Study of the optical-discharge plasma in multicomponent mixtures of molecular gases

Based on a 5-kW cw CO2 laser, an atmospheric-pressure plasmatron for the gas-phase synthesis of diamond films is fabricated. The conditions of the existence of a laser plasma in molecular gas mixtures are determined. The minimal radiation powers required for maintaining a stationary optical discharge (SOD) are measured at different concentrations of the components of Ar—CH4—H2 gas mixtures and different flow velocities. The emission spectra of the SOD plasma are measured in pure Ar and the Ar—H2—CH4 mixture along and across the propagation direction of the plasma jet. The characteristic green emission spectrum at the plasma periphery exhibits the intense lines of the C2 radical, which is responsible, in our opinion, for the formation of polycrystalline diamond films.