Absolute concentration measurements of C2 in a diamond CVD reactor by laser-induced fluorescence

By use of Laser-Induced Fluorescence (LIF) the absolute concentration of the C₂ radical in a microwave excited diamond chemical vapour deposition plasma has been measured for the first time. LIF spectra of thed³_g–a³_u (1,0) Swan band near 473 nm were recorded and synthesized theoretically allowing the plasma temperature of 2100 ± 200 K to be inferred. Quenching rates were determined from time-resolved measurements of the fluorescence decay. By calibrating the LIF detection system, using spontaneous Raman scattering in H₂ in the reactor vessel, the absolute concentration of C₂ was determined to be (7.5 ± 1.7) × 10¹⁰ cm^–3. Observations of the C₂ density under varying plasma conditions are reported.