Development of a continuous-wave, fluorescence-based two-color O₂ temperature and concentration diagnostic

Spatially resolved measurements of temperature and molecular oxygen concentration are needed to understand hypersonic phenomena such as vibrational relaxation, dissociation, and recombination. To address this need, the present work develops and demonstrates a two-color, fluorescence-based diagnostic capable of measuring both of these key quantities in repeated experiments. The diagnostic leverages a narrow-linewidth, continuous-wave laser source to probe the Schumann-Runge bands of O₂ near 225 nm behind reflected shock waves. Measured absorption cross-sections and normalized fluorescence signals show good agreement with computational models, exhibiting an average discrepancy of 10.1% and 6.9% for absorption and fluorescence, respectively. Demonstration measurements show good agreement with expected post-shock conditions and exhibit average 2σ temperature and O₂ number density uncertainties as low as 8.5% and 5.4%, respectively.