Delay in atomic photoionization

TL;DR

This paper investigates the timing differences in photoelectron emission from noble gases following attosecond XUV pulse absorption, highlighting the roles of electron scattering, correlations, and the streaking IR field in observed delays.

Contribution

The study combines numerical modeling and analysis to explain photoemission delays, emphasizing the influence of the streaking IR field over the XUV pulse alone.

Findings

Time delay between 2s and 2p emission in neon partially explained by electron interactions.

Numerical models account for less than half of the experimentally observed delay.

Streaking IR field likely contributes significantly to the measured delay.

Abstract

We analyze the time delay between emission of photoelectrons from the outer valence $ns$ and $np$ sub-shells in noble gas atoms following absorption of an attosecond XUV pulse. By solving the time dependent Schr\"odinger equation and carefully examining the time evolution of the photoelectron wave packet, we establish the apparent "time zero" when the photoelectron leaves the atom. Various processes such as elastic scattering of the photoelectron on the parent ion and many-electron correlation affect the quantum phase of the dipole transition matrix element, the energy dependence of which defines the emission timing. This qualitatively explains the time delay between photoemission from the $2s$ and $2p$ sub-shells of Ne as determined experimentally by attosecond streaking [{\em Science} {\bf 328}, 1658 (2010)]. However, with our extensive numerical modeling, we were only able to account for less than a half of the measured time delay of $21\pm5$ as. We argue that the XUV pulse alone cannot produce such a large time delay and it is the streaking IR field that is most likely responsible for this effect.