Energy Correlation in Above-Threshold Nonsequential Double Ionization at 800 nm

TL;DR

This study uses quantum calculations to analyze energy correlations in nonsequential double ionization of helium at 800 nm, revealing resonant processes and electron emission patterns influenced by Coulomb repulsion.

Contribution

It uncovers the role of resonant double ionization and Coulomb repulsion in electron energy correlations at sub-threshold intensities, advancing understanding of electron dynamics in strong fields.

Findings

Resonant double ionization involves electrons sharing photon energy.

Back-to-back electron emission is dominant due to Coulomb repulsion.

Two intensity-independent energy cutoffs are observed.

Abstract

We have investigated the energy correlation of the two electrons from nonsequential double ionization of helium atom in 800 nm laser fields at intensities below the recollision threshold by quantum calculations. The circular arcs structure of the correlated electron momentum spectra reveals a resonant double ionization process in which the two electrons transit from doubly excited states into continuum states by simultaneously absorbing and sharing excess energy in integer units of the photon energy. Coulomb repulsion between the two electrons in continuum states is responsible for the dominant back-to-back electron emission and two intensity-independent cutoffs in the two-electron energy spectra.