Mechanical challenges for wavefront preserving optics

Mr Olivier Hignette, Xoptronics

Abstract
The availability of a few tenths of microradian optical elements and low emittance of third generation synchrotron X-ray sources allow science applications like nanofocusing or phase imaging. Mechanical engineering must be capable to placing dynamically the sample with respect to the source within a few tens of nanoradians and nanometers. In order to preserve the coherence of the X-ray beam wavefront, the tolerances on the tilt and curvature of reflective and diffractive surfaces are challenging. As an example, for a 12 Kev energy and a 0.5 mm aperture, the tilt drift is to be constant within 25 nanoradians and the additional wavefront radius of curvature is to be larger than 100 Km. We shall explore crystal and mirror systems designs and tolerances . Some criteria will be provided to choose between static and closed loop designs. A review of state of the art X-ray beam position monitors, optoelectronic and survey sensors will be presented, with corresponding measuring Beamlines architectures. What is to be most critically measured: position, angle or curvature, with respect to which intermediate references (slabs)? The merits of fixed curvature versus dynamically bent systems are presented, with trade-off between long term stability and fine curvature tuning capability. The principles of bender systems are reviewed, with attention on acceptance tests issues and thermal aspects in UHV.