Observation of Above-Threshold Dissociation of Na$_2^+$ in Intense Laser Fields

TL;DR

This paper reports the first observation of above-threshold dissociation in Na$_2^+$ molecules under intense laser fields, revealing new dissociation channels driven by continuum-continuum transitions.

Contribution

It demonstrates above-threshold dissociation in a multielectron molecule and identifies the dominant process at specific laser intensities, advancing understanding of molecular dynamics in strong fields.

Findings

Three dissociation channels observed with distinct energy patterns

Above-threshold dissociation dominates over Coulomb explosion at certain intensities

Continuum-continuum transitions are responsible for the observed dissociation

Abstract

We report the observation of above-threshold dissociation of a multielectron molecular system, Na$_2^+$. The process is due to continuum-continuum transitions in a field-dressed molecular continuum. Three well resolved fragmentation channels with different kinetic energy release patterns have been detected, of which, two are associated with ordinary photodissociation via light-induced potentials into Na(3s) + Na$^+$ and Na(3p) + Na$^+$, and one with continuum-continuum transitions and above-threshold dissociation into Na(3p) + Na$^+$. We show that when we dress this molecule with a field whose intensity is ~3 x 10$^{12}$ W/cm$^2$, above-threshold dissociation prevails over other processes, such as field-ionization followed by Coulomb explosion.