Two-Photon Laser-Induced Fluorescence Measurements of Atomic Oxygen Density in Hypersonic Plasma Flow

An experimental investigation of high-enthalpy air flow generated by L2K arc-jet facility of DLR is carried out by means of two-photon absorption laser-induced fluorescence (TALIF) measurements of atomic oxygen at O⁢  3p⁢  P1,2,03 transition. The experiment has been conducted with an arc current of 600 A, a mass flow rate of 36  g/s, and a total pressure of 105  Pa, resulting in both mass-specific enthalpy of ∼8.4  MJ/kg and a reservoir temperature of 4200 K. Atomic oxygen has been characterized in terms of translational temperature and absolute number density either in the freestream or behind a shock wave upstream a blunt body. A calibration method based on TALIF measurements of xenon at 6p′[3/2]2 transition has been used. The results highlight that in the freestream the fluorescence signal exhibits a peak activity lower with respect to that inspected in the shock layer. The measured lifetimes of τOF=25.8  ns and τOSL=11.4  ns indicate that, in the shock layer, the depletion of the atomic oxygen excited...