In this paper, we present an optical study of the A 3∑u+ state of N2 produced in an inductively coupled plasma. The operation of the discharge was characterized using ion flux measurements and broadband optical emission, and a clear change from capacitively to inductively coupled behaviour was observed with increasing applied power. The typical ion flux at 100 W and 10 mTorr was found to be 1.8×1018 m2 s-1, from which a N 2+ ion density of ∼1.5×109 cm -3 was inferred. Diode laser cavity enhanced absorption spectroscopy (CEAS) was used to probe the A3∑u+ state via the B3πg(ν = 3) ← A 3∑u+(ν = 0) band at 686 nm. P 33 band head spectra were used to determine both the translational (Ttr) and rotational (Trot) temperatures of the molecules at the v = 0 level. These were found to be in equilibrium but dependent on plasma parameters; in a 10 mTorr discharge, Trot ≈ Ttr, varying from ∼300 K at 5 W to ∼450 K at 400 W applied power. Absolute number densities in individual spin-rotation states were determined by calibrating the CEAS technique using the cavity ringdown time to measure the mirror reflectivity. The overall population in the v = 0 level was found to be (1.19 ± 0.07)×1010 cm-3 under typical conditions of 100 W radio frequency power and 10 mTorr pressure, corresponding to a discharge efficiency for the production of this level of ∼10 -5. A kinetic scheme is presented to account for the pressure and power dependence of the A-state concentration in the v = 0 level.
