Simultaneous planar laser-induced fluorescence and optical emission spectroscopy system with spatiotemporal resolution for arc jet flow diagnostic

Abstract Optical diagnostics are essential for capturing thermochemical dynamics in plasma flows during thermal protection system (TPS) material evaluation. We developed a simultaneous planar laser-induced fluorescence (PLIF) and optical emission spectroscopy (OES) system to address TPS thermal response assessment requirements. The PLIF system generated 226 nm laser at 500 Hz with 0.28 mJ pulse energy. This was achieved using a laser-pumped dye laser and frequency mixing unit. The configuration provided an effective excitation source for nitric oxide (NO) in arc jet flows. By optimizing light collection, imaging, and optical coupling configurations, the OES system enabled 500 Hz spectral measurements with one-dimensional spatial resolution. We successfully employed this system in an arc-heated wind tunnel to characterize spatiotemporally resolved properties of high-enthalpy flows over carbon/carbon (C/C) thermal protection material. The experiment captured NO-PLIF images and spatially resolved optical emission spectra of NO, cyanogen (CN), and molecular nitrogen ions (N + 2 ) from the C/C test sample surface under 20 MJ/kg enthalpy conditions. Rotational temperature profiles along streamwise and spanwise directions were derived through theoretical spectral fitting. Combined PLIF/OES data and flow pressure measurements revealed the temporal evolution of NO distribution, temperature, and enthalpy conditions during thermal response testing.