Efficiency of dopant-induced ignition of helium nanoplasmas

Abstract

Helium nanodroplets irradiated by intense near-infrared laser pulses ignite and form highly ionized nanoplasmas even at laser intensities where helium is not directly ionized by the optical field, provided the droplets contain a few dopant atoms. We present a combined theoretical and experimental study of the He nanoplasma ignition dynamics for various dopant species. We find that the efficiency of dopants to ignite a nanoplasma in helium droplets strongly varies and mostly depends on (i) the number of free electrons each dopant donates upon ionization, (ii) the pick-up process, and (iii) the hitherto unexplored effect of the dopant location in or on the droplet.