Atomic-level polishing of x-ray mirrors using PMMA and water

Abstract

X-ray focusing mirrors require nanometer-level figure accuracy and sub-nanometer surface roughness to preserve the x-ray wavefront and achieve high-performance focusing. To meet these stringent requirements, we investigated an alternative polishing approach using organic polymer tools. Among the tested polymers, polymethyl methacrylate (PMMA) exhibited the highest material-removal rate for synthetic quartz in pure water. Based on this finding, we developed Water-Based Polishing with an Organic Polymer (WAPOP), an abrasive-free polishing method using water and a PMMA tool, together with an XYZ three-axis scanning system for mirror-scale processing. For a planar quartz x-ray mirror, WAPOP reduced the WLI-measured surface RMS from 0.252 to 0.091nm and the AFM-measured surface roughness from 0.208 to 0.067nm RMS. Subsequent deterministic figure correction by Nozzle-type EEM reduced the representative figure error from 132.208 to 1.887nm PV and from 34.330 to 0.427nm RMS. These results demonstrate that combining WAPOP for atomic-level surface flattening with Nozzle-type EEM for figure correction is an effective approach for fabricating high-quality x-ray mirrors.