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

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 ${{\gamma}_{{{\text{O}}_{2}}}}$   =  0.40  ±  0.08  cm−1/bar for oxygen molecules and ${{\gamma}_{\text{He}}}$   =  0.46  ±  0.03 cm−1/bar for helium atoms. These correspond to pressure broadening rate constants $k_{\text{PB}}^{{{\text{O}}_{2}}}$   =  9 centerdot 10–9 cm3 s−1 and $k_{\text{PB}}^{\text{He}}$   =  4 centerdot 10−9 cm3 s−1, respectively. The well-known quenching rate constants of O(3p 3 P J ) by O2 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.