Abstract
The surface figure error of a hard X-ray mirror was improved by combining differential deposition and off-line metrology tools. Thin Cr layers were deposited on flat substrates by DC magnetron sputtering. The substrates were moved in front of a beam-defining aperture. The required velocity profile was calculated using a deconvolution algorithm. The Cr thickness profiles were measured directly using hard X-ray reflectivity data. The surface figure was characterized using conventional visible-light metrology instrumentation (long trace profiler) before and after the deposition. The method converges quickly, and after two iterations the mirror surface figure had improved by a factor of 7. The surface roughness evolves with increasing Cr thickness and deteriorates the quality of subsequent multilayer coatings. The mirror curvature can change upon coating, which complicates the interpretation of the surface metrology data. In this context, the role of layer stress is discussed. Potential improvements of the process are also proposed.
Highlights
The performance of reflective X-ray optics, in particular multilayer (ML) coated mirrors, strongly depends on the quality of the underlying substrates (Morawe et al, 2011)
The most prominent methods used for X-ray optics are elastic emission machining (EEM) (Yamauchi et al, 2002), ion beam figuring (IBF) (Arnold et al, 2010; Wang et al, 2019) and differential deposition (DD)
While EEM and IBF rely on material removal, DD adds material via thin-film coating
Summary
The performance of reflective X-ray optics, in particular multilayer (ML) coated mirrors, strongly depends on the quality of the underlying substrates (Morawe et al, 2011). To correct for figure errors at these length scales, precise metrology and deterministic polishing techniques have been developed. The most prominent methods used for X-ray optics are elastic emission machining (EEM) (Yamauchi et al, 2002), ion beam figuring (IBF) (Arnold et al, 2010; Wang et al, 2019) and differential deposition (DD). This work will focus on the correction of medium to long spatialperiod height errors of X-ray mirror substrates with a potential length of up to 1 m. The potential impact of film stress and roughness on the corrected substrates will be discussed and directions for further development will be indicated
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
