A study of underwater stand-off laser-induced breakdown spectroscopy for chemical analysis of objects in the deep ocean
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 μs, whereas the lifetime of the laser-induced plasma was only a few μs. The effect of water temperature and the influence of the underwater optical path on the LIBS signal have also been evaluated.