Performance of the thin film coating on the long and collimating BEaTriX parabolic mirror

Abstract. Long mirrors coated with thin films are used for a wide range of applications, e.g., focusing or collimating high-energy optics. Focusing of incident x-ray radiation is one of the major applications for high-energy astronomical telescopes, and collimation of divergent x-ray sources is used for experimental setups to confine or expand x-ray radiation. Both applications utilize grazing angle reflection, which is typically enhanced using x-ray reflective thin films. One of the challenges with thin film coatings is the deposition induced nonuniformities. For x-ray reflecting mirrors, nonuniformity in the thin film deposition influences the thickness, roughness, and density of the thin film, which affects the predicted performance of the mirror. As part of the thin film coating development for the 456-mm-long parabolic mirror used in the Beam Expander Testing X-ray facility, our work presents the challenge of coating long x-ray reflective mirrors. We used x-ray reflectometry to investigate the nonuniformity in platinum and chromium thin films deposited using direct current magnetron sputtering.