A 3.0 GHz pulsed microwave source operated at atmospheric pressure with a pulse power of 1.4 MW, a maximum repetition rate of 40 Hz, and a pulse length of 3.5 µs is experimentally studied with respect to the ability to remove NO x from synthetic exhaust gases. Experiments in gas mixtures containing N 2 /O 2 /NO with typically 500 ppm NO are carried out. The discharge is embedded in a high-Q microwave resonator, which provides a reliable plasma ignition. Vortex flow is applied to the exhaust gas to improve gas treatment. Concentration measurements by Fourier transform infrared spectroscopy confirm an NO x reduction of more than 90% in the case of N 2 /NO mixtures. The admixture of oxygen lowers the reductive potential of the reactor, but NO x reduction can still be observed up to 9% O 2 concentration. Coherent anti-Stokes Raman scattering technique is applied to measure the vibrational and rotational temperature of N 2 . Gas temperatures of about 400 K are found, whilst the vibrational temperature is 3000-3500 K in pure N 2 . The vibrational temperature drops to 1500 K when O 2 and/or NO are present. The randomly distributed relative frequency of occurrence of selected breakdown field intensities is measured by a calibrated, short linear-antenna. The breakdown field strength in pure N 2 amounts to 2.2 × 10 6 V m −1 , a value that is reproducible within 2%. In the case of O 2 and/or NO admixture, the frequency distribution of the breakdown field strength scatters more and extends over a range from 3 to 8 × 10 6 V m −1 .

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A coherent anti-Stokes Raman scattering (CARS) set-up has been developed to study the reduction of nitric oxide (NO) by a microwave-generated nitrogen plasma under atmospheric pressure. A frequency-doubled Nd:YAG laser provides two pump beams at nm and excites a dye laser, which is tunable between 588 and 615 nm. Density and temperature profile measurements of in the cylindrical microwave discharge by the common CARS technique deliver an axis temperature of 7000 K at P = 800 W input power. The detection of a minority of NO in under atmospheric pressure by CARS is limited to a concentration of 2500 ppm. By applying polarization-sensitive CARS the detection limit can be scaled down to 200 ppm. This technique is used to examine the reduction of NO in a reaction chamber fed by vibrationally excited and N entering the chamber through a nozzle. Behind the nozzle most of the NO is decomposed. An overall reduction efficiency for NO of 65-85% was found, decreasing with growing NO concentration.