Time Delays from One-Photon Transitions in the Continuum

Photoemission time delays reveal information about the potential landscape an electron probes upon ionization. Here, we quantify the dependence of the time delay on the angular momentum of the electrons liberated by ionization of the helium atom, analyzing the energy and angularly-resolved electron distribution within a two-color attosecond pump-probe scheme. These measurements allow us to disentangle the relative phase of all quantum pathways contributing to the photoelectron signal. In particular, we retrieve the dependence on the angular momentum of the Bremsstrahlung delay, which is an essential contribution to the ionization delay observed in all attosecond pump-probe measurements. We observe a continuum-continuum transition delay between outgoing s- and d-electrons as large as 12 as close to the ionization threshold. Both single-active-electron and full \emph{ab initio} simulations confirm this observation for helium and hydrogen, suggesting that these delays are universal.