super-polished Borkron glass

For particular applications Borkron glass is the preferred material for neutron guides at some neutron scattering facilities. Due to the specific fabrication process the Borkron glass is only available as ingots. The ingots do not have macro- and microscopic smooth surfaces like floated glass. Thus a comprehensive machining is required to obtain glass plates with specifications suitable for the fabrication of neutron guides. The processes for the formatting of the plates provide a high quality in terms of parallelism and planarity which can be translated into highly geometrically accurate neutron guides. However, for a long time the microscopic smoothness (roughness) of the surface of those glass plates was only moderate limiting the reflectivity of the supermirror coatings.
In order to improve the surface roughness SwissNeutronics started a research project to develop the super-polishing of Borkron glass with the aim to obtain atomically smooth surfaces equivalent or better than the inherently very smooth surface of floated glass. Finally a super-polishing process was established achieving the desired performance on the currently typically used types of Borkron glass: N-ZK7 and N-BK7. As a result SwissNeutronics provides neutron guides and optics using super-polished Borkron glass with supermirror coatings having excellent reflectivities equal to the best results on floated glass.