Superfinish technology for enhanced grazing incidence reflectivity in x-ray telescopes

High performance x-ray Wolter I telescopes require especially at high energies excellent specular mirror shell reflectivity features to collect grazing incidence radiation. Applying galvanoplastic techniques the surface quality of complementary mandrels can be replicated on the mirror shells with negligible degradation only. Therefore, adequate surface finish by advanced superpolishing of the mandrels is a strong prerequisite in order to improve the specularly reflected portion of the incoming x-ray light. For that reason, a new surface technology was developed within the frame of the JET-X mirror assembly project providing reduced high frequency components of the surface roughness correlated with the reduction of mandrel surface scattering (diffuse reflection). At high x-ray energies (8.1 keV) the measured encircled energy image of mirror shells replicated from these mandrels was up to 3 times better than from untreated mandrels.