Analytical model for attosecond time delays and Fano's propensity rules in the continuum

TL;DR

This paper introduces an analytical model that accurately predicts angular momentum-dependent phase shifts in attosecond photoionization delays and explains Fano's propensity rules in laser-assisted ionization.

Contribution

The study develops an analytical framework for two-photon transition amplitudes that captures angular quantum number effects and describes Fano's propensity rules.

Findings

Model reproduces phase dependence on angular momentum.

Explains Fano's propensity rules in laser-assisted photoionization.

Aligns with recent experimental observations.

Abstract

Extracting single photoionization time delays associated with atomic (or molecular) species from attosecond time scale two-photon experiments usually relies on the theoretical description of continuum-continuum transitions. The available models for those processes predict a universal phase contribution, independent of the angular quantum numbers of final states. However, a recent experimental-theoretical study [Fuchs, \emph{et al.} Optica 7, 154 (2020)] determined a sizable time delay dependence on the angular momentum of near-threshold photoelectrons. In this study, we present an analytical model for the two-photon two-color transition matrix amplitudes that reproduces the phase dependence on the angular quantum number of final states. Finally, we show that our analytical model can also describe the generalized Fano's propensity rules [Busto, \emph{et al.} Phys. Rev. Lett. 123, 133201 (2019)] for laser-assisted photoionization.