Atomic oxygen is measured in a pulsed dielectric barrier discharge (DBD) using two-photon absorption laser-induced fluorescence (TALIF). The ground-level atomic oxygen is excited to the 3p 3P state by two-photon absorption at 226 nm. Negative (−40 kV) or positive (+30 kV) pulsed DBD occurs in an O2–N2 mixture at atmospheric pressure. The pulse width of the DBD current is approximately 50 ns. The TALIF experiment shows that the decay rate of atomic oxygen increases linearly with O2 concentration. This result proves that atomic oxygen decays mainly by the third-body reaction, O + O2 + M → O3 + M. The rate coefficient of the third-body reaction is estimated to be 2.2 × 10−34 cm6 s−1 in the negative DBD and 0.89 × 10−34 cm6 s−1 in the positive DBD. It is shown that the decay rate of atomic oxygen increases linearly with humidity. This can explain the well-known fact that ozone production in DBD is suppressed by increasing humidity.

Atomic oxygen is measured in the afterglow of pulsed positive corona discharge using time-resolved two-photon absorption laser-induced fluorescence. The discharge occurs in a 14 mm point-to-plane gap in dry air. After the discharge pulse, the atomic oxygen density decreases at a rate of 5×104 s−1. Simultaneously, ozone density increases at almost the same rate, where the ozone density is measured using laser absorption method. This agreement between the increasing rate of atomic oxygen and decreasing rate of ozone proves that ozone is mainly produced by the well-known three-body reaction, O+O2+M→O3+M. No other process for ozone production such as O2(v)+O2→O3+O is observed. The spatial distribution of atomic oxygen density is in agreement with that of the secondary streamer luminous intensity. This agreement indicates that atomic oxygen is mainly produced in the secondary streamer channels, not in the primary streamer channels.

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Various kinds of optical diagnosis for atmospheric pressure non-thermal plasma which the authors have examined experimentally, are explained. They are LIF of OH (248nm excitation), NO (226nm), TARIF of O (225nm), Sclieren image, ozone profile observation by the laser absorption, spectrum analysis of the plasma including NO-emission, and streamer propagation. The last can be controlled by the gated IICCD camera but others are controlled by the laser emission which makes possible to observe the time change after the plasma. Those data propose the O generation in the streamer region which produces the ozone or VOCs oxidation. O radical is now a very important parameter as the VOCs decomposition, especially, related with the catalyst effect.