Ultimate spectral purity of the tender X-ray radiation diffracted from a wideband multilayer coated blazed grating.

What we believe to be a novel approach is proposed and theoretically justified to achieve the extremely high spectral purity and high diffraction efficiency of a wideband multilayer-coated blazed grating (BMG) in the tender X-ray range (2.5-3 keV photon energy). The key feature consists of depositing a 70 nm thick B4C film on the BMG surface with subsequent removal of the saw-tooth relief by polishing. Such a design allows suppressing the low-energy parasitic radiation intensity by a factor exceeding 104 on the grating surface through reflection from the film in the total external reflection conditions. A high diffraction efficiency of 8-21% for the -2nd order can be achieved at the same time.