Double-pulse LIBS in bulk water and on submerged bronze samples

In this work laser-induced breakdown spectroscopy (LIBS) has been applied in bulk water using a double-pulse laser source. As in the case of former experiments in air, the use of the double-pulse technique allows for enhancing line emission intensity and reducing the duration of the continuum spectrum, thus increasing the overall analytical performances of the technique. Tap water analysis of Na and Mg dissolved cations has been performed to investigate the capability of the technique, but most significant results have been obtained in determining the composition of submerged bronze targets by laser ablation of their surface in seawater. When the plasma is generated by double-pulse laser, the ablated matter is strongly confined by the water vapor inside the cavitations bubble. The confinement of the plasma leads to higher values of excitation temperature and holds the conditions suitable for chemical analysis (homogeneity and LTE) longer than what happens in gaseous media. The double-pulse experiments performed directly in bulk water point out the features of LIBS technique for real analytical applications in situ, such as the water quality assessment and the investigation of irremovable submerged objects.