High frame rate RIXS spectroscopy using a JUNGFRAU detector with an iLGAD sensor

Resonant inelastic X-ray scattering (RIXS) is a powerful photon-in, photon-out spectroscopy technique for probing electronic, magnetic, and lattice excitations in matter. Time-resolved RIXS extends this capability through a stroboscopic optical pump-probe scheme to characterize the time evolution of the photoexcitation and subsequent relaxation dynamics of a sample. This technique is, however, extremely photon-hungry, requiring high-repetition-rate and intense X-ray facilities. The Heisenberg RIXS (hRIXS) spectrometer at the Spectroscopy and Coherent Scattering (SCS) instrument of the European X-ray Free-Electron Laser (EuXFEL) is designed to exploit high-repetition-rates, while maintaining optimal time and energy resolution. In this work, we demonstrate the successful deployment of a JUNGFRAU detector equipped with an inverse Low Gain Avalanche Diode (iLGAD) sensor for time-resolved RIXS studies in the soft X-ray range, using the hRIXS spectrometer. A spatial resolution of $19.71 \pm 0.7~\mu\mathrm{m}$ and a resolving power exceeding 10,000 were achieved at an unprecedented frame rate of 47 kHz. Intra-train resolved data measured with a high FEL peak fluence of $1.8~\mathrm{mJ/cm^{2}}$ for a 928.5 eV ph photon energy and 1.1 MHz repetition rate from cupric oxide (CuO) revealed a decrease in the emitted signal by ~10% over a time interval of $340~\mu\mathrm{s}$, indicating FEL-induced effects that require monitoring when conducting high-repetition-rate experiments. These results establish the JUNGFRAU-iLGAD as a promising detector to harvest the full potential of the hRIXS spectrometer, and validate its suitability for soft X-ray applications.