Optical emission and Langmuir probe diagnostic measurements in DC electrode pulse discharge in nitrogen

Optical emission of selected nitrogen bands is analyzed for different nitrogen fill pressure and input electrical power to find the changes in spectral intensities with changing discharge conditions. The electron temperature $T_e$ is inferred from the intensity ratio $(I^+_{BX}/I_{CB})$ of $(0$–$0$, $391.44$ nm$)$ and $(0$–$2$, $380.49$ nm$)$ band heads whereas electron number density $n_e$ from the intensity ratio and the corresponding rate coefficient $X~($cm$^3$ s$^{–1})$ for the given temperatures. Both band heads belonging to the first negative system and second positive system of nitrogen have a different threshold of excitation energies, and therefore the corresponding emission intensities provide a direct correlation between the group of electrons involved in optical emission (a part of electron energy distribution function above the excitation and ionization thresholds) and electron temperature. Measured intensity ratio $(I^+_{BX}/I_{CB})$ and resulting $T_e$ both increase with input power and decrease with gas fill pressure following almost the same trend. Besides, time-averaged triple probe measurements have been performed to determine $T_{\mathrm{eff}}$ and $n_e$ under the same discharge conditions for the sake of comparison. The spectroscopic method provides the variation of $T_e$ and $n_e$ at various discharge power and gas pressure in comparison with probe measurements. This study will help to optimize the discharge conditions in terms of active species concentration, electron temperature and electron number density for technological applications.