Stimulated X-Ray Raman Scattering with Free-Electron Laser Sources
by
Nina Rohringer(CFEL)
→
Europe/Berlin
Room 3.11 (AER19)
Room 3.11
AER19
Description
X-ray free-electron lasers (XFELs) open the pathway to transfer non-linear spectroscopic techniques to the X-ray domain, to study the interplay of electronic and vibrational degrees of freedom by time-domain spectroscopy. A promising all X-ray pump probe technique is based on coherent stimulated electronic X-ray Raman scattering. We will present the first experimental demonstration of nearly saturated stimulated electronic X-ray Raman scattering using the LCLS XFEL in atomic neon. By tuning the relatively broad XFEL pulses to the core-excited Rydberg resonances in the pre K-edge region of neon, resonance scattered photons drive an avalanche of resonant inelastic X-ray scattering events, resulting in exponential amplification of the scattering signal with an enhancement of 6-7 orders of magnitude. Analysis of the line profile of the emitted radiation permits to demonstrate the cross over from amplified fluorescence to coherent resonance scattering. In combination with statistical covariance mapping, a high-resolution spectrum of the resonant inelastic X-ray scattering process can be obtained, opening the path to coherent stimulated X-ray Raman spectroscopy. An extension of these ideas to molecules and the results of a recent experiment in CO will be discussed. The high-gain regime, involving exponential amplification and strong-field effects will be contrasted to stimulated scattering at moderate X-ray intensities, which is more appropriate for spectroscopic studies. A critically assessment of the feasibility of more complex nonlinear X-ray spectroscopic techniques and requirements on the stability and pulse parameters of XFEL sources that could enable these new techniques, will be presented.
