Radiation and temperature fields of the continuum field are determined by using different spectroscopic methods based on the spectral emission of an argon plasma jet. An interferential filter of bandwidth 2.714 nm centred at a wavelength of 633 nm is used to observe only the continuum emission and to eliminate the self-absorption phenomenon. An optical multichannel analyser (OMA) of an MOS detector is used to measure argon plasma jet volumetric emissivity under atmospheric pressure and high temperatures. An emission spectroscopic method is used to measure the Stark broadening of the hydrogen line H β and to determine the electron density. The local thermodynamic equilibrium is established and its limit is stated. The local electron temperature is determined by two methods (the continuum emission relation and the LTE relations), and the total Biberman factor is measured. The results given by the OMA are compared with those given by the imagery method. At a given wavelength, the Biberman factor, which depends on the electron temperature and the electron density, may serve as an indicator to show where the LTE prevails along the argon plasma jet core length.

The imagery method is used to detect the radiation flux emitted by an optically thin argon plasma jet at atmospheric pressure and high temperatures, after assuming conditions of local thermodynamic equilibrium in the continuum field. Quantitative agreement is observed by comparing the results of the imagery method with those from a multichannel optical detector. Abel inversion is programmed to convert the intensity measured by both methods to the volumetric emissivity of the argon plasma jet. The results presented in the form of intensity and volumetric emissivity show that the imagery method remains a good way of characterizing an argon plasma jet.