Direct versus Delayed pathways in Strong-Field Non-Sequential Double Ionization

TL;DR

This study compares quantum and classical models of helium double ionization under laser fields, identifying two main pathways—direct and delayed—with their relative significance depending on laser intensity and electron energy.

Contribution

It introduces a detailed analysis of direct and delayed ionization pathways, highlighting their energy dependence and dominance at different laser intensities in strong-field double ionization.

Findings

Classical trajectories reveal two distinct ionization pathways.

The direct pathway dominates at lower energies and intensities.

The delayed pathway remains dominant at higher energies across all intensities.

Abstract

We report full-dimensionality quantum and classical calculations for double ionization of laser-driven helium at 390 nm. Good qualitative agreement is observed. We show that the classical double ionization trajectories can be divided into two distinct pathways: direct and delayed. The direct pathway, with an almost simultaneous ejection of both electrons, emerges from small laser intensities. With increasing intensity its relative importance, compared to the delayed ionization pathway, increases until it becomes the predominant pathway for total electron escape energy below around 5.25 $U_{p}$. However the delayed pathway is the predominant one for double ionization above a certain cut-off energy at all laser intensities.