Abstract
We describe the excitation and ionization of dense Ba vapour (1019 to 2021 m-3) by resonant (λ = 553.5 nm) laser radiation and discuss the processes responsible for the transfer of energy from the laser-excited atoms into ionization. Ionization was found to be density-dependent and this pointed to collision-dominated ionization mechanisms. It has been established that seed electrons were heated in superelastic collisions with laser-excited atoms, and that subsequent electron-impact excitation and ionization - as well as photoionization of high-lying levels - lead to the creation of more electrons. The observed transfer of the excitation energy to the electrons by superelastic collisions requires contributions not only from the laser-pumped resonance level, but also from the lower-lying metastable Ba levels. These were, in fact, found to be very efficiently populated via the resonance level.
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