Diagnostics of laser ablated plasma plumes

The effect of an ambient gas on the expansion dynamics of laser ablated plasmas has been studied for two systems by exploiting different diagnostic techniques. First, the dynamics of a MgB2 laser produced plasma plume in an Ar atmosphere has been investigated by space-and time-resolved optical emission spectroscopy. Second, deposition rate and fast ion probe measurements have been used to study the plume propagation dynamics during laser ablation of a silver target, over a large range of Ar background gas pressures (from high vacuum to approximate to 100 Pa). A comparative analysis of the experimental results allows us to identify different regimes of the plume expansion, going from a free plume at low pressure, through collisional and shockwave like hydrodynamic regimes at intermediate pressure, finally reaching a confined plume with subsequent thermalization of the plume particles at the largest pressure of the background gas. The experimental findings also show that a combination of complementary techniques, like optical emission spectroscopy, close to the target, and fast ion probe and deposition rate measurements at larger distances, can lead to a more detailed understanding of the laser ablated plasma plume propagation in a background gas. (C) 2003 Elsevier B.V All rights reserved.