Experimental and Theoretical Properties of X-Ray Transmission Gratings

With the advent of X-ray imaging telescopes, high-resolution cosmic X-ray spectroscopy will become an important discipline. X-ray transmission gratings are currently being developed which will be employed as dispersive devices behind a Wolter Type I telescope. These gratings will be assembled from a large number of plane grating facets. This communication describes the experimental properties of individual grating facets and the theoretical properties of complete gratings. In particular, a coma-free curved grating is discussed which may be assembled from facets of identical grating period.