Fig. 7: The comparison between optical emission spectra of plasma jet and the standard spectrum under different input power (in the wavelengths range of 640–760 nm).

A–E corresponds to a specific input power: A Power = 22 kW, O2/C = 0.9, B power = 24 kW, O2/C = 0.9, C power = 26 kW, O2/C = 0.9, D power = 28 kW, O2/C = 0.9, E power = 30 kW, O2/C = 0.9.