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

Abstract

Extracting single photoionization time delays associated with atomic (or molecular) species from attosecond timescale 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 et al., Optica 7, 154 (2020)] determined a sizable time-delay dependence on the angular momentum of near-threshold photoelectrons. In this paper, 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.