Time-resolved optical emission spectroscopy of laser-produced air plasma

Abstract

Time-resolved optical emission spectroscopy (OES) is used to analyze a mesh-initiated air breakdown plasma induced by a transverse excitation atmospheric CO2 pulsed laser (λ=10.591 μm, 64 ns (full width at half maximum), 70-160 J/ cm2). Emission from excited N, O, C, H, and Ar; ionic fragment N+, O+, N2+, O2+, C+, and molecular band systems of N2+ (B 2 ∑u+ -X 2 ∑g+; D 2II g -A 2 IIu), N2 (C 3II u -B 3II g), and OH (A 2∑ + -X 2II) is observed. Plasma characteristics are examined in detail on the emission lines of N+, O+, and C by time-resolved OES technique. The results show a faster decay of continuum and ionic spectral species than of neutral atomic and molecular ones. The velocity and kinetic energy distributions for the different species were obtained from time-of-flight measurements. Excitation temperature and electron density in the laser-induced plasma were estimated from the analysis of spectral data at various times from the laser pulse incidence. Temporal evolution of electron density has been used for the estimation of the three-body recombination rate constant. © 2010 American Institute of Physics.