Theoretical seminar. Volotka

04.03.2020
12:00
Begin
04.03.2020
12:00
Place

9 Lomonosov st.

Room 2530

En

Andrey V. Volotka (ITMO University, ITMO fellowship winner)

 'Quantumelectrodynamics with atoms and ions'

Abstract: Recent theoretical progress in ab initio quantum electrodynamical (QED) description of atoms and ions is reviewed. The first part is devoted to the spectroscopical properties, such as binding and transition energies, hyperfine structure, and g factor. Basics of the bound-state QED perturbation theory, Feynman diagrams, and renormalization procedure is given. Particular attention is paid to comparison of the theoretical predictions with recent experimental results for the transition energies in F-like ions, the hyperfine splittings in H- and Li-like bismuth ions, and g factors of Li-like silicon and B-like argon ions. In the second part, I focus on the nonlinear electron dynamics, namely on the two-photon processes, such as atomic photoionization, two-photon decay, Rayleigh scattering, and positron annihilation. Special attention is given to the two-photon direct ionization of the core-electrons in neutral atoms. This process attracts a lot of attention due to the recent development of free-electron lasers, intense-light sources operating in the ultraviolet and x-ray energy domains. However, its precise comparison with the experiments is hampered by the uncertainty in a resulting cross section, which can reach up to an order of magnitude. Recently, we predict the existence of a so-called nonlinear Cooper minimum, i.e. photon energy at which the dominant ionization channel vanishes. It appears that the Cooper minimum can be used as a precise tool for understanding nonsequential two-photon ionization.