Optical design of the NSLS-II metrology beamline

The article describes the optical design of the NSLS-II test beamline, dedicated to at-wavelength metrology, in situ surface figuring, crystal optics, radiometry, detectors and instrumentation testing. A key aspect of the beamline design is configuration flexibility, providing as wide as possible range of photon energy, beam size, and divergence, including the optimum trading of SR flux to a required degree of coherence. For this application we propose to use the chromatic properties of compound refractive lens (for hard x-ray) or zone plate (for soft x-ray) to provide band-pass energy filtering and variable spatial coherence. Using such a scheme, it is possible to efficiently vary the transverse coherence from 10 μm to 10 mm at ∼1% monochromaticity. The flux extracted permits real-time phase imaging and at-wavelength metrology, even at the bending magnet beamline.