Spatially resolved spectroscopical characterization of one- and two-component structured femtosecond laser induced plasmas

Femtosecond-laser ablation is becoming increasingly popular due to its advantageous characteristics such as reduced fractionation and improved lateral resolution. However, since the emission from the resulting laser-induced plasmas is reduced and relatively short-lived, optical spectroscopy analyses with fs lasers (LIBS) are often carried out with enhancement strategies, such as double-pulse LIBS. For orthogonal double pulse set ups, characterizing the spatio-temporal excitation of the fs-LIP can be useful to fully optimize the scheme. This work aims to characterize the structure of a fs-laser induced plasma in atmospheric pressure, illustrating the general behavior of the plasma plume for different target materials (metals and dielectrics), and further obtain insight about the emission and excitation characteristics of the plume for pure copper and PVC samples. The results show a clear two-component structure of the metallic plumes, composed by a fast-displacing upper component that presents higher excitation and higher ionization degree and a slow, almost static component that remains near the sample surface throughout the complete evolution. On the contrary, PVC presented only one fast-displacing component which was seen not to be homogeneous in terms of excitation. As a general feature, in the present study conditions, all the plasma plumes induced in different samples presented an intensity-dominating fast component, with discrepancies in the presence and relative intensity of the slow component.