Time-resolved spectroscopic diagnostic of the CO2 plasma induced by a high-power CO2 pulsed laser

摘要

Laser-induced breakdown spectroscopy of CO2 plasma, initially at room temperature and pressures ranging from 6.4 to 101 kPa was investigated using a transverse excitation atmospheric CO2 pulsed laser (λ = 10.532 μm, a full width at half maximum of 64 ns, and an intensity from 1.2 to 5.6 GW cm-2). The strong emission of the CO2 plasma shows excited neutral O and C atoms and ionized O+ and C+ species. The medium-weak emission is due to electronic relaxation of excited species C2+, O2+, N+, N, H and molecular band systems of C2(E1Σg +-A 1Πu; e3Πg-a 3Πu; d3Πg-a 3Πu), CN(B2Σ+-X 2Σ+; A2Π- X2Σ+), O2(b1Σ g +-X3Σg -), O 2 +(A2Πu-X2Π g), N2(C3Πu-B3Π g) and N2 +(B2Σ u +-X2Σg +). The characteristics of the spectral emission intensities from different species have been investigated as a function of the laser irradiance and CO2 pressure. Optical breakdown threshold intensities and plasma temperatures were obtained. The evolution of the luminous plasma was examined by time-resolved optical emission spectroscopy. The velocity distributions for different species were obtained from time-of-flight (TOF) measurements. Electron density in the laser-induced plasma was estimated from the Stark broadening method. The temporal evolution of the intensities in the TOF profiles for O+, O2+, C, C+ and C2+ species has been used for the estimation of the corresponding three-body electron-ion recombination rate constants. © 2011 Elsevier B.V. All rights reserved.