Custom Superprecise Mirror Arrives at European XFEL

X-ray laser research facility European XFEL has received a 95-cm-long mirror reported to be the most precise of its kind ever built. The mirror’s production is the culmination of a lengthy R&D process involving institutes and companies in Japan, France, Italy and Germany.

The mirror is superflat and does not deviate from its surface quality by more than 1 nm, and is one of several required to allow scientists to use what will be the world’s brightest x-ray laser light for research into ultrafast chemical processes, complex molecular structures and extreme states of matter. The first delivered mirror will be used to filter light.

European XFEL scientist Maurizio Vannoni inspects the delivered superflat mirror, which does not deviate from a perfect surface by more than 1 nm. Courtesy of European XFEL.

The mirror body, with a 95-cm-long and 5.2-cm-wide reflective face, is made from a single crystal of silicon crafted by industrial partners in France and Italy. To polish a mirror to European XFEL’s nanometer specification, optics firm JTEC Corp. in Osaka, Japan, used a new polishing method using a pressurized fluid bath capable of stripping atom-thick layers off of the crystal. The polishing technique alone took nearly a year to develop to a point where the extreme quality could be reached.

Other mirrors in this series will be used to deflect the x-rays by up to a few tenths of a degree into the European XFEL’s six scientific instruments in its underground experiment hall in Schenefeld, Germany. The instruments, which are situated parallel to each other, will eventually be able to operate in parallel, enabling scientists to have greater access to the facility and its unique x-ray light. Similar mirrors will focus the x-ray light within some of the facility’s instruments.

The mirror will be measured at European XFEL and Helmholtz Zentrum Berlin for additional verification of its specifications.