The Extreme Ultraviolet Explorer Spectrometer: Performance Characteristics Based On Development Of The Collimator, Variable Line Space Gratings, Telescope And Detectors

Abstract

We review the design of the spectrometers included on the Extreme Ultraviolet Explorer (EUVE) astronomical satellite. The spectrometer design is novel, consisting of three variable line space reflecting gratings mounted in a slitless configuration behind a grazing incidence telescope. A collimator is employed to reduce diffuse background radiation to negligible lev-els. Prototype gratings have been mechanically ruled and the best samples recover over 80% of the theoretical efficiency of perfectly formed grooves, reaching 30% absolute at 114Å. Groove profile measurements made using a Talystep profilometer and electron micrographs are compared, and found to agree with the blaze angles derived from reflectivity measure-ments. In the final design, grating blaze angles have been optimized to minimize second order contamination. Prototype collimator EUV measurements show peak transmission of 90% of theoretical, with transmission outside the main lobe of less than 0.5%, and a scattering level less than 10^-4arcmin^-1. Using measured performance characteristics of the collimator, telescope, gratings and detector, we have determined the sensitivity of the instrument for a 40,000 sec observation; the average 3-σ sensitivity of continuum flux is approximately 2x10^-27erg/cm²/sec/Hz. This is a factor of 100 dimmer than a bright known EUV source, and is comparable to the sensitivity of the all-sky survey which will be carried out on the EUVE.