Abstract
A tunable diode laser has been applied in optical Stark-modulated absorption spectroscopy to provide spatially resolved concentration measurements of CO. A cw IR probe beam from the diode laser was crossed with a nonresonant high-intensity beam from a Nd:YAG laser to generate a Stark-induced change in absorption in the crossing volume. The optical Stark-modulated absorption spectra were calculated showing the influence of experimental parameters including partial pressure of CO, total absorption path length, and intensity of the perturbing beam. The technique was demonstrated in a premixed atmospheric CH4–air flame and in a room temperature absorption cell, and good agreement was found between experiment and theoretical calculations. Thus far a spatial resolution of 0.5 cm has been achieved for time-averaged measurements of CO flame mole fractions of a few percent. Further improvements in the system should enable measurements of CO levels approaching 0.1% in flames with spatial resolution in the mm range and temporal resolution of 10 nsec.
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