Langmuir probe investigation of transient plasmas generated by femtosecond laser ablation of several metals: Influence of the target physical properties on the plume dynamics

Abstract

Langmuir probe measurements were performed on transient plasmas generated by femtosecond laser ablation of several metallic targets (Al, Cu, Mn, Ni, In, Te, W). The analysis of current-voltage characteristics at various delays after the laser pulse gave access to the temporal evolution of ion density, electron temperature and plasma potential. The time-of-flight profile of the current recorded by the probe was also discussed in terms of a shifted Maxwell-Boltzmann velocity distribution, considering both thermal and drift velocities. The plasma parameters derived by these approaches were correlated with the electrical conductivity of the investigated metals. Assuming a direct dependence between the probe ionic signal and the charge carrier mobility in the target, a logarithmic fit was proposed for the plasma potential variation with electrical conductivity, whereas a derivative of this function was applied for the electron temperature. The saturation charge derived from the time-integrated probe ionic signals was influenced by the electrical conductivity of the target and also by the atomic weight of the metal. A steep increase of the thermal and drift velocities with conductivity was observed.