A simple profile-fitting method to determine the metastable and resonant densities in a cold atmospheric pressure argon plasma jet

A simple profile-fitting method is applied to determine the concentrations of metastable and resonant species in a cold atmospheric pressure argon plasma jet. This method is based on the analysis of the effect of self-absorption broadening on the profiles of spectral lines emitted from plasma. The Argon lines which correspond to transitions to metastable and resonant lower states were measured with high resolution optical emission spectroscopy. Fitting the measured line contours yields line-integrated densities (N-l x L) of metastable Ar(1s(5)) and Ar(1s(3)) of 1.2 x 10(5) m(-2) and 5.0 x 10(14) m(-2), respectively. For resonant species, it is difficult to perform a good density-estimation by fitting measured line contours because of the broad intrinsic resonant line shape and the low resonant densities in the plasma. Top-limits of 4.8 x 10(15) m(-2) and 7.2 x 10(14) m(-2) are estimated for resonant states Ar(1s(2)) and Ar(1s(4)), respectively. By comparing the fittings of metastable and resonant lines, it is found that the applicability of the profile-fitting routine is sensitive to the line-center optical thickness of emission lines (mainly determined by the lower states densities) and the sharpness of intrinsic line profiles of corresponding transitions. (C) 2011 American Institute of Physics. [doi:10.1063/1.3643004]