A new technique for measuring the concentration of species from the modulation dip of the nonresonant background of broad-band CARS spectra has been proposed. To reduce the mode noise superimposed on the CARS spectra, we used a modeless laser generating amplified spontaneous emission as the Stokes beam of the broad-band CARS. The modulation dip induced by a minor species, CO in Ar, was numerically calculated and fitted as a function of CO concentration and temperature. We applied this technique in measuring CO concentration in a static cell and also the profile of CO concentration in a CH4/air premixed flame of a counterflow burner.
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