Molecular Physics seminar

X-ray Raman scattering in linear and nonlinear regimes

by Victor Kimberg (KTH)

FA 31 ()

FA 31

X-ray Raman scattering is a well-established powerful tool for study of the electronic structure and nuclear dynamics in molecules, liquids and solids, surfaces. Traditional x-ray scattering spectroscopies are based on both radiative and nonradiative emission, such as non-resonant x-ray emission, resonant inelastic x-ray scattering (RIXS), Auger and resonant Auger spectroscopy. Recent invention of x-ray free-electron lasers (XFELs) providing ultrashort x-ray pulses with enormous photon flux (10-15 orders of magnitude higher than the conventional synchrotron radiation sources) allows to bring a qualitatively new aspect to x-ray spectroscopic techniques – x-ray nonlinearity. This very exciting development of the present day x-ray science is in a way similar to non-linear revolution in optical spectroscopy triggered by invention of the IR and optical lasers. In the present talk I would like to overview our resent theoretical results on spectroscopy of x-ray induced nuclear dynamics in both linear and nonlinear regimes. I will start with an introduction to the field of x-ray spectroscopy using several examples of our recent theoretical and experimental works in RIXS from gas-phase molecules. Our theoretical approach based on a combination of high-level ab initio calculations and quantum wave packet propagation formalism allows for an advance description of the nuclear dynamics beyond the Born-Oppenheimer and independent mode approximations [1]. Then I will focus on strong x-ray fields regime, discussing stimulated emission and lasing – the first x-ray non-linear effect already observed in atoms and predicted in molecules [2]. I will continue with more sophisticated all x-ray pump-probe schemes including stimulated RIXS spectroscopy with the coherent and stochastic light sources [3]. Finally, I will briefly present recent experimental attempts on stimulated RIXS in molecules [4] and address experimental feasibility for high-resolution nonlinear x-ray spectroscopy. [1] R. C. Couto, et al, Sci. Rep., 2016, 6, 20947; R. C. Couto, et al, Phys. Rev. A, 2016, 93, 32510. [2] V. Kimberg and N. Rohringer, Phys. Rev. Lett., 2013, 110, 43901; V. Kimberg, et al, J. Phys. Conf. Ser., 2014, 488, 12025; V. Kimberg, et al, J. Phys. B At. Mol. Opt. Phys., 2013, 46, 164017. [3] V. Kimberg and N. Rohringer, Struct. Dyn., 2016, 3, 34101. [4] V. Kimberg et al, Faraday Discussion, 2016, DOI: 10.1039/C6FD00103C; N. Rohringer, et al, in X-ray Lasers 2014. Proceedings of the 14th International Conference on X-Ray Lasers, eds. J. J. Rocca, C. Meloni and M. Marconi, 2016, vol. 169, p. 201.