Time of flight measurements of energy and density of laser induced Mg plasma ions and investigation of ablated surface morphology

Abstract

The energy and density measurements of laser induced Mg plasma ions have been performed by employing a Faraday cup as an ion collector by using the time of flight method. A Nd:YAG laser (532 nm, 8 ns) has been employed as an irradiation source at irradiances ranging from 4.5 GW/cm2 to 8.1 GW/cm2. For the first time, two distinct peaks of ions with the time delay of ns and μs have been identified for low-Z metal corresponding to fast and slow ions. It is revealed that both the energy and density of Mg plasma ions are increased with increasing laser irradiance and are decreased with the increasing distance between the collector and the target. The density of slow ions is 4–12 times higher than the density of fast ions for the selected irradiances. However, the energy of slow ions is in the range of 100's of eV and the energy of fast ions is in the range of 10's of keV. The anisotropic behavior and forward peaking of plasma are confirmed by the investigation of the angular distribution of ions. The plasma assisted laser ablated morphology is investigated by scanning electron microscopy (SEM) analysis. SEM analysis reveals the formation of cavities, cones, and spikes. The increasing trend of ion density and energy with increasing laser irradiance is correlated with the increased ablated areas and number density of cones.