Resonant inelastic x-ray scattering beyond the SASE resolution limit*

Resonant inelastic x-ray scattering (RIXS) is a widely used spectroscopic technique, providing access to the electronic structure and dynamics of atoms, molecules, and solids. However, RIXS requires a narrow bandwidth x-ray probe to achieve high spectral resolution. The challenges in delivering an energetic monochromated beam from an x-ray free electron laser (XFEL) thus limit its use in few-shot experiments, including for the study of high energy density systems.

Here we demonstrate that by correlating the measurements of the SASE x-ray spectrum and the RIXS signal, combined with dynamic kernel deconvolution using differentiable programming with a neural surrogate, we can achieve electronic structure resolutions substantially higher than that normally afforded by the bandwidth of the incoming x-ray beam. We further show how this technique allows us to discriminate between the valence structures of Fe and Fe₂O₃, and provides access to temperature measurements and M-shell binding energies estimates in warm-dense Fe compounds.