Determination of the branching of theP11Ba i level from studies of the intensity dependence of resonance fluorescence

The resonance fluorescence from the ${}_{}{}^{138}{}_{}{}^{}\mathrm{Ba}$ I 5535-Å 6${\mathit{s}}^{21}$ ${\mathit{S}}_0$-6s6p ${}_{}{}^1{}_{}{}^{}$ ${\mathit{P}}_1$ transition has been measured as a function of incident intensity using a Doppler-free atomic beam geometry and a single-mode cw dye laser. The upper ${}_{}{}^1{}_{}{}^{}\mathrm{P}_1^{}{}_{}{}^{}$ level has a weak branch to intermediate metastable D states. A long laser-atom interaction region was used, which ensured that essentially all atoms could be pumped into the D states during their transit through the laser beam. By analyzing the shape of the saturation curve a value for the branching ratio to the 6s5d ${}_{}{}^1{}_{}{}^{}$,3D levels of (3.57±0.38)×${10}^{\mathrm{-}3}$ has been obtained.