Dielectric barrier discharges (DBDs) are investigated in helium and nitrogen as a function of pressure from 5 to 1000 mbar. Different regimes are observed: glow, Townsend, multi-peak and filamentary, depending on pressure, power and electrode gap. In helium, DBD is a glow-like discharge with a transition to multi-peak or Townsend discharge at high power. In nitrogen, the discharge is Townsend-like and shows a transition to multi-peak mode below 300 mbar. Transition to filamentary mode is observed for large gaps. Fast exposure imaging is used to investigate multi-peak mode in nitrogen. Electrical measurements and time-resolved optical emission spectroscopy are used to characterize the discharge, to study the evolution of metastable species as a function of the pressure and to analyse the discharge startup. These results offer new perspectives for the operation of DBDs in low vacuum.

Emission spectra of silicon oxide molecules in the spectral range from 228 to 246 nm have been observed in a pulsed discharge and a laser-produced plasma. The vibrational bands belonging to the υ = −1, 0, +1 sequences of the SiO A 1 -X 1 + system have been reproduced by computer simulations in order to determine the vibrational and rotational temperatures. In the pulsed discharge, the vibrational temperature has been found to exceed the rotational temperature several-fold, indicating the non-thermal character of this type of plasma. In contrast, similar values of the two temperatures have been deduced for the plasma produced by pulsed-laser ablation, proving a collisional equilibrium. Simple criteria based on intensity ratio measurements are proposed for the temperature evaluation from the SiO emission bands.

UV emission of silicon oxide molecules observed from a non-thermal atmospheric pulsed dielectric barrier discharge was experimentally explored in a spectral range from 228 to 253 nm. The main vibrational bands (1, 1), (2, 2) and (0, 1) of A 1Π–X 1Σ+ electronic transition were investigated. Corresponding synthetic spectra was built up and adjusted with good agreement. Excitation temperatures (Tvib, Trot) were deduced as a function of gas composition. It is shown that the rotational temperature can represent a non-intrusive diagnostic of plasma gas temperature in process control.