Attosecond Photoemission Dynamics: Novel AB Initio Methods for Atomic and Molecular Ex-situ Spectrscopies

The University Of Central Florida Board Of Trustees, Orlando FL

Investigators

Abstract

At a fundamental level, atoms consists of negatively-charge particles, the electrons, flying around a massive positively-charged nucleus. Using ultrashort laser pulses, snapshots of electrons can be taken with attosecond time resolution (one attosecond is a billionth of a billionth of a second), which is the natural timescale of electronic motion. To control how atoms evolve in time, however, it is also essential to be able to predict their fast dynamics. This is a difficult task because electrons try to avoid each other in their motion around the nucleus. Furthermore, electrons occasionally do collide, causing the choreography of the dance to change. During the last three years, this research group has developed numerical tools that can predict how this complex dynamics unfolds under the influence of external light pulses. The present project will add to the theoretical toolbox the pieces necessary to describe three important aspects of electron dynamics; the interaction of their spin with their orbital motion, their interaction with circularly polarized light, and, in the case of molecular electrons, their interaction with two or more nuclear centers. These new tools will contribute to consolidate the U.S. presence in the ultrafast atomic and molecular international community, and to equip the students involved in this research with unique computational skills. Attosecond pulses have given access to the time-resolved study of electronic excitations in atoms and molecules above their ionization threshold. Such studies rely on ever more sophisticated theoretical models. Currently, it is possible to describe, within the electrostatic approximation, the ionization of systems as complex as neon and argon. Yet, the accurate treatment of atoms beyond the first period requires incorporation of their spin-orbit interaction. Thanks to constant experimental advances, the polarization of attosecond light pulses can now be changed at will, and it is possible to detect angularly resolved photoelectron spectra from oriented molecular targets. This project will include spin-orbit effects and the interaction with arbitrarily polarized pulses in the time-resolved description of atomic ionization, and it will extend existing molecular scattering codes to finite-pulse multi-photon ionization regimes. The inclusion of relativistic interactions will be essential to quantify the ionization delay due to the interplay between spin-orbit interaction and electron correlations. The study of ionization with arbitrarily polarized ultrashort pulses will open the way to non-axially symmetric photoemission. The new molecular-codes will be a more rigorous basis for attosecond interferometric spectroscopies. This project aims at solving persistent discrepancies in atomic attosecond experiments that are due to the non-negligible spin-orbit splitting in the valence and inner-valence shells of atoms as heavy as argon and krypton. It will explore new pump-prope schemes with circularly-polarized pulses, which hold the keys to the direct measurement of resonant retardation in photoemission and to the dichroism in the ionization of chiral systems. This project will also foster STEM excellence in Florida by promoting the participation of students from local high schools to the USA Physics Olympiads through off-campus training sessions. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.