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.