Laser-Assisted Dissolution of Geological Samples Submerged in Water: Evidence of Hydrothermal Processing*

We investigate the use of a 240 ns pulse Nd:YLF (3 kHz, 0.33 mJ/pulse) laser to rapidly break down and dissolve an obsidian sample submerged in water. We propose a mechanism, a hydrothermal surface interaction, by which this laser-assisted dissolution process occurs. The laser fluence is below the ablation thresholds, 0.4-7 J/cm²vs 10 J/cm²and is directed onto the submerged sample causing an increase in temperature and pressure at the water-sample interface. Our results indicate that this process is highly efficient at removing, and potentially dissolving, amorphous glassy substrates (i.e. an obsidian sample) at the water-sample interface. This is further shown by the formation of purified SiO₂structures that reform on the surface post-pulse. We additionally show how various parameters (e.g. dwell time, power, repetition rate, and focal length) affect the efficiency of this process.