The cavity enhanced absorption spectroscopy using a tunable diode laser was applied to plasma torch diagnostics. Using cavity mirrors with 99.95% reflectance, the sensitivity was successfully enhanced by three orders of magnitude compared with the conventional single-pass laser absorption spectroscopy. With a 0.6m distance cavity, the spatial resolution of less than 1mm was achieved. The deviation of deduced temperature was below 5% when ten profiles were averaged. Total amount of data acquisition needed for a given plume section was estimated at 100M Sample. The torch plume was found in nonequilibrium electronic excitation state.
