MEASURING THE CONCENTRATION OF MINOR SPECIES FROM THE MODULATION DIP OF THE NONRESONANT BACKGROUND OF BROAD-BAND CARS SPECTRA

A new technique for measuring the concentration of species from the mo dulation dip of the nonresonant background of broad-band CARS spectra has been proposed. To reduce the mode noise superimposed on the CARS s pectra, we used a modeless laser generating amplified spontaneous emis sion as the Stokes beam of the broad-band CARS. The modulation dip ind uced by a minor species, CO in Ar, was numerically calculated and fitt ed 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 counterfl ow burner.