X-ray diffraction gratings

An x-ray diffraction grating consisting of a structure having a surface capable of reflecting x-rays, said surface being grooved so that in cross-section the profile of said surface alternates regularly between geometrically similar lines, in which the height of the alternation varies significantly over the area of the surface. The grating may be plane or curved; the variation in height may occur as a single step, a plurality of steps or may be continuous; the variation may occur either transverse to or parallel to the grooving.