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6Complex Systems of Charged Particles and their Interactions with Electromagnetic Radiation 2019
ELEMENTARY PROCESSES IN ATOMS AND IONS IN THE FIELD OF X-
RAY FREE ELECTRON LASERS
A.N. Grum-Grzhimailo1, E.V. Gryzlova1, M.M. Popova2, E.I. Staroselskaya2,
1Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Moscow, Russia,
e-mail: grum@sinp.msu.ru 2 Faculty of Physics, Lomonosov Moscow State University, Moscow 119991, Russia
With the advent of X-ray free-electron lasers (XFELs) the researchers obtained sources with unique combination of characteristics: adjustable wavelengths in the XUV and X-ray ranges, high intensity, femtosecond (soon attosecond) pulse duration, coherence, and variable polarization. Opening opportunities give rise to studies of phenomena that were previously unavailable for observation or accessible only in the optical range. This already has led to the birth of new branches of the physics of the interaction of electromagnetic radiation with matter. One of the examples is nonlinear processes in the X-ray domain. We will concentrate on two such processes: sequential two-photon double ionization (S2DI) and ionization by a combination of fundamental frequency and its second harmonic (process w+2w).
The S2DI was the first elementary process registered at XFEL. It gave birth to photoelectron spectroscopy of positively charged ions. This field is rapidly developing [1]. Recently the first 'complete' experiment on photoionization of positively charged ion was performed [2] and the non-dipole effects detected [3].
The process w+2w, well known and realized near to 30 years ago in the optical domain, became possible in the XUV with the advent of the first seeded XFEL FERMI with large time of coherence. In the first experiment of this type, the coherent control was demonstrated of the photoelectron angular distribution by changing relative phase of the harmonics of the XFEL [4].
A brief overview of experimental and theoretical results for the above processes will be given.
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Reconstructed density of outgoing electrons
Fig. 1. Reconstruction of the photoelectron density in 'complete' experiment on photoionization of Ne+.
E.V.G. and E.I.S. acknowledge support of the Foundation for the Advancement of Theoretical Physics and Mathematics BASIS.
References
[1] A.N. Grum-Grzhimailo et al. 2016 J. Mod. Opt. 60, 334.
[2] P A. Carpeggiani et al. 2019 Nat. Physics 15, 170.
[3] M. Ilchen et al. 2018 Nat. Communications 9, 4659.
[4] K.C. Prince et al. 2016 Nat. Photonics 10, 176.
