass Allow telescope to be slightly Hyperbolic Increase FOV and spectral coverage Relax spatial & spectral resolutions Increase entrance-slit width Reduce physical instrument dimensions

Design Considerations Magnifying spectrograph R I / R O  4 Large plate scale in small physical length Most efficient use of available volume Aberrations corrected by VLS rulings on Ellipsoid Thermal advantages All optics see un-concentrated solar radiation Primary at back: allows shielding and direct radiative cooling Unwanted light can be reflected out the front

EUNIS/NEXUS TVLS Grating -- Zeiss Measured Groove-Density Variations

EUNIS/NEXUS TVLS Grating -- Zeiss Measured Groove-Profiles

NASA-Goddard Space Flight Center Dr. Roger Thomas TVLS Grating #G5 for EUNIS #3 Carl Zeiss Laser Optics GmbH Grating Technology Dr. Ralf Lenke Dr. Klaus Heidemann Date August 25, 2004 Ref. No. TG Page 2/4 The 1 st order groove efficiency is calculated in a first approache from the averaged groove profile. [nm] EFFgr [%] Groove profile Position [mm] Blaze angle Anti-blaze angle y z [deg] [deg] mean / /-1.3