Spatiotemporal evaluation of plasma parameters during LIBS analysis for on- line sorting of zinc-based alloy

In the present work, plasma generated by fundamental radiation from a Q-switched Nd:YAG laser focused onto a zinc based alloy is studied spectroscopically. The quantification of the zinc based alloy using the calibration free- laser induced breakdown spectroscopy (CF-LIBS) is only possible under the assumption of local thermodynamic equilibrium (LTE). In this study, we investigated the spatiotemporal evolution of plasma parameters (T e , N e ) as well as the spatiotemporal evaluation of LTE in order to find regions where LTE is valid. For an accurate plasma temperature estimation, only times ranging from 0.8 µs to 6 µs and for axial distance from 0.6 to 2.6 mm were chosen. The electron temperature values were calculated using the Saha-Boltzmann method applied on neutral and singly ionized copper lines, while the electron number density was calculated using the Stark broadened profile of the H α line using the relation of Gigosos.