The Effect of Cerium Surface Oxidation on Plasma Plume Geometry Imaged After Nanosecond Laser Ablation *

The effects of surface chemistry on plasma formation and expansion after laser ablation are of interest to applications from metallurgy to astrophysics. In this work, we investigated cerium plasma plume geometry as a function of surface oxidation by imaging the plasma emission. Polished cerium was ablated using a Nd:YAG nanosecond pulsed laser. Images were stitched from a series of EMCCD gated delay times from 10 ns to 3 µs after pulse with the imaging repeated as the surface oxidized for 30 min, 1 hour, 1.5 hours, 3 hours, etc. up to a week later. Images of the plume compared at different oxidation states for the same CCD delay time show significant changes of both plasma length and overall geometry. As the metal surface oxidized, the velocity of the expanding shockwave was calculated and showed a decrease in velocity as the metal surface oxidized.