High Energy Ion Explosion of Atomic Clusters: Transition from Molecular to Plasma Behavior

We have studied the high-intensity femtosecond photoionization of inertially confined noble-gas clusters. The explosion of the resulting highly ionized, high-temperature microplasma ejects ions with substantial kinetic energy. We have observed Xe ions with kinetic energy up to 1 MeV and charge states as high as ${40}^{+}$. This ion energy is over three orders of magnitude higher than has previously been observed in the Coulomb explosion of molecules or clusters of any kind and indicates that there is a fundamental shift in the nature of intense laser-matter interactions between molecules and large clusters.