How intense laser light strips electrons from atoms

Overview

The problem

A very intense laser pulse can pull electrons out of an atom almost instantly. In heavier atoms, each electron's spin is linked to its motion (spin–orbit coupling), but how that link shapes the process in atoms with many electrons has been largely unexplored.

The approach

The method follows the electrons in real time using relativistic quantum mechanics, which includes the spin–orbit link from the start. An absorbing boundary removes electrons once they travel far from the atom, so the simulation can measure how quickly electrons are lost.

What it found

For krypton, the simulations reproduce how the rate of electron loss differs between the two spin–orbit states of its outer electrons (4p₁/₂ and 4p₃/₂). They also reveal a pathway, opened by spin–orbit coupling, that transfers electrons between those two states during the pulse, which is forbidden when spin–orbit coupling is ignored.

Abstract

Strong-field ionization exhibits rich ultrafast dynamics arising from intricate electron-field interactions. However, the role of spin-orbit coupling in the strong-field ionization of many-electron systems remains largely unexplored. Here, we develop a fully relativistic framework that combines a complex absorbing potential (CAP) with exact two-component (X2C) real-time time-dependent density functional theory. We apply this approach to investigate the real-time strong-field dynamics of atomic krypton with a variational treatment of spin-orbit coupling. The CAP-X2C method captures the spin-orbit-resolved ionization-rate trends of the Kr 4p shell. Moreover, we uncover a previously inaccessible coherent population transfer channel between the 4p₁/₂ and 4p₃/₂ states, opened by spin-orbit coupling, which lifts the nonrelativistic symmetry restriction that forbids their mixing. This work provides a practical framework for exploring strong-field dynamics in systems where spin-orbit coupling plays a significant role.

Spin–orbit-resolved strong-field ionization from real-time relativistic dynamics

Overview

The problem

The approach

What it found

Abstract