X-ray and extreme ultraviolet emission induced by variable pulse-width irradiation of Ar and Kr clusters and droplets

Measurements are presented of x-ray (>1.5 keV) and extreme ultraviolet (EUV, lambda = 2-44 nm) emission from argon and krypton supersonic gas jets at room (T = 300 K) and cryogenic (T = 173 K) temperatures irradiated with constant energy (50 mJ), variable width laser pulses ranging from 100 fs to 10 ns. Two regimes of jet operation are explored: cluster formation (radius < 100 nm) and droplet formation (radius > 1 mum). The results for both clusters and droplets can be understood in terms of two time scales: a short time scale for optimal resonant absorption at the critical density layer in the expanding plasma, and a longer time scale for the plasma to drop below critical density.