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 (1st order): 443-519 & 561-632 Å

– Total optical length: 1400 mm

Future Design Plans (in response to earlier discussions)

• Add a 3rd 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• RI / RO 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 GmbHGrating Technology 

Dr. Ralf LenkeDr. Klaus Heidemann 

Date August 25, 2004Ref. No. TG04-108 Page 2/4

The 1st order groove efficiency is calculated in a first approache from the averaged groove profile. 

[nm] EFFgr [%]

50.0 64.8 52.5 65.6 55.0 65.8 57.5 65.3 60.0 64.3 62.5 62.9 65.0 61.3

Groove profile 

Position [mm] Blaze angle Anti-blaze angle y z [deg] [deg]

mean 3.4 16.2 +0.3/-0.4 +1.4/-1.3