Resonance broadening as a valuable diagnostic to study atmospheric pressure plasma – application to micro-plasmas
Résumé
Low temperature atmospheric pressure discharges have shown their uniqueness to convert electrical energy and matter to a rich reactive chemistry together with ionizing and energetic radiations leading to a growing pool of applications [1]. Among those plasma sources, micro-hollow cathod discharges(MHCD) and atmospheric pressure plasma jets (APPJ) have been developped and offer complementary features. With the motivation to elaborate industrial plasma processes, diagnostics are essential to understand and control the main plasma parameters. Optical emission spectroscopy is an intuitive and flexible approach to study the discharge. In this contribution, one will report on an original method to determine the gas temperature [2] and some hydrodynamic propeties [3] through the analyses of resonnant transitions. Recorded lineshapes of resonant atomic emissions are broaden due to the dipole-dipole interaction occuring when the emiting atom is coupled to the ground state of its collider. The resonant broadening often overlaps with other mechanisms such as van der Waals interactions or the instrumental profile. Figure 1 evidences the sensitivity of the resonant transition of He to hydrodynamic effects induced by the guided ionization waves (GIW) which propagate trough a tube and expand into the ambiant air [3].
The analysis of the lineshapes will be presented also in the case of silicon-based MHCD to reveal the temperature gradient in the vicinity of a plasma ignited in a 100 µm cavity. The results obtained in various gas mixtures will be compared and disccussed with the measured rotational temperature of N2.
References:
[1]C. Tendero, C. Tixier, P. Tristant, J. Desmaison, and P. Leprince, Spectrochimica Acta Part B: Atomic Spectroscopy 61, 2 (2006).
[2]S. Iseni, R. Michaud, P. Lefaucheux, G. B. Sretenović, V. S. der Gathen, and R. Dussart, Plasma Sources Sci. Technol. 28, 065003 (2019).
[3]S. Iseni, C. Pichard, and A. Khacef, Appl. Phys. Lett. 115, 034102 (2019).