Development of ion recoil energy distributions in the Coulomb explosion of argon clusters resolved by charge-state selective ion energy spectroscopy

TL;DR

This study investigates how ion recoil energies from Coulomb explosions of argon clusters depend on laser intensity, revealing complex charge distributions and challenging the assumption of homogeneous charge during explosion.

Contribution

It provides the first charge-state resolved measurements of ion recoil energies, showing that ion charge distributions are more complex than previously assumed.

Findings

High-energy tail of ion spectra develops a knee feature with increasing laser intensity.

Distinct gaps in low-energy yields indicate complex radial charge distributions.

Homogeneous charge sphere model is insufficient to describe the explosion dynamics.

Abstract

The laser intensity dependence of the recoil energies from the Coulomb explosion of small argon clusters has been investigated by resolving the contributions of the individual charge states to the ion recoil energy spectra. Between $10^{14}$ and $10^{15}$ W/cm$^2$ the high-energy tail of the ion energy spectra changes its shape and develops into the well-known knee feature, which results from the cluster size distribution, laser focal averaging, and ionization saturation. Resolving the contributions of the different charge states to the recoil energies, the experimental data reveal that the basic assumption of an exploding homogeneously charged sphere cannot be maintained in general. In fact, the energy spectra of the high-$q$ show distinct gaps in the yields at low kinetic energies, which hints at more complex radial ion charge distributions developing during the laser pulse impact.