Probing complex electron dynamics in multieclecton atoms and one electron molecule ion in presence of ultra short laser pulse

Abstract

We performed an ab initio and accurate exploration of complex electron dynamics in multieclecton atoms and one electron molecule ion in presence of ultra short laser pulse. Particularly, an ab initio 3D precision calculation and analysis of high-order harmonic generation (HHG) of one electron molecule ion subject to intense ellipti- cally polarized laser pulses is presented along with the time-dependent generalized pseudospectral (TDGPS) method in two-center prolate spheroidal coordinates. The calculations are implemented for the ground and first excited electronic states of the interest molecule at the equilibrium internuclear separation as well as for the stretched molecule case. Weak even harmonics were detected in the HHG spectra of stretched molecules which were explained by the broken inversion symmetry due to dynamic lo- calization of the electron density near one of the nuclei. A clear theoretical explanation of the phenomenon is given within the Floquet formalism. The studies in presence of laser field, proceed by investigation on anomalous dependence of near-threshold har- monics on the ellipticity of the driving near-infrared laser field which originates from the near-resonant excitation of π-symmetry molecular orbitals. In presence of linear polarized field, we also studied the sub-cycle transient multiphoton ionization dynam- ics of atomic and molecular systems subject to intense near-infrared laser fields on the sub-femtosecond time scale. Multiple ionization bursts within a single optical cy- cle are pronounced in the time-dependent ionization rates not only for some diatomic molecular ions but also for hydrogen atoms. The analysis of the electron density in- forms that several distinct density portions can be formed and separated from the target within half cycle of the laser field. For the multi-electronic system, we present a comprehensive theoretical and com- putational study on harmonic generation (HG) of Li atoms in one- and two-photon Rabi-flopping regimes. Our all-electron approach is established on the time-dependent density-functional theory and includes polarization of the core and dynamic response of the electrons to the laser field. The results show that the population oscillations in the time domain with the Rabi frequency are reflected in the fine structure of the HG spectra and the finer structures of the harmonic peaks on the smaller frequency scale arise from the pulse-shape-related interference effects. These features are clearly seen in one-photon Rabi-flopping regime between some specific states however the pattern is more complex in the two-photon Rabi-flopping regime. Our findings can be used for developing coherent control methods for HG in the Rabi-flopping regime.