Tracing transient charges in expanding clusters

Abstract

We study transient charges formed in methane clusters following ionization by intense near-infrared laser pulses. Cluster ionization by 400 fs ($I=1\times 10^{14}$ W/cm${}^2$) pulses is highly efficient, resulting in the observation of a dominant C${}^{3+}$ ion contribution. The C${}^{4+}$ ion yield is very small, but is strongly enhanced by applying a time-delayed weak near-infrared pulse. We conclude that most of the valence electrons are removed from their atoms during the laser-cluster interaction, and that electrons from the nanoplasma recombine with ions and populate Rydberg states when the cluster expands, leading to a \textit{decrease} of the average charge state of individual ions. Furthermore, we find clear bound-state signatures in the electron kinetic energy spectrum, which we attribute to Auger decay taking place in expanding clusters. Such nonradiative processes lead to an \textit{increase} of the final average ion charge state that is measured in experiments. Our results suggest that it is crucial to include both recombination and nonradiative decay processes for the understanding of recorded ion charge spectra.

arXiv comment5 pages, 4 figures

References in corpus (6)

• Laser-driven nonlinear cluster dynamics
• Storage ring measurement of the C IV recombination rate coefficient
• Rare-gas clusters in intense VUV, XUV and soft x-ray pulses: Signatures of the transition from nanoplasma-driven cluster expansion to Coulomb explosion in ion and electron spectra
• Steplike intensity threshold behavior of extreme ionization in laser-driven Xe clusters
• Ionization avalanching in clusters ignited by extreme-ultraviolet driven seed electrons
• Proton ejection from molecular hydride clusters exposed to strong X-ray pulses

Cited by in corpus (2)

• Time-resolved formation of excited atomic and molecular states in XUV-induced nanoplasmas in ammonia clusters
• Evolution and ion kinetics of a XUV-induced nanoplasma in ammonia clusters