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/N2/O2 flame to spectral simulations based on a two-level theory for stationary, saturable absorbers by Abrams et al. Temperatures determined from least-squares fits of simulations to experimental spectra in the A2Σ+?X2Π+(0,0) band are compared to temperatures obtained from OH absorption spectroscopy and a radiation-corrected thermocouple. We find that DFWM rotational temperatures derived from Q-branch spectra agree with thermocouple and are independent of pump laser intensity for low to moderate saturation (I≈Isat). However, the temperatures are systematically low and depend on pump intensity if the analysis neglects saturation effects. We demonstrate a method for obtaining an effective pump saturation intensity for use with the two-level model. This approach for analyzing saturated DFWM line intensities differs from previous work in that the use of the theory of Abrams et al. rather than a transition-dipole-moment power law allows treatment of a much wider range of saturation. Based on the observed signal-to-noise ratio an NO detection sensitivity of 25 ppm is projected, limited by a DFWM background interference specific to hydrocarbon flames.
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Received: 15 September 1998 / Revised version: 18 November 1998 / Published online: 24 February 1999
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Farrow, R., Rakestraw, D. Analysis of degenerate four-wave mixing spectra of NO in a CH4/N2/O2 flame . Appl Phys B 68, 741–747 (1999). https://doi.org/10.1007/s003400050697
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DOI: https://doi.org/10.1007/s003400050697