Effect of pulse duration in multi-pulse excitation of silicon in laser-induced breakdown spectroscopy (LIBS)

The aim of this study is to investigate the mechanisms responsible for the increase in ablated mass and signal enhancement observed on multi-pulse excitation. Several experiments were designed to obtain evidence that confirms the laser-sample and/or laser-plasma interaction, with special attention to the role of the pulse width on these effects. A train of pulses, with a separation of a few microseconds between pulses, was used for laser-induced breakdown spectroscopy (LIBS) analysis. The signal emission of Si was improved by an enhancement factor of about 60 compared to conventional single-pulse LIBS (SP-LIBS). The number of spikes, their amplitude, and their pulse duration were found to be variable for different Q-switch delays. A temporal study was performed to determine whether or not a laser-plasma interaction took place. The effect of pulse width (as responsible of laser-sample interaction) was also evaluated. The results demonstrate that, although both interactions contribute to the observed effect, the process is predominantly governed by the pulse width.