Preferential vaporization and plasma shielding during nano-second laser ablation

Preferential removal of components from mixed material targets and plasma shielding are studied by using inductively coupled plasma-atomic emission spectrometry (ICP-AES) during UV nano-second laser ablation. The ICP emission intensity for Cu and Zn during ablation of brass samples varies versus laser power density. A model using thermal evaporation and inverse Bremsstrahlung processes is presented. The model shows that plasma shielding occurs at approximately 0.3 GW/cm2, in agreement with experimental data for change in the mass ablation rate. The good agreement of model and experimental data suggest that thermal effects are important during nano-second laser ablation for power density less than 0.3 GW/cm2.