Fabrication and study of a concave crystal mirror for the KORTES project

A method for fabrication of a concave spherical mirror made of crystalline quartz is proposed and X-ray optical properties of the mirror are studied. The radius of curvature is 1630 mm. The shape of the mirror surface is studied using an interferometer with a diffraction reference wave. In the entire processing region, the maximum deviation from the nearest sphere is about 0.2 $\mu$m and the rms is 34 nm, so that high quality of imaging is provided with an angular error of about 2" (angular seconds). Reflection coefficient (about 7%) and lower bound limit of spectral selectivity ($\lambda/\delta\lambda\approx$ 1775) are determined in the vicinity of a wavelength of $\lambda$ = 0.834 nm, which is close to the working wavelengths of the MgXII doublet ($\lambda$ = 0.8418 and 0.8423 nm). Position of the Bragg peak and spectral selectivity remain unchanged upon bending of the crystal mirror within measurement accuracy.