Resonant X-ray Emission Spectroscopy with a SASE Beam

Featured Application In the present work, RXES planes are reconstructed with high energy resolution from the experimental spectra of the X-ray radiation emitted from a sample and of incident X-ray pulses delivered by an XFEL operated in the raw SASE mode. The dependence of the reconstructed RXES planes' quality on the number of recorded XFEL shots is studied. Aqueous iron (III) oxide nanoparticles were irradiated with pure self-amplified spontaneous emission (SASE) X-ray free-electron laser (XFEL) pulses tuned to the energy around the Fe K-edge ionization threshold. For each XFEL shot, the incident X-ray pulse spectrum and Fe K beta emission spectrum were measured synchronously with dedicated spectrometers and processed through a reconstruction algorithm allowing for the determination of Fe K beta resonant X-ray emission spectroscopy (RXES) plane with high energy resolution. The influence of the number of X-ray shots employed in the experiment on the reconstructed data quality was evaluated, enabling the determination of thresholds for good data acquisition and experimental times essential for practical usage of scarce XFEL beam times.