Time-dependent multiconfiguration self-consistent-field study on resonantly enhanced high-order harmonic generation from transition-metal elements

摘要

We theoretically study high-harmonic generation (HHG) from transition-metal elements Mn and Mn+ using full-dimensional,all-electron,first-principles simulations.The HHG spectra calculated with the time-dependent complete-active-space self-consistent-field (TD-CASSCF) and occupation-restricted multiple-active-space (TDORMAS) methods exhibit a prominent peak at ~50 eV,successfully reproducing resonant enhancement observed in previous experiments [Opt.Express 20,25239 (2012)].Artificially freezing 3p orbitals in simulations results in its disappearance,which shows the essential role played by 3p electrons in the resonant harmonics (RH).Further transition-resolved analysis unambiguously identifies constructively interfering 3p-3d (m = 0,±1) giant resonance transitions as the origin of the RH,as also implied by its position in the spectra.Time-frequency analysis indicates that the recolliding electron combines with the parent ion to form the upper state of the transitions.In addition,this study shows that the TD-CASSCF and TD-ORMAS methods can be applied to open-shell atoms with many unpaired inner electrons.