CaOH Molecular Emissions in Underwater Laser-Induced Breakdown Spectroscopy: Spatial–Temporal Characteristics and Analytical Performances

Recently, molecular emissions from the laser-induced plasma in ambient gas have gained increasing interest; however, very little is known about the case in water solutions. In this work, we investigated the spatiotemporal characteristics of molecular emissions, CaOH for instance, in underwater laser-induced breakdown spectroscopy (LIBS) by using time-resolved spectroscopy, spectral-resolved imaging, and shadowgraph techniques. It was shown that clear CaOH molecular bands can be observed in the spectrum at very early times after the laser pulse and presented a much longer lifetime and more homogeneous emission distribution compared with the Ca I and Ca II lines. Such unique characteristics of CaOH molecular emission inspired us to improve the performances of underwater LIBS by using the CaOH molecular bands instead of Ca I and Ca II lines. We demonstrated the excellent quantification results of CaOH with higher stability, less self-absorption, and reduced matrix effect. Meanwhile, the limit of detection (L...