High-frequency low-blaze-angle Mo/Be diffraction gratings – efficiency study

The paper presents the results of studies of the diffraction efficiency of blazed gratings, carried out by modelling in the PCGrate$^{\mathrm{TM}}$ code using groove profile shapes obtained by atomic force microscopy and measurements on the laboratory reflectometer with a high-resolution Czerny-Turner spectrometer. High-frequency diffraction gratings with a density of 2500 mm$^{-1}$ and a small inclination angle of the reflecting facet were fabricated on Si(111)1.8$^\circ$ wafers using electron beam lithography and anisotropic wet etching. A grating with a blaze angle of $\sim$1.7$^\circ$, coated with 40 Mo/Be bilayers, demonstrated in the classical mount an absolute diffraction efficiency of $\sim$38% in minus second order at an incident angle of 3$^\circ$ of unpolarized radiation at a wavelength of 11.3 nm. Taking into account the measured reflectance of the multilayer coating $\sim$0.6, the maximum relative (grating) efficiency was $\sim$63%.