Atomic population redistribution in a dense Ga vapour proceeding via energypooling ionization induced by resonant laser-assisted collisions

Abstract

In this paper we report on the atomic population redistribution originatingfrom the ionization that takes place in a dense Ga vapour kept in quartzcells and resonantly excited by laser radiation, in the collisions betweentwo excited atoms. This ionization process is known as energy-poolingionization (EPI). The electron/ion recombination that takes place in the lowdensity plasma produced gives rise to population in the atomic Rydberglevels and from the latter via cascade transitions to lower lying ones. Wehave monitored the fluorescences relative to the radiative emissions fromsuch levels, namely those corresponding to the nP → 5S1/2 series, with 9 ≤ n ≤ 26, and the 4D → 4P1/2,3/2transitions. Their characteristics testify to their origin as being due to the EPIprocess. Further confirmation is obtained by performing a time-resolved analysis ofsuch fluorescences, whose appearance and time evolution is strongly influenced by thedynamics of the process. The effect of the introduction of a few Torr of buffer gasinside the quartz cell, resulting in the quenching of all the fluorescences for n ≥ 12, isalso discussed.