The Heisenberg-RIXS instrument at the European XFEL

FELs (Free Electron Lasers) represent a groundbreaking innovation in the generation of high-brilliance, coherent, and tunable light, particularly in the X-ray regime. These X-rays possess unique properties compared to synchrotron radiation, including extraordinary brilliance, ultrashort pulses (lasting only a few tens of femtoseconds in standard operation), a specific time pattern, and highly coherent radiation both temporally and spatially. These features pave the way for a wide array of cutting-edge experiments, leveraging the ultrafast timescales provided by the FEL time structure and the remarkable power of X-rays. Notably, the high repetition rate of the European XFEL in Hamburg enables photon-hungry, time-resolved experiments, such as time-resolved RIXS (trRIXS), with exceptional energy and temporal resolution.

In this context, members of our team collaborated with researchers from the European XFEL, HZB, the University of Potsdam, DESY, and the University of Helsinki to develop a high-resolution RIXS spectrometer for the Spectroscopy and Coherent Scattering (SCS) instrument at the European XFEL.

When time becomes a decisive factor in a RIXS experiment, Heisenberg’s uncertainty principle defines the achievable limits of temporal and energy resolution, as shown in Figure 1. The Heisenberg-RIXS (hRIXS) instrument at the European XFEL is specifically designed to push these boundaries, achieving unprecedented performance in exploring the ultrafast dynamics of quantum materials and molecules. By optimizing the balance between temporal and energy constraints, the hRIXS spectrometer enables detailed investigations of electronic and vibrational excitations. With a combined resolving power (monochromator and hRIXS) above 10000 (Figure 2), limited by the beamline resolution, hRIXS stands as a unique tool to perform trRIXS studies with this performance.

The hRIXS design supports studies in the soft X-ray range (200–2000 eV) and provides flexible sample environments. It can be easily coupled with a diffraction chamber equipped with a six-axis diffractometer for solid sample studies and a second chamber for liquid jet systems used in chemical and molecular studies. The unique combination of the European XFEL’s exceptional repetition rate and the advanced design of hRIXS establishes it as a transformative tool for understanding ultrafast processes in condensed matter and photo-activated process in chemistry and molecules.

For further details, have a look at our recent publication Schlappa, Ghiringhelli et al., Journal of Synchrotron Radiation 2025;32(1):29-45.