Diagnosis of gas temperature, electron temperature, and electron density in helium atmospheric pressure plasma jet

The optical emission spectra of helium atmospheric pressure plasma jet (APPJ) are captured with a three grating spectrometer. The grating primary spectrum covers the whole wavelength range from 200 nm to 900 nm, with the overlapped grating secondary spectrum appearing from 500 nm to 900 nm, which has a higher resolution than that of the grating primary spectrum. So the grating secondary spectrum of OH (A ^{2 +}(υ'=0) → X ²(υ'=0)) is employed to calculate the gas temperature (T _g) of helium APPJ. Moreover, the electron temperature (T _e) is deduced from the Maxwellian electron energy distribution combining with T _g, and the electron density (n _e) is extracted from the plasma absorbed power. The results are helpful for understanding the physical property of APPJs.