Laser-induced nonsequential double ionization at and above the recollision-excitation-tunneling threshold

TL;DR

This paper analyzes the RESI mechanism in laser-induced nonsequential double ionization, revealing how electron momentum distributions encode information about atomic states and identifying a threshold intensity for the process.

Contribution

It introduces a detailed analysis of the RESI mechanism, including the threshold intensity and the symmetry of electron momentum distributions, with computations for helium and argon.

Findings

Momentum distributions reveal information about bound states and electron interactions.

A specific intensity threshold for RESI is identified.

Distributions are symmetric across all quadrants, not just two.

Abstract

We perform a detailed analysis of the recollision-excitation-tunneling (RESI) mechanism in laser-induced nonsequential double ionization (NSDI), in which the first electron, upon return, promotes a second electron to an excited state, from which it subsequently tunnels, based on the strong-field approximation. We show that the shapes of the electron momentum distributions carry information about the bound-state with which the first electron collides, the bound state to which the second electron is excited, and the type of electron-electron interaction. Furthermore, one may define a driving-field intensity threshold for the RESI physical mechanism. At the threshold, the kinetic energy of the first electron, upon return, is just sufficient to excite the second electron. We compute the distributions for helium and argon in the threshold and above-threshold intensity regime. In the latter case, we relate our findings to existing experiments. The electron-momentum distributions encountered are symmetric with respect to all quadrants of the plane spanned by the momentum components parallel to the laser-field polarization, instead of concentrating on only the second and fourth quadrants.