Ion Recoil Energy Signatures of Geometric Shells from the Coulomb Explosion of Size-Selected Silver Clusters

The strong-field dynamics of laser-produced nanoplasmas generated from free and size-selected silver clusters, Ag_N^-, are analyzed by charge-state-resolving ion recoil energy spectrometry. Targeted excitation of the plasmon resonance increases the plasma electron temperature, which has an effect on ion screening, electron-ion recombination, and correlated decay. By minimizing these complex contributions to the ion expansion through plasmonic energy uptake, pronounced peaks show up in the ion recoil energy spectra, which can be assigned to the emission of ions from different geometrical shells reflecting the initial cluster structure. The feature becomes particularly pronounced upon reaching the icosahedral shell closing at a cluster size of N = 55. A signature of geometrical shells is also observed for Ag₁₄₇^-, which underpins the scalability of the approach via plasmon-assisted control of the nanoplasma dynamics.