Surface engineering and advanced coatings for the next generation of X-ray diffractive optics - XOPTICS

Project summary

The proposed project is aimed to develop and further refine crucial fabrication steps of high-end X-ray diffraction optics. The nowadays X-ray optics has to fulfill very tight specifications regarding the surface finish, surface roughness and sub-surface crystal quality. The surface figure has to be better than lambda/20 measured by reflected wave distortion at HeNe laser wavelength. The surface roughness has to be lower than 0.1 nm RMS. And the sub-surface damage (SSD) to the crystal lattice introduced by surface manufacturing technique has to be removed. The conventional surface cutting, milling, grinding, lapping and polishing techniques are suitable only for planar or symmetric surfaces. However the latest developments in the X-ray diffraction optics involve fabrication of complicated symmetric and asymmetric channel-cuts where the active surfaces are not accessible by conventional surface manufacturing and polishing techniques. In the last thirty years the ultra-precision manufacturing using diamond tools was established as a promising manufacturing technique. This technique coined as single point diamond turning (SPDT) can manufacture precise interfaces with very low figure error and surface roughness less than 1 nm RMS. This project targets the refinement of SPDT manufacturing technique intending to reach the lowest possible SSD. The manufacturing optimization cycles will be supported by measurements and numerical simulations of residual stress introduced by SPDT. In order to make the SPDT compatible with the fabrication of the latest high-end X-ray optics additional polishing steps has to be developed especially for the nested surfaces. The aim of this project is to refine the existing polishing techniques in combination with SPDT. A special goal is the development of new polishing approaches. Especially we will address the combination of SPDT manufacturing with ion beam polishing and nanosecond laser remelting technologies. Furthermore we will develop wear and oxidation resistant functional coatings that will suppress X-ray scattering at low incidence/exit angles.