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Abstract
X-ray emission spectroscopy (XES) is a powerful tool for electronic structures characterization of materials widely applied in the study of 3d elements. The von Hamos and Johann spectrometers currently installed at the FXE instrument operate in Bragg reflective geometry have been successfully supporting user experiments. However, their efficiency drops quickly at energies > 15 keV, significantly restricting the science cases for spectroscopy on heavier elements, e.g., 4d metals. Moreover, XAS at high X-ray energies is strongly limited by the large core-hole lifetime broadening, wherein an efficient X-ray spectrometer is necessary for high resolution detection mode. In order to overcome these limitations a new High Energy Laue X-ray Emission Spectrometer is being developed at FXE. Extensive X-ray tracing simulations guided the design of new statically-bent Laue analyzers with shorter radius of curvature aiming at improved efficiency and maintaining an energy resolution on the order of the core-hole lifetime of 4d metals. The possibility of dispersive operation was also investigate by the tracing simulations. One new silicon analyzer was recently tested at SuperXAS beamline at the Swiss Light Source. In terms of energy resolution, our Si(111)3 Laue analyzer provided a ΔE~3.5×10-4, limited by the 100 μm beam size. Better resolution is expected at FXE where the beam size is 40-50 μm at 20 keV. A set of measurements detecting the Kβ1,3 and VtC XES of several niobium samples was also performed, confirming the dispersive capabilities of our new Laue analyzers is sufficient to detect an energy interval of ~80 eV. With the modest flux of SuperXAS (~1011 photons/sec[4]) a detector image of the Nb Kβ1,3 emission is visible in as little as 10 secs and the VtC line in about 1 mins. Considering that the European XFEL routinely provides an equivalent of ~1011 photons in a single pulse, FXE will be able to provide excellent pump-probe spectroscopic capabilities in 15-20 keV range, covering the K lines of 4d elements and L lines of 5f elements. The first commissioning campaign of the HELIOS spectrometer will happen in the first semester of 2023.