High-speed mid-infrared laser absorption spectroscopy of CO[Formula: see text] for shock-induced thermal non-equilibrium studies of planetary entry

A high-speed laser absorption technique is employed to resolve spectral transitions of CO[Formula: see text] in the mid-infrared at MHz rates to infer non-equilibrium populations/temperatures of translation, rotation and vibration in shock-heated CO[Formula: see text] - Ar mixtures. An interband cascade laser (DFB-ICL) resolves 4 transitions within the CO[Formula: see text] asymmetric stretch fundamental bands ([Formula: see text] v[Formula: see text] = 1) near 4.19 [Formula: see text] . The sensor probes a wide range of rotational energies as well as two vibrational states (00[Formula: see text] 0 and 01[Formula: see text] 0). The sensor is demonstrated on the UCLA high enthalpy shock tube, targeting temperatures between 1250 and 3100 K and sub-atmospheric pressures (up to 0.2 atm). The sensor is sensitive to multiple temperatures over a wide range of conditions relevant to Mars entry radiation. Vibrational relaxation times are resolved and compared to existing models of thermal non-equilibrium. Select conditions highlight the shortcomings of modeling CO[Formula: see text] non-equilibrium with a single vibrational temperature.