Eur. Phys. J. D (2012) 66: 281
https://doi.org/10.1140/epjd/e2012-30474-8

Regular Article

Absolute OH density determination by laser induced fluorescence spectroscopy in an atmospheric pressure RF plasma jet

¹ College of Electrical and Electronic Engineering, HuaZhong University of Science and Technology, WuHan, Hubei 430074, P.R. China
² Department of Applied Physics, Research Unit Plasma Technology, Ghent University, Sint-Pietersnieuwstraat 41, B4, 9000 Ghent, Belgium
³ Institute of Solution Chemistry of the Russian Academy of Science, Academicheskaya St., 1, Ivanono, 153045, Russia
⁴ Chimie des Interactions Plasma-Surface (ChIPS), CIRMAP, Université de Mons, 20 place du Parc, 7000 Mons, Belgium
⁵ Materia Nova Research Center, Parc Initialis, 7000 Mons, Belgium

^a e-mail: anton.nikiforov@ugent.be

Received: 30 July 2012
Received in final form: 25 September 2012
Published online: 15 November 2012

Abstract

In this paper, the ground state OH density is measured in high pressure plasma by laser-induced fluorescence (LIF) spectroscopy. The OH density determination is based on the simulation of the intensity fraction of fluorescence from the laser-excited level of OH (A) in the total detected LIF signal. The validity of this approach is verified in an atmospheric pressure Ar  +  H₂O plasma jet sustained by a 13.56 MHz power supply. The transition line P₁ (4) from OH (A,v′ = 1,J′ = 3) → OH   (X,v′′ = 0,J′′ = 4) is used for the LIF excitation. The absolute OH density is determined to be 2.5 × 10¹⁹ m^-3 at 1 mm away from the jet nozzle. It corresponds to a dissociation of 0.06% of the water vapor in the working gas. Different mechanisms of OH (X) production in the core of the plasma jet are discussed and analyzed.