An atmospheric pressure plasma jet (APPJ) using radio-frequency (13.56 MHz)power has been developed to produce homogeneous glow discharge at low temperature. Withoptical emission spectroscopy, we observed the excited species (atomic helium, atomic oxygen andmetastable oxygen) generated in this APPJ and their dependence on gas composition ratio andRF power. O and O2(b1Σg+ ) are found in the effluent outside the jet by measuring the emissionspectra of effluent perpendicular to the jet. An interesting phenomenon is found that there is anabnormal increase of O emission intensity (777.4 nm) between 10 mm and 40 mm away from thenozzle. This observation result is very helpful in practical operation.
