Doppler-Free Spectrum of the Barium ¹ S ₀ ⁻¹ P ₁ Transition by Degenerate Four-Wave Mixing Using an Air/Acetylene Flame

Doppler-free flame spectrometry based on resonant degenerate four-wave mixing (D4WM) is shown to be an effective analytical tool for the determination of barium at high spectral resolution. Optical phase conjugation is produced in an air/acetylene flame, resulting in an optical signal that is a coherent time-reversed replica of the probe beam. The degenerate four-wave mixing spectrum of barium for the 6 s 2 1 S 0 -6 s6 p 1 P 1 transition at 18,060.19 cm −1 is collected with a linewidth of 0.08 cm −1 (FWHM) with the use of a convenient continuously flowing atmospheric-pressure flame atomizer. A preliminary detection limit of 5 μg/mL barium, while a Doppler-free linewidth is maintained at 0.08 cm −1 , is reported.