Current status of the NSLS-II optical metrology laboratory

Abstract During the last decade, we have seen an ultra-fast progress in X-ray optics performances. This enhancement is directly linked to the development of the necessary tools to control these optical components. These metrology tools are necessary for the fabrication (to guide some polishing deterministic process) and also for the ultimate characterization used to validate surface parameters (often inside their own mechanical support) prior to installation in a beamline. It is now necessary to characterize optical surface figure, slope errors and roughness on meter-long optics over spatial frequencies as short as 0.1 mm and with slope errors reaching less than 100 nrad rms or surface figure errors close to 1 nm in order to not spoiled and preserve the high brightness made available by third and fourth generation synchrotron/FEL sources like NSLSII or LCLS. For this purpose, the new NSLS-II Optical Metrology Laboratory (NSLSII-OML) includes commercial instruments for measuring long spatial frequency figure errors, mid spatial frequencies and high frequency roughness and had started some R&D activities. The NSLSII-OML foresee some efforts on the development of new instruments for slope errors measurements with the construction of a long trace profiler/NOM that will be able to reach 50 nrad slope error accuracy. Effort towards the construction of new instruments with stitching capabilities using interferometer and Shack Hartmann and software configurable optical test (SCOTS) stations are also under consideration to be able to perform 2D mapping of the optical surfaces in order to feed a deterministic polishing process based on ion beam figuring (under development in collaboration with the NSLS II Optical Fabrication Group). In the same time, it also becomes clear that low emittance and high stability of NSLS-II X-ray beam combined with extended possible beamline offered by large experimental hall may and should be used for the metrology. Approved plan includes the construction of specialized beamline for at-wavelength metrology, radiometry, crystal optic characterization and instrumentation development. This paper provides a brief description of the instruments currently available in the laboratory and gives an overview of the very active R&D efforts within the NSLSII-OML.