Pressure broadening of atomic oxygen two-photon absorption laser induced fluorescence

Abstract

Atomic oxygen, considered to be a determining reactant in plasma applications at ambient pressure, is routinely detected by two-photon absorption laser induced fluorescence (TALIF).Here, pressure broadening of the (2p 4 3 P 2 → 3p 3 P J=0,1,2 ) two-photon transition in oxygen atoms was investigated using a high-resolution TALIF technique in normal and Doppler-free configurations. The pressure broadening coefficients determined were O2 γ = 0.40 ± 0.08 cm −1 /bar for oxygen molecules and He γ = 0.46 ± 0.03 cm −1 /bar for helium atoms. These correspond to pressure broadening rate constants k PB O 2 = 9 • 10 -9 cm 3 s −1 and k PB He = 4 • 10 −9 cm 3 s −1 , respectively. The well-known quenching rate constants of O(3p 3 P J ) by O 2 and He are at least one order of magnitude smaller, which signifies that non-quenching collisions constitute the main line-broadening mechanism. In addition to providing new insights into collisional processes of oxygen atoms in electronically excited 3p 3 P J state, reported pressure broadening parameters are important for quantification of oxygen TALIF line profiles when both collisional and Doppler broadening mechanisms are important. Thus, the Doppler component (and hence the temperature of oxygen atoms) can be accurately determined from high resolution TALIF measurements in a broad range of conditions.

Chemical kinetics in an atmospheric pressure helium plasma containing humidity

“…Finally, the pressure broadening is determined as Δ σ L = 0.37 cm –1 from an average of several automated fits to the data using the previously specified values for Δ σ D and Δ σ I . This value is in reasonable agreement with Δ σ L = (0.46 ± 0.03) cm –1 for He measured by Marinov et al 59 in the ‘COST Reference Microplasma Jet’ using Doppler-free TALIF, albeit for a different optical transition.…”

Nanosecond pulsed humid Ar plasma jet in air: shielding, discharge characteristics and atomic hydrogen production

“…Apart from a discrepancy at 3 μs in the broadening of the absorption line which cause is unclear, both have the same temporal dependence. Marinov et al recently reported the pressure broadening of atomic oxygen TaLIF in He [65]. They showed that non-quenching collisions are responsible for the observed pressure broadening.…”

Absolute CO number densities measured using TALIF in a non-thermal plasma environment

“…At our experimental conditions, Doppler broadening is typically one order of magnitude larger than pressure broadening and similar to the laser broadening. Hence a further improvement on the resolvability of the rotational lines can be achieved by measuring Doppler-free excitation spectra, although this is experimentally challenging [5,26].…”