As dispersing elements, grazing incidence reflection gratings offer the unique combination of high dispersion and wide spectral coverage at high efficiency. They can therefore be coupled with large area, low-resolution mirrors and high quantum efficiency detectors to yield moderate resolution spectroscopy of faint X-ray sources. Various design options are presented and compared, including both objective and convergent-beam configurations and both in-plane and off-plane grating mountings. A specific reflection grating payload design for ESA’s X-Ray Multi-Mirror Mission (XMM) is reviewed in more detail. Predicted performance curves derived from ray trace studies are presented along with preliminary X-ray reflectivity measurements of prototype grating samples.

The Diffuse X-ray Spectrometer (DXS) experiment is part of NASA’s SHEAL 2 mission, scheduled to be flown as an attached Shuttle payload in 1992. The DXS is designed to measure the spectrum of the low energy (0.15 to 0.28 keV) diffuse x-ray background with energy resolution better than 0.01 keV. This paper describes the DXS experiment and presents the results of calculations of the anticipated data.

A concept of stigmatic spectroscopic instruments for the range λ ~30-300 Å is presented, A parallel beam is dispersed by means of a plane diffraction grating at grazing incidence, whereas focusing of the XUV radiation is performed by a concave multilayer mirror at normal incidence. A spectroheliograph of the new type may have dispersion an order of magnitude higher than traditional Wadsworth-type instruments. The theoretical resolving power of a spectrograph of the new type is limited by apertures of the multilayer mirrors or by the total number of grooves of the grating and many reach (λ/δλ)theor ~ mN ~ 3.105 using presently available optical elements.