Multi-sideband interference structures by high-order photon-induced continuum-continuum transitions in helium

TL;DR

This study investigates interference effects in helium using a modified three-sideband RABBITT technique, combining experimental measurements and theoretical calculations to understand continuum-continuum transitions and their phase behaviors.

Contribution

It introduces a three-sideband RABBITT method for helium, providing new insights into continuum-continuum interference effects and phase analysis in a simplified atomic system.

Findings

Qualitative agreement between experiment and theory

Observed significant quantitative discrepancies

Insights into phase differences in continuum transitions

Abstract

Following up on a previous paper on two-color photoionization of Ar(3p) [Bharti et al., Phys. Rev. A 103 (2021) 022834], we present measurements and calculations for a modified three-sideband (3-SB) version of the "reconstruction of attosecond beating by interference of two-photon transitions" (RABBITT) configuration applied to He(1s). The 3-SB RABBITT approach allows us to explore interference effects between pathways involving different orders of transitions within the continuum. The relative differences in the retrieved oscillation phases of the three sidebands provide insights into the continuum-continuum transitions. The ground state of helium has zero orbital angular momentum, which simplifies the analysis of oscillation phases and their angle-dependence within the three sidebands. We find qualitative agreement between our experimental results and the theoretical predictions for many cases but also observe some significant quantitative discrepancies.