Electrical Characterization Of Carbon Plasma Generated By Excimer Laser Ablation Of Graphite

The vacuum expansion of a transient carbon plasma produced by KrF excimer laser at moderate fluences is investigated by separating different types of ions with an electrostatic energy analyzer. In the retarding field of the analyzer, the ion current reveals a multi-peak structure and the signal deconvolution allows obtaining information on the ion abundance and thermal velocity. A significant increase of C2+ and C1+ fast ions production with the laser pulse energy is observed, while the amount of slower singly charged ions in the thermal plasma part is less affected by the irradiation conditions. By time-integration of the recorded current, the total collected charge vs. retarding potential characteristic is built and a derivative method allows obtaining the energy distribution function on the plasma plume axis, in good agreement with the shifted Maxwell-Boltzmann distribution. Future developments of this method are possible through comparison with theoretical fractional ion populations.