Shot noise limited soft x-ray absorption spectroscopy in solution at a SASE-FEL using a transmission grating beam splitter

Robin Y. Engel, Maria Ekimova, Piter S. Miedema, Carlo Kleine, Jan Ludwig, Miguel Ochmann, Benjamin Grimm-Lebsanft, Rory Ma, Melissa Teubner, Siarhei Dziarzhytski, Günter Brenner, Marie Kristin Czwalinna, Benedikt Rösner, Tae Kyu Kim, Christian David, Sonja Herres-Pawlis, Michael Rübhausen, Erik T.J. Nibbering, Nils Huse, Martin Beye

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3 Citations (Scopus)


X-ray absorption near-edge structure (XANES) spectroscopy provides element specificity and is a powerful experimental method to probe local unoccupied electronic structures. In the soft x-ray regime, it is especially well suited for the study of 3d-metals and light elements such as nitrogen. Recent developments in vacuum-compatible liquid flat jets have facilitated soft x-ray transmission spectroscopy on molecules in solution, providing information on valence charge distributions of heteroatoms and metal centers. Here, we demonstrate XANES spectroscopy of molecules in solution at the nitrogen K-edge, performed at FLASH, the Free-Electron Laser (FEL) in Hamburg. A split-beam referencing scheme optimally characterizes the strong shot-to-shot fluctuations intrinsic to the process of self-amplified spontaneous emission on which most FELs are based. Due to this normalization, a sensitivity of 1% relative transmission change is achieved, limited by fundamental photon shot noise. The effective FEL bandwidth is increased by streaking the electron energy over the FEL pulse train to measure a wider spectral window without changing FEL parameters. We propose modifications to the experimental setup with the potential of improving the instrument sensitivity by two orders of magnitude, thereby exploiting the high peak fluence of FELs to enable unprecedented sensitivity for femtosecond XANES spectroscopy on liquids in the soft x-ray spectral region.

Original languageEnglish
Article number014303
JournalStructural Dynamics
Issue number1
Publication statusPublished - 2021 Jan 1

Bibliographical note

Funding Information:
We acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. The presented measurements were carried out at the PG2 monochromator beamline of FLASH. The authors are very thankful to the involved groups at DESY for the active support. We thank Simon Schreck and Philippe Wernet for recording the ACN reference spectrum. R.Y.E., P.S.M., and M.B. were funded by the Helmholtz Association through Grant No. VH-NG-1105. M.O. and N.H. gratefully acknowledge funding from the German Science Foundation (DFG) within the collaborative research center SFB 925 “Light induced dynamics and control of correlated quantum systems” (project A4). M.E., C.K., J.L., and E.T.J.N. acknowledge support from the German Science Foundation (Project No. DFG-NI 492/11–1) and the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (ERC Grant Agreement No. 788704; E.T.J.N.).

Publisher Copyright:
© 2021 Author(s).

All Science Journal Classification (ASJC) codes

  • Radiation
  • Instrumentation
  • Condensed Matter Physics
  • Spectroscopy


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