Design and realization of a grazing-incidence plane-grating monochromator

The design and realization of a plane-grating monochromator mainly intended for high-energy resolution in the extreme-ultraviolet and soft-X-ray spectral regions is presented. The principal application is the spectral selection of high-order laser harmonics generated in gas combined with the possibility to achieve sub-20-meV bandwidth, approaching synchrotron-like beamlines resolution performances. This geometry has three optical elements: a uniform-line-spaced plane grating illuminated by the converging light coming from a focusing cylindrical mirror and an additional plane mirror that is needed to change the grating subtended angle to keep the system in focus on a fixed slit. The parameters of the focusing mirror are determined to introduce a coma that compensates for the coma given by the grating. A monochromator for the 12-50 eV region has been realized to show the feasibility and the performances of the configuration.