Temperature and NO density measurements by LIF and OES on an atmospheric pressure plasma jet

Laser-induced fluorescence (LIF) is used to determine the density and rotational temperature of the nitric oxide (NO) X ground state in a microwave plasma jet. The jet is operated in ambient air with a flow of helium mixed with 0–6% air. The applied microwave power is 18–55 W. The obtained temperatures are compared with rotational temperatures of the NO A excited state and the N2 C state, obtained with optical emission spectroscopy. The temperatures obtained with optical emission spectroscopy (OES) are found to be approximately 30% higher than those obtained with LIF. This suggests that the common assumption that the rotational distribution of the excited state is thermalized within the effective lifetime might not be correct. The absolute density of NO X is measured in situ with 1 mm spatial resolution, and is found to have a maximum of about 1.4 × 1021 m−3.