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

TL;DR

This study investigates how laser-assisted collision influences the nonsequential double ionization of helium in intense, few-cycle laser pulses, revealing distinct momentum distribution patterns across different laser intensities.

Contribution

It introduces the concept of laser-assisted collision ionization as a dominant mechanism in high-intensity regimes of NSDI, expanding understanding of ionization processes in strong laser fields.

Findings

Momentum distribution transitions from single to double peaks with increasing laser intensity.

Laser-assisted collision ionization dominates at high intensities, leading to single-peak momentum distribution.

Different NSDI mechanisms are identified across three laser intensity regimes.

Abstract

Nonsequential double ionization (NSDI) of helium in an intense few-cycle laser pulse is investigated by applying the three-dimensional semi-classical re-scattering method. It is found that the momentum distribution of He$^{2+}$ 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 He$^{2+}$ 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.