The measurement of electron number density in helium micro hollow gas discharge using asymmetric He I lines

The electron number density N _e in helium micro hollow gas discharge (MHGD) is measured by means of optical emission spectroscopy (OES) techniques. The structure of MHGD is a gold–alumina–gold sandwich with 250 μm alumina thickness and 100 μm diameter hole. The electron temperature T _e and gas temperature T _g in the discharge is determined using the relative intensity of He I lines and ${{\text{N}}_2}^{+}({\text{B}}^2{\Sigma }_{\text{u}}^{+}-X^2{\Sigma }_{\text{g}}^{+})$ R branch lines in the frame of BP technique, respectively. The simple procedure based on spectral line broadening theory was developed in MATLAB to generate synthetic neutral line asymmetric profiles. The synthetic profiles were compared with an experimental He I 447.1 nm and He I 492.2 nm line to obtain N _e from the centre of a micro hollow gas discharge (MHGD) source in helium. The N _e results were compared with N _e values obtained from the forbidden-to-allowed (F/A) intensity ratio technique. The comparison confirmed higher N _e determined using a F/A ratio due to large uncertainty of the method. Applying the fitting formula for a He I 492.2 nm line derived from computer simulation (CS) gives the same N _e values as the one determined using the MATLAB procedure in this study. The dependence of N _e on gas pressure and electric current is investigated as well. (paper)