Spatially and Thermally Resolved Detection of Carbon Ablation Products From High-Power Laser Ablation of Graphite

In this paper, we investigate high temperature graphite ablation visualized using a low-pressure glow discharge environment, to experimentally emulate conditions relevant to hypersonic flight. A 2 kW continuous-wave laser is used to ablate a graphite target within a vacuum chamber at 3 Torr, while a glow discharge plasma, maintained by a 1.5 kV potential across 32.0 mm-spaced electrodes, interacts with the ablation products. Optical emission spectroscopy (OES) is employed to detect emitted photons, and the temperature of the rear surface is monitored with a thermal camera. A 2D axisymmetric heat transfer model is used to reconstruct front-surface temperatures. Emission spectra confirm the presence of key carbonaceous species, including C₂, CN, and CO, with spectral features consistent with expected transitions. Results show distinguishable changes in emission spectra between plasma with and without ablation, with contributions from molecular bands such as the C₂ Swan band and CN violet band. The CO Angstrom band was also detected. By reconstructing the plasma EEDF from ratios of excited N2 bands, we can estimate the number densities of carbon-containing ablation products. The method enables spatial resolution of species concentration gradients, providing a potential experimental platform for validating or modifying existing kinetic mechanisms for carbon-based ablating materials in a hypersonic flow.