Two-Photon Laser-Induced Fluorescence for Temperature and Density of Atomic Oxygen in a High-Temperature, Atmospheric Pressure Plasma Torch

High-temperature plasma sources are becoming an increasingly useful tool for nanomaterial synthesis and testing of hypersonic materials, however experimental measurements that probe the thermochemical environment are lacking. To address this lack of experimental data, we present temperature and density of atomic oxygen (O) in the plume of a high-temperature (~6000K) inductively-coupled plasma torch using two-photon laser-induced fluorescence (TALIF). Temperature will be extracted from two techniques: by fitting to the Boltzmann populations of the ground triplet states and from the Doppler Broadening of the absorption lines, with their results compared. The number densities are extracted by first taking the TALIF signal to the photoionization limited regime (thus creating a quenching-independent measurement), and calibrating to a known reference. To extend this technique to material testing, the temperature and number density of atomic oxygen in the boundary layer of an ablating graphite sample are also investigated. The effects of photoionization and saturation on the TALIF signal are assessed in both cases and included in the model.