title: Optical design of a high-spatial-resolution extreme-ultraviolet spectroheliograph for the transition region.
abstract: A spectroheliograph dedicated to the observation of the solar disk in the extreme-ultraviolet OV spectral line at 62.97 nm is described. As demonstrated in the Skylab SO-82A spectroheliograph [Appl. Opt. 16, 870 (1977)], this line is uniquely suited to characterize solar plasma in the important 250, 000 K temperature regime. No multilayer coating or suitable filter is yet available to select this wavelength, so an optical design based on a double spectrograph with a spatial filter to remove the unwanted radiation has been developed. Analysis of the optical design shows that this instrument can obtain a 1 arcsec spatial resolution (two pixels) with a relatively high image-acquisition cadence. A preliminary tolerance analysis has been performed. A simple method of instrument alignment in visible light is also described.
authors.affiliation: Dipartimento di Ingegneria dell'Informazione, Università di Padova, Via Gradenigo 6/B, I-35131 Padova PD, Italy. naletto@dei.unipd.it
authors.forename: Giampiero
authors.initials: G
authors.lastname: Naletto
authors.forename: Silvano
authors.initials: S
authors.lastname: Fineschi
authors.forename: Ester
authors.initials: E
authors.lastname: Antonucci
authors.forename: Vania
authors.initials: V
authors.lastname: Da Deppo
authors.forename: Piergiorgio
authors.initials: P
authors.lastname: Nicolosi
authors.forename: Luca
authors.initials: L
authors.lastname: Zangrilli
authors.forename: Marco
authors.initials: M
authors.lastname: Romoli
authors.forename: Marco
authors.initials: M
authors.lastname: Malvezzi
authors.forename: Daniel
authors.initials: D
authors.lastname: Moses