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.
Alignment methods for ultraprecise deflectometric flatness metrology
At the Physikalisch-Technische Bundesanstalt (PTB) two new scanning deflectometric systems (Deflectometric Flatness Reference: DFR) were installed for measuring topographies of nearly flat surfaces with sub-nanometre uncertainty. The two systems can measure the form of horizontally and vertically orientated specimens with a diameter of up to 700 mm. The systems are based on different deflectometric procedures, the so-called direct and the difference deflectometry. With the flatness measuring systems, an uncertainty down to 0.1 nm (depending on the specimen and its peak-to-valley) is being aimed at for the 95% coverage interval. Virtual experiments show that the optical and mechanical components must be aligned in the arcsecond range in order to achieve errors for the topography in the sub-nanometre range. In this paper we describe the setup of the new DFR system for horizontally orientated specimens in detail and show methods and experimental results for an accurate alignment of the optical and mechanical components. We present an accurate alignment strategy for ultraprecise deflectometric measurements and show a measurement of a section at a horizontally orientated specimen.
Prediction of net pressure on pressure equalized cavities
Abstract A numerical model has been developed for prediction of net pressure on pressure equalized cavities. The results based on this model show good agreement with those obtained from mock-up tests. Parametric studies verify that reductions in cladding load are possible, with proper design of curtain walls.