Quantum cascade laser absorption spectroscopy with the amplitude-to-time conversion technique for atmospheric-pressure plasmas

Yumii, T., Kimura, N., and Hamaguchi, S., Journal of Applied Physics 113(21), 213101 (2013) http://doi.org/10.1063/1.4808261
The NO2 concentration, i.e., density, in a small plasma of a nitrogen oxide (NOx) treatment reactor has been measured by highly sensitive laser absorption spectroscopy. The absorption spectroscopy uses a single path of a quantum cascade laser beam passing through a plasma whose dimension is about 1 cm. The high sensitivity of spectroscopy is achieved by the amplitude-to-time conversion technique. Although the plasma reactor is designed to convert NO in the input gas to NO2, it has been demonstrated by this highly sensitive absorption spectroscopy that NO2 in a simulated exhaust gas that enters the reactor is decomposed by the plasma first and then NO 2 is formed again, possibly more than it was decomposed, through a series of gas-phase reactions by the time the gas exits the reactor. The observation is consistent with that of an earlier study on NO decomposition by the same type of a plasma reactor [T. Yumii, J. Phys. D 46, 135202 (2013)], in which a high concentration of NO2 was observed at the exit of the reactor. © 2013 AIP Publishing LLC.