ESRF metrology laboratory: overview of instrumentation,measurement techniques and data analysis

摘要

The ESRF has initiated an ambitious ten-year upgrade program involving the construction of eight new beamlines and significant refurbishment of existing instruments. The availability of high-precision X-ray optical elements will be a key factor in ensuring the successful implementation of these beamline projects. Particular challenges are to ensure the necessary optical quality for X-ray beam coherence preservation and high numerical-aperture high focusing systems. Surface optical metrology is a key tool, not only for the quality control, but also in improving the manufacturing processes of such components. Amongst the most demanding tasks is the characterisation of the surface topography of highly aspheric surfaces for reflective nanofocusing technologies which typically require measurement of shape errors in the nm range. In order to satisfy these new demands, the ESRF metrology laboratory has recently been equipped with two new instruments: a Fizeau interferometer and a micro-interferometer. In parallel the long trace profiler has been continuously developed to increase both stability and accuracy. In this paper we will present the new instrumentation and associated techniques like micro-stitching interferometry used to measure typical high quality X-ray mirrors. We will also focus on the parameters that can affect repeatability and accuracy of the radius of curvature assessment of flat optical surfaces, in particular when measuring with the long trace profiler. Finally an example of the power spectral density function based on our instrument measurements of a typical high quality x-ray mirror will be shown.