On the possibility of simultaneous temperature, species, and electric field measurements by coupled hybrid fs/ps CARS and EFISHG

Abstract

Optical signals of gas temperature, species concentration, and electric field are monitored in simple mixtures at room temperature and in the fuel-rich region of a hydrogen diffusion flame. A two-beam pure-rotational coherent anti-Stokes Raman scattering (CARS) approach was utilized for the temperature and species detection, where the combined pump/Stokes pulse doubled as the electric field induced second harmonic generation (EFISHG) pump for the electric field detection. Time-averaged EFISHG signals in environments with argon, nitrogen, oxygen, hydrogen, and air were found to match the relative hyperpolarizabilities of the molecules tabulated in literature. Measurements in a dynamic H₂-air environment represented the ability to monitor the signal dependence of species on a single-shot basis. Time-averaged EFISHG signals in different thermal environments showed the expected ∝1T² EFISHG signal dependence when also correcting for relative H₂/N₂ concentrations. Finally, measurements in a flame showed the ability to monitor the EFISHG signal dependence on the gas temperature on a single-shot basis in a plasma discharge environment.