Retrieving intracycle interference in angular-resolved laser-assisted photoemission from argon

TL;DR

This study combines experimental and theoretical methods to observe intracycle interference effects in angle-resolved laser-assisted photoemission from argon, revealing subtle interference patterns by subtracting averaged spectra.

Contribution

It demonstrates a novel approach to recover intracycle interference patterns in photoelectron spectra through differential averaging of experimental and theoretical data.

Findings

Intracycle interference patterns are observable after subtracting averaged spectra.

Theoretical calculations match experimental observations when accounting for focal volume averaging.

Intracycle interference modulates the sideband structures in photoemission spectra.

Abstract

We report on a combined experimental and theoretical study of XUV ionization of atomic argon in the presence of a near-infrared laser field. The resulting energy- and angle- resolved photoemission spectra have been described in the literature as interferences among different photoionization trajectories. Electron trajectories stemming from different optical laser cycles give rise to \textit{intercycle} interference energy and result in new peaks known as sidebands. These sidebands are modulated by a coarse grained (gross) structure coming from the \textit{intracycle} interference of the electron trajectories born during the same optical cycle. We calculate the photoelectron emission by solving the time-dependent Schr\"{o}dinger equation \textit{ab initio} and within the continuum-distorted wave strong field approximation. In order to compare with the experimental data we average the calculated energy-angle probability distributions over the experimental focal volume. This averaging procedure washes out the intracycle interference pattern, which we experimentally and theoretically (numerically) recover by subtracting two averaged distributions for slightly different near-infrared laser field intensities.