Schematic depiction of the experimental setup. The RIXS spectrometer is a modified XES 350 with three gratings (only one is drawn here). A MCP detector is operated behind a vacuum separating foil. A differential pumping stage with tubes serving as pin holes is used to decouple the vacuum in the experimental chamber from the beamline vacuum. The coordinate system defines the geometry with x as the propagation direction of the x-ray beam, y as the optical axis of the RIXS spectrometer, and z the propagation direction of the liquid jet. For collinear incoupling of an optical laser we use a setup provided as part of the SXR beamline at LCLS.21
The components of the experimental setup: top view (upper panel) and side view (lower panel).
Calculated photon energy dependence of the combined transmission of the gratings and the C-parylene foil (thickness 234.5 nm). Grating efficiencies were calculated using the REFLEC program.31–33 Data for the transmission of the foil were taken from Ref. 34. Darker curves show transmission without the foil (only grating efficiency).
Schematic geometry of the spectrometer in the meridional plane. The detector position D1 (on the Rowland circle) corresponds to a source position S1 (entrance slit, on the Rowland circle) and detector position D2 (off the Rowland circle) corresponds to a source position S2 (jet, off the Rowland circle). Displacements of the jet from the entrance slit along the optical axis (y) correspond to displacements of the diffracted beam focus position with respect to the Rowland circle (l f ). Note that for the jet in the middle of the entrance slit we have y = 0 and l f = 0. Also misalignments of the jet position perpendicular to the optical axis (x) can occur. Movements of the jet along the x-direction shift the spectrum on the detector (set tangential to the Rowland circle) by l s . The inset shows the full Rowland circle and positions of the entrance slit, the grating and the detector.
Response of the RIXS spectrometer to displacements of the liquid jet in the slitless mode of operation (measurement: markers; simulation: lines). Measurements were done at the O K-edge (main emission line at 525 eV) using grating G1 in 2nd order with a diameter of the jet of 20 μm. (a) Shift of the focus position (l f , blue) and resolution (red) for jet displacements along y-axis. The blue empty circles are measured focus positions and the blue line shows calculations based on Eq. (1). (b) Shift of the spectrum (l s , blue) and count rate (red) for jet displacements along x-axis. The blue empty circles are measured shifts of the spectrum and the blue line corresponds to a calculation based on the grating equation. Experimental count rates (red filled circles) are compared to the calculated grating illumination for grating G1 at an entrance slit width of 400 μm (20 μm jet, offset from the slit 10 mm).
Comparison of liquid methanol and ethanol RIXS spectra taken at an incident photon energy of 540 eV and measured (a) at the BESSYII U41-PGM beamline and (b) at the LCLS SXR beamline. For details on the experimental parameters see Table II.
Comparison of Fe(CO)5 RIXS spectra taken at an incident photon energy of 711.5 eV and measured (a) at the BESSYII UE56/1-PGM beamline and (b) at the LCLS SXR beamline. The BESSYII spectra in (a) were measured with horizontally and vertically polarized x-rays. The LCLS spectra we measured with horizontally polarized incident x-rays. For details on the experimental parameters see Table III.
Photon energy ranges reachable with the spectrometer. In the parentheses is the optimal resolution of the spectrometer at the given energy for 20 μm source width.
Relevant experimental parameters for the measurements of liquid methanol RIXS spectra at the LCLS SXR beamline and at the BESSYII U41-PGM beamline. RIXS spectra are displayed in Figure 6. The incident photon energy was 540 eV with a 3 eV bandwidth (FWHM).
Relevant experimental parameters for the experiment on the Fe(CO)5 solution at the LCLS SXR beamline and at the BESSYII UE56/1-PGM beamline. RIXS spectra are displayed in Figure 7. The photon energy was 711.5 eV with a 0.5 eV bandwidth at the LCLS and 0.3 eV bandwidth at the BESSYII (both FWHM).
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