Hybrid fs/ps CARS for non-equilibrium temperature measurements in N₂/H₂ DC glow discharges

This manuscript presents the development of a hybrid fs/ps coherent anti-Stokes Raman scattering system for rotational and vibrational temperatures measurements in a non-equilibrium N2/H2 DC plasma. A simple 3-beam configuration is used to simultaneously excite both the pure-rotational and rovibrational Raman transitions of the N₂ molecule. Vibrational population distributions of N_s(v) up to v= 9 are measured in both pure N₂ and N₂/H₂ DC discharges. Strong vibrational non-equilibrium is observed at both the anode and cathode. The results show that the anode has a stronger non-Boltzmann N₂(v) distribution. The addition of H₂ reduces the vibrationally excited N₂(v) population and increases the gas temperature. These results provide insights into the vibration-vibration (V-V′) energy transfer and vibrational-translational (V-T) relaxation of N₂(v) by H₂ in DC discharges.