Quantitative estimation of OH-radical density from fluorescence decay behavior near the plasma-liquid interface by incident microscopic LIF spectroscopy

Abstract The formation and transportation of short-lived species on/within the plasma-liquid interfacial layer plays a crucial role in various applications because of their high chemical reactivity. However, the experimental detection and quantification of these short-lived species, such as OH radicals, at the gas-liquid interface still pose formidable challenges. This study confronts this challenge by employing incident microscopic laser-induced fluorescence (mLIF) method to capture the OH-LIF signals on the interfacial layer at different time moments of the post-discharge phase under high spatial resolution. The temporal evolution of OH density is subsequently quantified by fitting the OH-LIF decay behavior to a reaction-dissolution model. Results reveal that increasing the pulse width serves better to enhance OH generation on liquid surface, reaching a density of 1.25x1016 cm-3. Furthermore, the cathode-solution interface demonstrates significantly enhanced OH production compared to the anode-solution interface. These results underscore the efficacy of incident mLIF in quantitatively probing short-lived OH-radical production at the interfacial layer in pulsed-driven plasma-solution interactions, with potential applicability to other reactive species.