Strong-field ionization and Coulomb explosion of small neodymium and europium oxide clusters

A femtosecond visible ring dye laser centered at 624 nm is used to probe the ionization dynamics of small neodymium and europium oxide clusters. Semi-classical atomic tunneling theory using sequential ionization potential values is compared to experimental ion signal and the gaps between the saturation intensities of each charge state are quantified. Differences in saturation intensities for the onset of ion signal between atomic charge states were found to increase as the metal–oxygen bond strength of the cluster increases. Neodymium showed larger enhancements in ionization whereas larger gaps in ion signal between europium charge states indicate more sequential-like ionization.