Measurement of Ar resonance and metastable level number densities in argon containing plasmas

The resonance 1s(4) (P-3(1)), 1s(2) (P-1(1)) and metastable 1s(5) (P-3(2)), 1s(3) (P-3(0)) level number densities of argon are determined by means of the branching fraction method in an inductively coupled plasma at 5 Pa and 10 Pa in argon with admixture of hydrogen, nitrogen and oxygen. The 1s(5) (P-3(2)) densities are compared to laser absorption spectroscopy measurements to evaluate the reliability of the branching fraction method and its limitations. The results are in good agreement and the use of a compact, low cost, low resolution spectrometer (Delta lambda = 1.3 nm) is sufficient to reliably determine the first four excited states of argon in argon-hydrogen and argon-oxygen mixtures. The addition of nitrogen results in unreliable densities, as the observed argon lines overlap with emission of the N-2(B-3 Pi(g) -A(3)Sigma(+)(u)) transition.