Laser-assisted collision effect on non-sequential double ionization of helium in a few-cycle laser pulse

Abstract

Non-sequential double ionization (NSDI) of helium in an intense few-cycle laser pulse is investigated by applying the three-dimensional semi-classical rescattering method. It is found that the momentum distribution of He2+ shows a single–double–single peak structure as the pulse intensity increases. According to the different mechanisms dominating the NSDI process, the laser intensity can be classified into three regimes where the momentum distribution of He2+ exhibits different characteristics. In the relatively high intensity regime, an NSDI mechanism named the ‘laser-assisted collision ionization’ is found to be dominating the NSDI process and causing the single-peak structure. This result can shed light on the study of non-sequential ionization of a highly charged ion in a relatively intense laser pulse.