Abstract
High-quality metrology with synchrotron radiation requires in particular a very high spectral purity of the incident beam. This is usually achieved by a set of transmission filters with suitable absorption edges to suppress high-order radiation of the monochromator. The at-wavelength metrology station at a BESSY-II bending-magnet collimated plane-grating monochromator (c-PGM) beamline has recently commissioned a high-order suppression system (HiOS) based on four reflections from mirrors which can be inserted into the beam path. Two pairs of mirrors are aligned parallel so as not to disturb the original beam path and are rotated clockwise and counter-clockwise. Three sets of coatings are available for the different energy ranges and the incidence angle is freely tunable to find the optimum figure of merit for maximum suppression at maximum transmission for each photon energy required. Measured performance results of the HiOS for the EUV and XUV range are compared with simulations, and applications are discussed.
Highlights
Extreme ultraviolet (EUV) and soft X-ray (XUV) optics are in great demand more than ever due to significant developments in areas like EUV photolithography, X-ray/ XUV gratings, space observation and tabletop XUV experiments (Barreaux et al, 2017; Huang et al, 2017; Muller et al, 2017; Naujok et al, 2016; Firsov et al, 2013)
In order to support our in-house developments on new concepts of XUV optical elements (Hafner et al, 2015; Loechel et al, 2013; Senf et al, 2016; Chkhalo et al, 2017; Braig et al, 2017; Siewert et al, 2018; Erko et al, 2010), a versatile UHV reflectometer has been permanently installed as an endstation at the optics beamline at the BESSY-II synchrotron radiation source
The design of the optics beamline as a collimated plane-grating monochromator mount (c-PGM) with a variable incidence angle pre-mirror has addressed all requirements for at-wavelength reflectometry: the beamline offers a broad photon energy range with energy resolution E/ÁE $ 1000–5000, flexible operation of the PGM in highresolution, high-flux or high spectral purity mode, low divergence, sub-millimetre focus size, stray and scattered light suppression via aperture systems and the possibility to steer
Summary
Extreme ultraviolet (EUV) and soft X-ray (XUV) optics are in great demand more than ever due to significant developments in areas like EUV photolithography, X-ray/ XUV gratings, space observation and tabletop XUV experiments (Barreaux et al, 2017; Huang et al, 2017; Muller et al, 2017; Naujok et al, 2016; Firsov et al, 2013). The design of the optics beamline as a collimated plane-grating monochromator mount (c-PGM) with a variable incidence angle pre-mirror has addressed all requirements for at-wavelength reflectometry: the beamline offers a broad photon energy range with energy resolution E/ÁE $ 1000–5000, flexible operation of the PGM in highresolution, high-flux or high spectral purity mode, low divergence, sub-millimetre focus size, stray and scattered light suppression via aperture systems and the possibility to steer. The HiOS is based on four mirrors that are inserted into the beam path without net deflection of the beam trajectory These two systems in the optics beamline provide a wide flexibility for light shaping upstream of the reflectometer; the properly aligned HiOS is by far more effective than the filter units (Schafers et al, 2016). A double set of pinholes and apertures installed in front of the reflectometer provides efficient stray light and scattered
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