Collision-enhanced plasmonic electron acceleration in small metal clusters.

Transient nanoplasmas in laser-excited metal clusters open the route to probing ultrafast collisional and collective laser-plasma processes in a wide and well-tunable range of densities and temperatures. The transition from a fully degenerate to a nearly classical plasma can occur within a few femtoseconds, accompanied by fundamental changes in the relaxation processes driven by electron-electron collisions (EECs). To investigate the resulting implications for laser-metal-cluster interactions, we developed an extended semiclassical Vlasov-Uehling-Uhlenbeck approach where the collision term resolves timedependent Pauli blocking and local screening effects for arbitrary levels of degeneracy. Our simulation results for resonant dual-pulse excitations of Na₅₅ reveal an unexpected synergy effect of EECs and collective laser-plasma processes, i.e. a strongly enhanced electron acceleration via plasmon-assisted rescattering in the presence of EECs. [ABSTRACT FROM AUTHOR]