Spectral diagnosis of gas temperature of atmospheric pressure plasma jet in helium

For atmospheric pressure plasma jets (APPJ), the gas temperature is essential for their applications. A spectral diagnosis of APPJ's gas temperature is conducted in this work. The optical emission spectra of helium APPJ are captured by using an optical spectrometer system. Then, the grating secondary spectrum of OH (A²∑⁺(ν'=0) → X²Π(ν″=0)) are used to diagnose the gas temperature of plasmas because the spectrum has excellent resolution. Meanwhile, the vibrational temperatures are estimated by using the vibration sequence of N₂ band (SPS, the second positive system). On the basis of the method, some important conclusions were obtained. First, the spectral identifying indicates that the grating primary spectrum covers a whole wavelength range from 200 nm to 900 nm, and that the grating secondary spectrum overlaps with the primary spectrum from 400 nm to 900 nm. Second, the gas temperature (about 320 K) is close to the room temperature, while the vibrational temperature of the N₂ (SPS) is about 5000 K. The trend of the two temperatures changing with the applied voltage is discussed in the end.