19 September 2022 in the frame of Science@FELs 2022
Linda Young, Argonne National Laboratory/UChicago
Stimulated X-ray Raman Spectroscopy with SASE pulses
X-ray free electron lasers have been proposed for the past two decades as a site-specific local probe of ultrafast electronic excitations. The use of nonlinear two-photon x-ray Raman techniques in this quest holds the promise of beating the core-hole lifetime that limits standard x-ray absorption and emission methods. In analogy with optical coherent Raman scatering techniques that probe ultrafast vibrational processes, x-ray nonlinear Raman scatering can probe ultrafast electronic processes. We build from two pillars – the use of propagation techniques in dense media to amplify spontaneous Raman signals by ~108 and the narrowband spectral spikes inherent in SASE pulses – to demonstrate high-resolution stimulated x-ray Raman spectroscopy (bandwidths ~0.3 eV) using broadband SASE pulses (~7 eV bandwidth). The ability to use broadband SASE pulses to achieve high-resolution, ultrafast x-ray Raman spectral snapshots allows one to rapidly acquire data in parallel over the SASE bandwidth, i.e. without scanning monochromatized x-ray pulses in conjunction with high-resolution x-ray emission spectrometers, and to extract correlated electronic excitations arising from different elements of a SASE pulse.
Work supported by U.S. Department of Energy, Office of Science, Basic Energy Science, Chemical Sciences, Geosciences and Biosciences Division under contract number DE-AC02-06CH11357. Experimental data acquired at the Small Quantum Systems end-station at the European XFEL under proposal number 2748.