Holographic gratings for the Far Ultraviolet Spectroscopic Explorer: development, imaging, and efficiency tests of...

We report on a study and test of two 6000-groove/mm prototype holographic gratings for NASA's FarUltraviolet Spectroscopic Explorer (FUSE) mission. The first grating was designed and developed onthe basis of the FUSE requirements as specified at the end of the first study in 1992. This design relieson an ellipsoidal grating, recorded with aberrated wave fronts to correct sagittal coma. The secondgrating corresponds to the new design adopted after the complete mission was restructured in1993. With this solution a new family of spherical holographic gratings recorded with stigmaticsources was permitted to increase the aperture size while simplifying the figuring and recording of theblank. The design, fabrication, and testing of each prototype are described, and we show that thechallenging requirement of a 30,000 resolving power at 1000 Å, with a 25% groove efficiency, is reached.