High-speed 1-D Raman spectroscopy for simultaneous temperature and species measurements in a transient highly underexpanded jet

A novel, to the best of our knowledge, 10-kHz 1-D Raman instrument is presented for simultaneous species number densities and temperature measurements in a non-reactive, highly underexpanded H₂ jet. The system combines a pulse-burst laser with four CCD cameras operated in burst-gating mode to achieve high-fidelity acquisition of four Raman bands (rotational S₀(1) and S₀(3) of H₂; ro-vibrational Q-branch of H₂ and N₂) at 10 kHz. A dual-line ratiometric thermometry approach, utilizing the H₂ rotational S₀(1) and S₀(3) transitions, enables temperature measurements from ambient down to the challenging cryogenic conditions. The simultaneous determination of number density and temperature fields allows further derivation of additional properties within the shock-containing flow field, including mole fractions, absolute density, and pressure. The spatio-temporal resolving capability of the instrument is demonstrated through the recording of a 2-ms transient H₂ injection event, from the startup phase to the final decay.