Local-microfield enhancement of high-order harmonic generation and the associated electron dynamics

Abstract

The high-order harmonic generation (HHG) by local-microfield enhancement is investigated using the simple diatomic model H2+, which is initially prepared in coherent superposition of the ground state and the first excited state. The high-order harmonic spectroscopy is calculated by solving time-dependent schrödinger equation (TDSE) using the split-operator technique in a large internuclear distance. Numerically we use asymmetric-spatial mask functions, multi-trajectories contributions are revealed in the harmonic spectra, which contribute to different frequencies of harmonic spectroscopy. Also we numerically solve the Newton equation to get the classical analysis, the maximum return energies show great agreement with the cut-off energies of high-order harmonics from different trajectrories. Due to the tunneling ionization has a sensitive response to the instantaneous electric field, all the trajectories can be controlled by the carrier-envelop phase of intense few-cycle laser field. It is shown that electrons migrating directly from one nucleus to the neighboring one without typical tunneling ionization, contribute dominantly to the lower order harmonics, and the intensities are dramatically enhanced along with the enhancement of the local-microfield. The migration of electrons between nuclei in multi-nuclei model will mimic the dynamics of electrons in solids, which will shed light on HHG from solids especially with local impurity.