TALIF measurements of oxygen atom density in the afterglow of a capillary nanosecond discharge

The atomic oxygen density has been measured in the afterglow of a capillary nanosecond discharge in 24-30mbar synthetic air (N₂ : O₂=4 : 1) by the two-photon absorption laser-induced fluorescence (TALIF) technique, combined with absolute calibration by comparison with xenon TALIF. The discharge was initiated by a train of 30ns FWHM pulses of alternating positive-negative-positive polarity, separated by 250ns, with a train repetition frequency of 10Hz. The amplitude of the first pulse was 10kV in the cable. A flow of synthetic air through the tube provided complete gas renewal between pulse trains. The O-atom density measurements were made over the time interval 200ns-2μs after the initial pulse. The gas temperature was determined by analysis of the molecular nitrogen second positive system optical emission spectrum. The influence of the gas temperature on the atom density measurements, and the reactions producing O atoms, are discussed.