Ion dynamics of a laser produced aluminium plasma at different ambient pressures

Abstract

Plasma is generated by pulsed laser ablation of an Aluminium target using 1064 nm, 7 ns Nd:YAG laser pulses. The spatial and temporal evolution of the whole plasma plume, as well as that of the ionic (Al²⁺) component present in the plume, are investigated using spectrally resolved time-gated imaging. The influence of ambient gas pressure on the expansion dynamics of Al²⁺ is studied in particular. In vacuum (10⁻⁵ Torr, 10⁻² Torr) the whole plume expands adiabatically and diffuses into the ambient. For higher pressures in the range of 1–10 Torr plume expansion is in accordance with the shock wave model, while at 760 Torr the expansion follows the drag model. On the other hand, the expansion dynamics of the Al²⁺ component, measured by introducing a band pass optical filter in the detection system, fits to the shock wave model for the entire pressure range of 10⁻² Torr to 760 Torr. The expansion velocities of the whole plume and the Al²⁺ component have been measured in vacuum. These dynamics studies are of potential importance for applications such as laser-driven plasma accelerators, ion acceleration, pulsed laser deposition, micromachining, laser-assisted mass spectrometry, ion implantation, and light source generation.