Effect of electron correlations on attosecond photoionization delays in the vicinity of the Cooper minima of argon

TL;DR

This study measures attosecond photoionization delays in argon near the Cooper-like minimum at 42 eV, revealing significant electron correlation effects that challenge single-particle models and require further theoretical refinement.

Contribution

First experimental measurement of photoionization delays near the Cooper-like minimum in argon, highlighting electron correlation effects with unprecedented temporal resolution.

Findings

Photoionization delays up to 430 as observed

Delays are influenced by electron correlation effects

Results partially agree with existing theories

Abstract

Attosecond photoionization delays have mostly been interpreted within the single-particle approximation of multi-electron systems. The strong electron correlation between the photoionization channels associated with the 3p and 3s orbitals of argon presents an interesting arena where this single-particle approximation breaks down. Around photon energies of 42~eV, the 3s photoionization channel of argon experiences a ``Cooper-like" minimum, which is exclusively the result of inter-electronic correlations with the 3p shell. Photoionization delays around this ``Cooper-like" minimum have been predicted theoretically, but experimental verification has remained a challenge since the associated photoionization cross section is inherently very low. Here, we report the measurement of photoionization delays around the Cooper-like minimum that were acquired with the 100~kHz High-Repetition 1 laser system at the ELI-ALPS facility. We report relative photoionization delays reaching up to unprecedented values of 430 +/- 20~as, as a result of electron correlation. Our experimental results are in partial agreement with state-of-the-art theoretical results, but also demonstrate the need for additional theoretical developments.