Single-shot common old ordinary Raman scattering for time-resolved one-dimensional hypersonic flow diagnostics

Common old ordinary Raman scattering (COORS) is revisited to evaluate its applicability for hypersonic flow characterization. Due to its very low cross-section, Raman scattering is often considered unsuitable for measuring low-pressure gas properties that are found in ground test simulations of high-altitude hypersonic flights. Utilizing a recently developed one-dimensional (1D) light scattering technique with a volume Bragg grating filter and Stokes side band windowing, we demonstrate 1D rotational Raman measurements of temperature and neutral gas density across a bow shock in front of a blunt wedge model under Mach 6 hypersonic flow. The experiment was conducted in the Hypervelocity eXpansion Tunnel (HXT) at Texas A&M University. The measurements were successfully obtained during a single run of the tunnel operation, capturing the temperature and density distributions with dynamic ranges of 200 - 2000 K and 5x10²³ - 4x10²⁴ /m³ respectively, over both the freestream and post-shock regions, covering approximately 10 mm in length with a spatial resolution of < 0.5 mm. Time-resolved high-speed measurement capability at 100 kHz was also demonstrated, showcasing the robustness of 1D COORS for gas diagnostics.