Fano-line-shape metamorphosis in resonant two-photon ionization

In the Fano resonant ionization process, a decaying autoionizing state (AIS) is imbedded in the continuum resulting in a characteristic asymmetric photoelectron line shape. When the ionizing XUV pump is aided by a weak IR probe, the resonant path of the Fano process is transferred to the adjacent sidebands. As the XUV-IR delay grows, this resonant part of the sideband becomes decoupled from the embedding continuum. In result, the sideband line shape becomes symmetric and its magnitude decreases exponentially with the timing constant of the AIS decay. In the present work we simulate this process to extract the lifetime of several AISs in the He atom and the Li+ ion with sufficient numerical accuracy. The proposed method can be realized experimentally in diverse quantum systems ranging from nuclei to nanofabricated solids.