Number density and temperature measurements obtained using sensitive diode laser spectroscopy in an argon plasma

The absolute concentration and translational temperature of the 2p₁₀ and 2p₇ excited states of argon have been measured in an inductively coupled plasma chamber under a variety of operating conditions using both calibrated diode laser frequency modulation spectroscopy and cavity enhanced absorption spectroscopy. Accurate lineshape analysis of frequency modulation signals has been employed to extract the desired information, and is corroborated by cavity enhanced measurements. Temperatures are found to vary linearly with pressure from ∼400 K at 20 mTorr (2.7 Pa) to ∼510 K at 90 mTorr (12 Pa) in a 200 W discharge while concentrations peak at 3.25×10⁸ cm^-3 at 30 mTorr (4 Pa) (also in a 200 W discharge). The uncertainty in the recovered temperature is 7%, dominated by uncertainties in the calibration of the frequency scale. PACS 42.62Fi; 52.70kz