General properties of the RABBITT at parity mixing conditions

TL;DR

This paper investigates the symmetry properties of a novel two-sideband RABBITT scheme enabled by free-electron lasers, analyzing how parity mixing affects photoelectron angular distributions and pulse characterization.

Contribution

It introduces a comprehensive analysis of the 2-SB RABBITT scheme's symmetry properties and differences from traditional methods, with implications for pulse measurement.

Findings

Identified key symmetry differences between 2-SB RABBITT and traditional schemes.

Demonstrated the impact of polarization geometry on angular distribution symmetry.

Showed potential for pulse shape reconstruction from angle-resolved data.

Abstract

Parity mixing in photoionization, i.e. when emitted electrons have different parities but the same energy, causes interference observable only in angle-resolved measurements. The interference typically manifests as a symmetry violation in the photoelectron angular distributions. The traditional, based on HHG, RABBITT scheme with high-order harmonics separated by twice the seed field energy, precludes parity mixing. On the contrary, a free-electron laser provides a possibility to generate even harmonics. Using triple the fundamental frequency as a seed, one obtains a comb of alternating even and odd harmonics, separated by three times the initial frequency [Nature 578, 386-391 (2020)] (2-SB RABBITT). In this setup, there are two sidebands between the main photoelectron lines, versus one in the traditional scheme. In the paper, we examine the general properties of a two-sideband scheme and analyze the symmetry breakdown of photoelectron angular distributions for various polarization geometries of the incident pulse. We found a crucial difference in symmetries between 2-SB RABBITT and other photoionization schemes with parity mixing. Illustrative calculations are carried out for neon with pulse parameters typical for modern facilities. The possibility to reconstruct the temporal profile of the pulse from the angle-resolved measurements is discussed.