Two-photon double ionization of neon using an intense attosecond pulse train

TL;DR

This paper demonstrates two-photon double ionization of neon using an intense attosecond XUV pulse train, revealing the process is mainly sequential and enabling future ultrafast electron dynamics studies.

Contribution

First experimental demonstration of two-photon double ionization of neon with an attosecond pulse train in a regime allowing direct and sequential mechanisms.

Findings

Double ionization occurs mainly via a sequential process.

Tuning photon energy controls the double ionization signal.

Achieved high-intensity XUV pulse with ~1 μJ energy and 35 eV central energy.

Abstract

We present the first demonstration of two-photon double ionization of neon using an intense extreme ultraviolet (XUV) attosecond pulse train (APT) in a photon energy regime where both direct and sequential mechanisms are allowed. For an APT generated through high-order harmonic generation (HHG) in argon we achieve a total pulse energy close to 1 $\mu$J, a central energy of 35 eV and a total bandwidth of $\sim30$ eV. The APT is focused by broadband optics in a neon gas target to an intensity of $3\cdot10^{12} $W$\cdot$cm$^{-2}$. By tuning the photon energy across the threshold for the sequential process the double ionization signal can be turned on and off, indicating that the two-photon double ionization predominantly occurs through a sequential process. The demonstrated performance opens up possibilities for future XUV-XUV pump-probe experiments with attosecond temporal resolution in a photon energy range where it is possible to unravel the dynamics behind direct vs. sequential double ionization and the associated electron correlation effects.