The concept of a stigmatic flat-field X-ray spectrograph based on conical diffraction

The optical scheme of a flat-field stigmatic X-ray spectrograph, which includes a grazing-incidence focusing mirror and a concave fan-type diffraction grating crossed with respect to the mirror and mounted in a conical diffraction scheme, is calculated analytically. Spectral images of a point monochromatic source are obtained by numerical ray tracing, confirming the high quality of spectral images at a level of 1 x 4 mm. It is assumed that the use of small grazing incidence angles in combination with the application of multilayer reflective coatings, including aperiodic ones, will make it possible to extend the working spectral range of the stigmatic spectrograph to the region of the 'tender' (hw approximate to 1.5 - 6 keV) X-ray range.