Abstract
The modification of ion production efficiency via resonant laser-driven ionisation in the presence of high buffer gas atmospheres has been experimentally investigated in a barium vapour. The populations of several energy levels of neutral and singly ionised Ba were measured as a function of both helium and argon pressures by the time-resolved hook technique. The behaviours of He and Ar are quite distinct. The percentage of ionisation decreased monotonically from nearly 100% to less than 10% as the helium pressure was increased from 0.01 to 1 atm, while no quenching was observed in 1 atm of Ar. These observations are consistent with a quenching mechanism based in part on cooling of the 'hot' electrons through momentum-changing elastic collisions with the He atoms.
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