Angular dependence of the Wigner time delay upon tunnel ionization of $H_{2}$

TL;DR

This paper presents experimental measurements of the Wigner time delay in strong-field tunnel ionization of H₂ molecules, revealing its dependence on electron emission direction and explaining it through electron travel path variations.

Contribution

It provides the first experimental data on Wigner time delay in molecular strong-field ionization and explains the observed dependence on emission direction.

Findings

Wigner time delay varies with electron emission direction.

Changes in delay are explained by electron travel path differences.

Spatial shifts of the electron's birth position influence the delay.

Abstract

More than 100 years after its discovery and its explanation in the energy domain, the duration of the photoelectric effect is still heavily studied. The emission time of a photoelectron can be quantified by the Wigner time delay. Experiments addressing this time delay for single-photon ionization became feasible during the last 10 years. A missing piece, which has not been studied, so far, is the Wigner time delay for strong-field ionization of molecules. Here we show experimental data on the Wigner time delay for tunnel ionization of $H_{2}$ molecules and demonstrate its dependence on the emission direction of the electron with respect to the molecular axis. We find, that the observed changes in the Wigner time delay can be quantitatively explained by elongated/shortened travel paths of the electrons that are due to spatial shifts of the electron's birth position after tunneling. This introduces an intuitive perspective towards the Wigner time delay in strong-field ionization.