Effects of Plume Hydrodynamics and Oxidation on the Composition of a Condensing Laser-Induced Plasma

High-temperature chemistry in laser ablation plumes leads to vapor-phase speciation, which can induce chemical fractionation during condensation. Using emission spectroscopy acquired after ablation of a SrZrO₃ target, we have experimentally observed the formation of multiple molecular species (ZrO and SrO) as a function of time as the laser ablation plume evolves. Although the stable oxides SrO and ZrO₂ are both refractory, we observed emission from the ZrO intermediate at earlier times than SrO. We deduced the time-scale of oxygen entrainment into the laser ablation plume using an ¹⁸O₂ environment by observing the in-growth of Zr¹⁸O in the emission spectra relative to Zr¹⁶O, which was formed by reaction of Zr with ¹⁶O from the target itself. Using temporally resolved plume-imaging, we determined that ZrO formed more readily at early times, volumetrically in the plume, while SrO formed later in time, around the periphery. Using a simple temperature-dependent reaction model, we have illustrated that the formation sequence of these oxides subsequent to ablation is predictable to first order.