Grazing Incidence XUV Spectroheliograph RES-C for the CORONAS-I Mission

The RES-C grazing incidence XUV spectroheliograph has been developed in the P. N. Lebedev Physical Institute (FIAN) as a part of the CORONAS-I project. Its objective is to obtain images of the full Sun in monochromatic lines over the spectral range of 180–210Å, which includes prominent emission from ions of Fe VIII–Fe~XIII, O VI, and Fe XXIV. Here, we describe the optical scheme of the spectroheliograph, and show results of XUV testing of its individual component elements as well as of the complete assembled instrument. XUV measurements were made of the absolute diffraction efficiency and stray-light level for both holographic and mechanically ruled gratings, the spectral reflectivity of the multilayer-coated mirrors, the transmittance of the thin aluminum blocking filters, and the combined spectral efficiency of the whole instrument. The spectral and spatial resolutions of the spectroheliograph were measured by recording spectrally dispersed images of a laser plasma source in monochromatic lines of fluorine ions between 185–200Å. For comparison, we also present spectral images of the Sun obtained with the spectroheliograph as flown on the CORONAS-I satellite mission.