Investigation of femtosecond laser-produced plasma from various metallic targets using the Langmuir probe characteristic

The Langmuir probe is used to characterize the plasma produced by fs-laser ablation from pure metallic targets. Time dependence of the probe current and the total collected charge is discussed in terms of a shifted Maxwell-Boltzmann distribution function, and from probe characteristics the plasma temperature and average charge state are calculated. Target materials of various physical properties (atomic mass, thermal constants) are used to find possible correlations with resulting plasma parameters. By positively biasing the probe, the collected charge - probe voltage characteristic is in general vertically shifted, and for low negative probe potentials an effect consisting in an abnormal decrease of the ion current is observed. Periodic falls of the total collected charge vs. probe voltage are experimentally recorded, the effect being more significant at high background pressure. They are tentatively attributed to secondary ionization. Published by AIP Publishing.