The toroidal diffraction grating for the HiRES spectrometer: effect of potting on surface figure

Abstract

The high resolution stigmatic extreme ultraviolet spectroheliometer (HiRES) rocket payload employs a toroidal diffraction grating as the dispersing element in its spectrometer. Such a grating produces stigmatic images (free from astigmatism) of the sun at several different wavelengths, which are determined by the grating's geometry. For this paper, the aspect ratio of the grating was determined both before and after it was potted--a mounting procedure in which the grating element is in encased in silicon adhesive; the effect of this upon the figure of the grating being previously unknown. A change in the surface figure would mean the highest quality images for a given angle of incidence would be produced at different wavelengths than those anticipated.