From single pulse to double pulse ns-Laser Induced Breakdown Spectroscopy under water: Elemental analysis of aqueous solutions and submerged solid samples

In this paper the developments of Laser Induced Breakdown Spectroscopy (LIBS) underwater have been reviewed to clear up the basic aspects of this technique as well as the main peculiarities of the analytical approach. The strong limits of Single-Pulse (SP) LIBS are discussed on the basis of plasma emission spectroscopy observations, while the fundamental improvements obtained by means of the Double-Pulse (DP) technique are reported from both the experimental and theoretical point of view in order to give a complete description of DP-LIBS in bulk water and on submerged solid targets. Finally a detailed description of laser-water interaction and laser-induced bubble evolution is reported to point out the effect of the internal conditions (radius, pressure and temperature) of the first pulse induced bubble on the second pulse producing plasma. The optimization of the DP-LIBS emission signal and the determination of the lower detection limit, in a set of experiments reported in the current scientific literature, clearly demonstrate the feasibility and the advantages of this technique for underwater applications.