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Detection of carbon monoxide (CO) in combustion gases by tunable diode laser spectrometry is often hampered by spectral interferences from H2O and CO2. A methodology for assessment of CO in hot, humid media using telecommunication distributed feedback lasers is presented. By addressing the R14 line at 6395.4  cm(-1), and by using a dual-species-fitting technique that incorporates the fitting of both a previously measured water background reference spectrum and a 2f-wavelength modulation lineshape function, percent-level concentrations of CO can be detected in media with tens of percent of water (c(H2O)≤40%) at T≤1000 °C with an accuracy of a few percent by the use of a single reference water spectrum for background correction.

We give a simple two-transition model of Faraday modulation spectrometry (FAMOS) addressing the electronic X(2)Π(ν('') = 0) - A(2)Σ(+)(ν(') = 0) band in nitric oxide. The model is given in terms of the integrated line strength, S, and first Fourier coefficients for the magnetic-field-modulated dispersive line shape function. Although the two states addressed respond differently to the magnetic field (they adhere to the dissimilar Hund coupling cases), it is shown that the technique shares some properties with FAMOS when rotational-vibrational Q-transitions are targeted: the line shapes have a similar form and the signal strength has an analogous magnetic field and pressure dependence. The differences are that the maximum signal appears for larger magnetic field amplitudes and pressures, ∼1500 G and ∼200 Torr, respectively.