Comprehensive effects of oceanic pressure and temperature on in situ LIBS signals

Laser-induced breakdown spectroscopy (LIBS) has been successfully developed into the oceanic chemical sensor for deep-sea exploration. However, the LIBS signals will be affected by marine environmental factors, and this effect has yet to be revealed in practice. In this work, the effects of oceanic pressure and temperature on in situ LIBS measurements were synthetically investigated according to the seawater spectra obtained by a LIBS system at different depths during sea trials. It is shown that the spectral features vary dramatically with depth. An approximately linear increase of line broadening with increasing depth was obtained. The emission intensities of the Na I and K I lines first increase with depth, followed by a decrease, while the emission intensity of the Ca I line gradually increases with depth. In addition, the emission intensity changes less significantly at depths less than 400 m, as the rapid decrease in seawater temperature above the thermocline slows the increase in emission intensity, while below the thermocline, it is mainly influenced by pressure. Especially, we initially modeled the relationship between LIBS signals and oceanic depth and temperature using exponential fitting, which not only deepens the understanding of the comprehensive influence of the marine environment on LIBS detection, but also facilitates the better application of LIBS technology in marine in situ qualitative and quantitative analysis.