A study of underwater stand-off laser-induced breakdown spectroscopy for chemical analysis of objects in the deep ocean
F.J. Fortes, S. Guirado, A. Metzinger, J.J. Laserna, Journal of Analytical Atomic Spectrometry, 2015, 30, 1050
In this work, we demonstrate for the first time the feasibility of stand-off laser induced breakdown spectroscopy (ST-LIBS) for the analysis of distant submerged objects. The applicability of underwater stand-off LIBS is highly challenging since it involves the delivery of a focused laser pulse toward the distant target through the aqueous media and then the transmission of the light emitted by the laser-induced plasma back to the detection system. Experiments were designed to gain fundamental knowledge regarding LIBS analysis in an underwater open-path configuration. Samples were analyzed at distances up to 80 cm from the sensor at a solid-water interface. Effective plasma formation was achieved using dual pulse excitation with Nd:YAG laser pulses at 532 nm. Intense and well resolved emission signals were observed with interpulse delay times close to 500 ms, whereas the lifetime of the laser-induced plasma was only a few ms. The effect of water temperature and the influence of the underwater optical path on the LIBS signal have also been evaluated.