POLARIZATION-SENSITIVE COHERENT ANTI-STOKES-RAMAN SCATTERING APPLIED TO THE DETECTION OF NO IN A MICROWAVE-DISCHARGE FOR REDUCTION OF NO

A coherent anti-Stokes Raman scattering (CARS) set-up has been develop ed to study the reduction of nitric oxide (NO) by a microwave-generate d nitrogen (N-2) plasma under atmospheric pressure. A frequency-double d Nd:YAG laser provides two pump beams at lambda = 532 nm and excites a dye laser, which is tunable between 588 and 615 nm. Density and temp erature profile measurements of Na in the cylindrical microwave discha rge 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 Ng und er atmospheric pressure by CARS is limited to a concentration of 2500 ppm. By applying polarization-sensitive CARS the detection limit can b e scaled down to 200 ppm. This technique is used to examine the reduct ion of NO in a reaction chamber fed by vibrationally excited N-2 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.