Non-equilibrium CARS Thermometry for Plasmas

In this work we present non-equilibrium temperature measurements using hybrid fs/ps Coherent Anti-Stokes Raman Scattering (CARS). Experimental CARS spectra were measured in a low temperature plasma reactor. The experimental CARS spectra is fitted with synthetic CARS spectra to determine vibrational temperature dynamics in the N₂ gas within the plasma. Additionally, changes in ro-vibrational CARS signal intensity were used to determine gas density which is used to infer gas temperature. A parametric study on the plasma reactor was performed where the plasma pressure, RF power, and acetylene flow rate were modified. When comparing the measured vibrational temperatures with the gas temperatures, the plasma consistently exhibits significant thermal non-equilibrium.