Hard X-ray multilayer mirror round-robin on the wavefront preservation capabilities of W/B4C coatings

Abstract

A round-robin between the multilayer deposition laboratories of the Advanced Photon Source, the European Synchrotron Radiation Facility and the National Synchrotron Light Source II has been initiated in order to study standard W/B4C multilayer mirrors produced by the different facilities. The use of such multilayer mirrors for hard X-ray monochromatisation represents an important alternative to crystal-based devices when greater photon flux density is desirable for, e.g., X-ray imaging applications and other photon-intensive techniques. Currently, knowledge about the potential degradation of the wavefront in terms of beam profile distortion and coherence properties due to reflection on a multilayer mirror is limited. In order to address this issue, the beam profile and coherence properties of a monochromatic synchrotron beam reflected by the individual mirrors were studied at the Advanced Photon Source insertion device beamline 32-ID. The results indicate that by using the same coating material, commercially available high quality substrates and a similar coating technique, mirrors with comparable performance can be produced with quite different multilayer deposition facilities. Furthermore, no wave-optical formalism is available at this time which relates the influence of a multilayer reflection on the wavefront to the structural quality of the mirror. Hence, the experimental studies presented are highly targeted in order to identify parameters which have a potential influence on the wavefront preservation properties of a multilayer.