Siewert, F.: Metrology, Mirrors and Gratings - Advances and Challenges in Synchrotron Optics. Journal of Physics: Conference Series 425 (2013), p. 152001/1-6
10.1088/1742-6596/425/15/152001
Open Access Version
Abstract:
Ultra-precise reflective and diffractive optical elements like blazed diffraction gratings or ultra-precise mirrors of flat, elliptic, parabolic, or other shapes have become key components in today’s synchrotron optics. These optical components feature nanometre accuracy on a macroscopic length scale. Beamlines with extreme lengths of 100m to 1km or more (as planned for the European XFEL) will require plane mirrors characterized by a residual slope error of 50nrad rms and a curvature radius of > 1000km on a length of 800mm or even more. Diffraction limited focusing mirrors for hard X-ray application show residual slope deviations of 50nrad rms on a length of 350mm. The current slope limit for focusing mirrors in VUV-application lies at around 0.5µrad rms, one order of magnitude inferior compared to hard X-ray focusing optics, and it can still not be exceeded due to technological restrictions. The requirements for diffraction gratings are even more challenging. In addition to the challenges posed by perfect substrate quality, special attention is needed to guaranty a precise positioning of the grooves along the full aperture length. A positioning accuracy of about 20nm for the carriage system of a ruling engine is mandatory to meet the Marechal tolerance for gratings. For the manufacture of blazed and laminar gratings, we are currently establishing a new technological laboratory at the Helmholtz Zentrum Berlin (HZB), including instrumentation from Carl Zeiss. Besides the present Zeiss technology, we are also developing an advanced technology line, including a new ultra-precise ruling machine, ion etching technology as well as laser holography.