Theoretical and experimental characterization of CO2 CPP fs CARS for high-temperature and high-pressure diagnostics

We presented a theoretical model designed to account for collisional line-mixing (LM) effects in order to provide an accurate characterization of femtosecond (fs) coherent anti-Stokes Raman scattering (CARS) spectroscopy for CO under high-temperature and high-pressure conditions. Numerical simulations revealed that the closely spaced rotational transitions within each CO vibrational manifold induced significant collisional line-mixing. This phenomenon led to a narrowing of the bandwidth of the entire vibrational manifold, partially offsetting the collisional broadening effects. Theoretical derivations further suggested that, for a relatively short probe delay (4-9 ps), a high-pressure CO chirped probe pulse (CPP) fs CARS spectrum could be precisely modeled by utilizing transition information extracted from atmospheric pressures. This proposition was substantiated through experimental measurements conducted in an atmospheric-pressure laminar flame over a temperature range of 300-1922 K, as well as in a high-pressure and high-temperature gas cell (HPHTC) at pressures up to 69 atm and preset temperatures reaching 805 K. The results indicated that CO CPP fs CARS held promise as an ideal diagnostic tool for high-pressure environments.