ABSTRACT
X-ray spectroscopy is a domain of greatest interest. The emission and diffraction of X-rays is a powerful tool to analyze the structure of matter and its composition. X-ray analysis is done by recording spectral data, which requires using periodic structures. There are two main types of gratings that operate in the X-ray domain, namely bare metallic gratings and multilayer gratings. First, one can evaporate a multilayer on top of a bare metallic or dielectric profile, and obtain a multilayer coated grating. Second, one can etch a grating inside a flat multilayer and obtain a Bragg grating. The use of gratings under grazing incidence is not a strong handicap in making spectra. However, in many situations, gratings are not only asked to diffract light, but also to focus or collimate it. In the X-ray domain, the result is high aberrations, which are difficult to correct in the sense that they require making grooves on a sophisticated curved surface.
