Non-sequential double ionization below laser-intensity threshold: Anticorrelation of electrons without excitation of parent ion

TL;DR

This paper proposes that simultaneous electron emission, rather than recollision-induced excitation, can explain the anticorrelation observed in non-sequential double ionization below laser-intensity threshold, supported by numerical and analytical models.

Contribution

It introduces an alternative mechanism for electron anticorrelation in double ionization below threshold, challenging the widely accepted recollision-induced excitation explanation.

Findings

Simultaneous electron emission explains anticorrelation without ion excitation.

Numerical solutions support the new mechanism.

Analytic models provide a closed-form understanding.

Abstract

Two-electron correlated spectra of non-sequential double ionization below laser-intensity threshold are known to exhibit back-to-back scattering of the electrons, viz., the anticorrelation of the electrons. Currently, the widely accepted interpretation of the anticorrelation is recollision-induced excitation of the ion plus subsequent field ionization of the second electron. We argue that another mechanism, namely simultaneous electron emission, when the time of return of the rescattered electron is equal to the time of liberation of the bounded electron (the ion has no time for excitation), can also explain the anticorrelation of the electrons in the deep below laser-intensity threshold regime. Our conclusion is based on the results of the numerical solution of the time-dependent Schr\"{o}dinger equation for a model system of two one-dimensional electrons as well as an adiabatic analytic model that allows for a closed-form solution.