Spectroscopy and imaging of laser-induced plasmas for chemical analysis of bulk aqueous solutions at high pressures

Laser-induced breakdown spectroscopy (LIBS) is a chemical sensing technique that has been demonstrated in numerous applications on land. This study investigates the application of LIBS as a technique for in situ analysis of the chemical composition of the ocean. The effects of pressure on the spectral emissions of various different elements in bulk aqueous solution has been evaluated, and imaging of plasmas generated in liquids at pressures between 0.1-30 MPa has been performed. The observations indicate that during the early stages of laser-induced breakdown, in the time frame when spectroscopic measurements are made, the plasma and surrounding phenomena (formation of shockwaves and cavitation bubbles) are almost independent of the surrounding hydrostatic pressure up to 30 MPa. Spectroscopic investigations found that Na, Ca, and Mg are detectable in liquid at pressures from 0.1 to 30 MPa, at concentrations of 1, 10, and 500ppm, respectively. These elements are of key importance in the identification of hydrothermal vent fluids. The results of this study suggest that laser induced spectroscopy is applicable for in situ elemental analysis of liquids at oceanic pressures.