Intrinsic resonant photoionization time delay of hydrogen atoms probed with attosecond beating of asymmetrical photon transitions

Abstract

We investigate the benchmark photoionization of hydrogen atoms triggered by the third harmonic at vacuum ultraviolet laser pulses (at 202 nm) and probe the time delay via resonant quantum states with the weak fundamental laser pulses (at 606 nm). As a result, two different sidebands will emerge below the first above threshold ionization peak. We show that these two sidebands can be established through resonance with the $3d$ and $2p$ states of hydrogen atoms at 202 nm, respectively. Using this scheme, we can extract the angularly dependent time delay of electrons liberated from the $3d$ state with respect to those released from the $2p$ state by comparing the phase differences between two sidebands. Using the attosecond beating scheme of asymmetrical photon transition, we obtain the intrinsic time delay between the $3d$ and $2p$ excited electronic states in the few-photon ionization regime of H atoms, which is \ensuremath{\sim}103 as. This asymmetric attosecond beating metrology provides insight into electron dynamics of the multiphoton resonant ionization via multi-intermediate states.