Index of Refraction Fluctuation Spectra in Aerothermochemical Non-equilibrium Shock Layers

Focused laser differential interferometry (FLDI) was used to quantify the index of refraction amplification in the shock layer downstream of a Mach stem normal shock. The experiments were performed in the Hypervelocity Expansion Tunnel (HXT) at Texas A&M University. The Mach number was set at 8.5 and the stagnation enthalpy was varied from 3.8 to 11.0 MJ/kg, which provided a range of aerothermochemical non-equilibrium effects. The acquired data showed a clear trend of increasing index of refraction fluctuation levels over a 1 kHz to 5 MHz spectral range in the post-shock region as enthalpy increased.