DURIP 98/99 Spectroscopic Diagnostics for Atmospheric Pressure Air Plasmas

摘要

The goal of this project was to develop laser-based diagnostics employing the cavity ring-down spectroscopy (CRDS) technique for the investigation of trace quantities of molecular species in hostile environments such as atmospheric pressure air plasmas. As part of a continuing collaboration with the nonequilibrium plasma chemistry program of Prof. Charles Kruger at the Stanford High Temperature Gasdynamics Laboratory, we have successfully applied CRDS in determination of temperature and ground state population gradients of transient species such as ions and radicals generated in plasma environments. This noninvasive absorption diagnostic provided information on ground-state populations that complemented information on excited state populations provided by emission spectroscopy. A prototype CRDS setup was implemented to examine N2(+) concentration profiles in a 50 kW air plasma source. Ongoing work that extends the CRDS technique into the infrared 'fingerprint' region for many of the hydrocarbon free radicals (CH3, CH2, CH, C2H, etc.) generated in an arc jet plasma-deposition reactor has provided interesting results on the temperature of species present in this hostile environment. These investigations have also identified technical obstacles that limit the sensitivity and spatial resolution of the CRDS technique in such harsh environments.