Abstract

Plasma diagnostics based on saturated fluorescence and absorption spectroscopy with a semiconductor (diode) laser are developed to probe the 4s³P₁ → 4p³D₂ transition (8425 Å) of argon in an atmospheric pressure plasma produced by an inductively coupled plasma torch. Spatially resolved measurements of saturation intensity, nonradiative collisional transfer (quench) rate, and fluorescence yield (Stern–Volmer factor) are inferred from variations of spectral profile characteristics (line shape, line-center value, and frequency-integrated signal) with laser intensity. The results obtained by using fluorescence and absorption spectroscopy are mutually consistent in the analytical region 10 mm above the induction coil. The measured quench rates compare favorably with computed rates from a multilevel collisional radiative model that assumes a suprathermal electron population relative to the local thermodynamic equilibrium value at the kinetic temperature.

© 1993 Optical Society of America

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