Fabrication of damage-free Johansson-type doubly curved crystal spectrometer substrate by numerically controlled local wet etching

A doubly curved crystal spectrometer with Johansson-type geometry is very effective for focusing and monochromatizing an X-ray beam. In this study, numerically controlled local wet etching (NC-LWE) was used to form the curvature of the Si(1 1 1) substrate. NC-LWE figuring reduced the inclination of the crystal plane to less than 0.01° by applying the controlled etching of the surface, and achieved error of the figured curvature radius R of 6.7%. The reflectivity and the full width at half maximum (FWHM) of the rocking curve of the processed surface were almost the same as those of the unprocessed surface.