Comparison of low-pressure DC glow discharge and dielectric barrier discharge in CO2-laser mixture by optical emission spectroscopy

Abstract

Nowadays the CO2 lasers are used in many technologies, including medicine and material processing industry. Besides original low-pressure low-power lasers pumped by DC glow discharge, the attention is focused on the high power atmospheric pressure lasers. We use optical emission spectroscopy to study both low pressure (from 266 Pa to 1330 Pa) DC glow discharge (DC GD) and the dielectric barrier discharge (DBD) (from 5 kPa to 100 kPa) in mixtures of helium, nitrogen and carbon dioxide used in CO2 lasers.Considering the emission spectrum of the discharges mentioned above, we can find bands of the first and the second positive systems of the nitrogen molecule. From these bands it is possible to deduce energetic balance and the vibrational temperature [1].In our contribution, the vibrational temperature of nitrogen is determined by means of optical emission spectroscopy from the second positive system band of the nitrogen molecule for various discharge currents in DC glow discharge and for various gap widths in DBD. Using these two discharges we covered the whole pressure range from 266 Pa up to atmospheric pressure. The dependence of the vibrational temperature on N2 content in the mixture is also investigated. The vibrational temperature showed a steady decrease with increasing pressure in whole pressure range. It was found, that the vibrational temperature of nitrogen in the DC GD is twice as high as in the DBD, which was attributed to the different nature of discharges.Spectroscopic measurements were complemented with measurements of electric properties of discharges: the longitudinal electric field strength for DC glow discharge and Lissajous' figures for DBD [1,2].