Real-time tracking of two-electron dynamics in the ionization continuum of Xe

Abstract

Real-time tracking of atomic two-electron coherent dynamics is investigated through excitation of autoionizing wave packets in the ionization continuum of xenon. Extreme-ultraviolet high-order harmonics of ultrashort Ti:Sapphire laser pulses start the wave packets in energy ranges with a dense covering by two-valence-electron and single-inner-valence-electron excited-state resonances. The 15th harmonic covers resonances of type $5s5{p}^{6}nl$ with principle quantum number $n$ ranging from $n\ensuremath{\approx}14$ up to $n\ensuremath{\approx}21$ and one resonance of type $5{s}^{2}5{p}^{4}nl{n}^{\ensuremath{'}}{l}^{\ensuremath{'}}$ with fixed $n,\phantom{\rule{0.16em}{0ex}}{n}^{\ensuremath{'}}$ and orbital angular momenta $l,\phantom{\rule{0.16em}{0ex}}{l}^{\ensuremath{'}}$. In parallel the 17th harmonic starts a wave packet beyond the Xe $5s5{p}^{6}$ ionization threshold where exclusively resonances contribute with two-valence electrons being excited. The evolution in time of these wave packets is probed by inducing a continuum-continuum transition with the Ti:Sapphire laser pulses at variable delay times and detecting the photoelectrons after this two-photon transition. The dependence of the experimental data on the pump-probe delay time can be approximated by a two-photon transition probability derived on the basis of Fano's theory.