Intensity dependence of strong field double ionization mechanisms: from field-assisted recollision ionization to recollision-assisted field ionization

TL;DR

This paper investigates molecular double ionization under intense laser fields, identifying distinct mechanisms across different intensity regimes and revealing a surprising anti-correlation in electron momenta near the over-the-barrier threshold.

Contribution

It introduces a detailed analysis of ionization mechanisms and momentum correlations using a three-dimensional quasiclassical model, bridging low and high intensity regimes.

Findings

Distinct ionization mechanisms identified in different intensity regimes.

Observation of anti-correlation in electron momenta near over-the-barrier intensity.

Correlation patterns serve as signatures for underlying ionization processes.

Abstract

Using a three-dimensional quasiclassical technique we explore molecular double ionization by a linearly polarized, infrared (800 nm) and ultrashort (6 fs) laser pulse. We first focus on intensities corresponding to the tunneling regime and identify the main ionization mechanisms in this regime. We devise a selection of observables, such as, the correlated momenta and the sum of the momenta parallel to the laser field as a function of the inter-electronic angle of escape where all the main mechanisms have distinct traces. Secondly, we address intensities above but close to the over-the-barrier intensity regime. We find a surprising anti-correlation of electron momenta similar to the experimental observations reported in Phys. Rev. Lett. \textbf{101}, 053001 (2008). There, however, the anti-correlation was observed in very low intensities corresponding to the multiphoton regime. We discuss the mechanism responsible for the anti-parallel two-electron escape.