Application of Coherent Anti-Stokes Raman Scattering (CARS) Technique to the Detection of NO

A coherent anti-Stokes Raman scattering (CARS) setup has been developed to detect contamination of atmospheric nitrogen by nitric oxide (NO). To allow spatially resolved measurements and the possibility of utilizing windows close by the test volume, we chose the folded BOXCARS setup with a CARS lens of focal length 0.5 m and a diameter of 80 mm. A frequency-doubled Nd:YAG laser (= 532 nm; EL = 50 mJ; L = 10 ns; repetition rate, 10 s−1; bandwidth, 0.05 cm−1) serves as pump for a dye laser (Ep = 25 mJ; EL = 2 mJ; bandwidth, 0.03 cm−1), which is tunable between 585 and 615 nm. Nitric oxide CARS spectra including the first hot band have been measured with high spectral resolution in a temperature range from 300 to 800 K. The detection limit of NO is on the order of 0.25% in nitrogen under atmospheric pressure. With suppression of the nonresonant background in the application of polarization CARS, the detection limit could not be scaled down in a desirable manner. The comparison between measured and calculated CARS spectra of NO in an N2 surrounding confirms the reliability of the energy matrix elements and the Lorentzian width of the type (p, T = 0.06(298 K/T)0.6 p/p0 cm−1.

[1]  J. K. Dixon.  The Absorption Coefficient of Nitrogen Dioxide in the Visible Spectrum , 1940 .

[2]  G. J. Rosasco,et al.  Rotational collisional narrowing in the NO fundamental Q branch, studied with CW stimulated Raman spectroscopy , 1984 .

[3]  G. Guelachvili,et al.  Infrared study of the X2Π ν = 0, 1, 2 levels of 14N16O. Preliminary results on the ν = 0, 1 levels of 14N17O, 14N18O, and 15N16O , 1978 .

[4]  S. Uchida,et al.  Soot elimination and NO/sub x/ and SO/sub x/ reduction in diesel-engine exhaust by a combination of discharge plasma and oil dynamics , 1992 .

[5]  J. W. C. Johns,et al.  Λ-Doubling in the v = 2 ← 0 overtone band in the infrared spectrum of NO☆ , 1979 .

[6]  M. Kushner,et al.  Gas-Phase Removal of Nitric Oxide from Gas Streams Via Dielectric Barrier Discharges , 1992 .

[7]  J. Reid,et al.  The vibration-rotation fundamental of NO , 1977 .

[8]  Larry A. Rahn,et al.  Background-free cars studies of carbon monoxide in a flame , 1979 .

[9]  P. K. Falcone,et al.  Tunable diode laser measurements of the band strength and collision halfwidths of nitric oxide , 1983 .

[10]  M. Péalat,et al.  Determination of N2(X) vibrational level populations and rotational temperatures using CARS in a D.C. low pressure discharge , 1987 .

[11]  R. Teets.  Accurate convolutions of coherent anti-Stokes Raman spectra. , 1984, Optics letters.

[12]  H. W. Schrötter,et al.  Raman Scattering Cross Sections in Gases and Liquids , 1979 .

[13]  A. K. Hui,et al.  Rapid computation of the Voigt and complex error functions , 1978 .

[14]  A. G. Maki,et al.  Heterodyne frequency measurements on the nitric oxide fundamental band , 1986 .