Pushing the limits: latest developments in angle metrology for the inspection of ultra-precise synchrotron optics

The requirements on the quality of ultra-precise X-ray optical components for application in the Synchrotron Radiation (SR) community are increasing continually and strongly depend on the quality of the metrology devices available to measure such optics. To meet the upcoming accuracy goal of 50 nrad rms for slope measuring profilers, a dedicated project, SIB58 Angles, consisting of 16 worldwide partners and supported by the European Metrology Research Programme (EMRP) was started in Sep 2013. The project covers investigations on autocollimators under extremely challenging measuring conditions, ray-tracing models, 2D autocollimator calibration (for the first time worldwide), determination of error sources in angle encoders providing traceability by ‘sub-division of 2π rad’ with nrad uncertainty, angle generation by 'ratio of two lengths' in nrad level, and on the development of portable precise Small Angle Generators (SAGs) for regular in-situ checks of autocollimators’ performance. Highlights from the project will be reported in the paper and the community of metrology for X-Ray and EUV Optics will be informed about its progress and the latest work in angle metrology.