Single ion measurement of the branching ratios of the 6P$_{3/2}$ decay in BaII

We report a new measurement of the branching ratios of the 6P$_{3/2}$ state decay of $^{138}$Ba$^{+}$ into the 5D$_{5/2}$ and 5D$_{3/2}$ states. The measurement was performed on a single ion in a linear Paul trap excited with 455 nm light from a doubled mode-locked Ti:Sapphire laser driving the 6S$_{1/2}$ -- 6P$_{3/2}$ transition, followed by detecting the ion's fluorescence on the 6S$_{1/2}$ - 6P$_{1/2}$ cooling transition. The use of a single ion in ultrahigh vacuum eliminates many of the systematics of the earlier measurements. Excluding decays directly to the ground state, we determine ratios of 0.881 and 0.118 for the 5D$_{5/2}$ and 5D$_{3/2}$ decays respectively with a 3{\%} statistical and 1{\%} systematic error. This is an improvement of a factor of three over previously reported data [1]. This level of precision is sufficient to compare to numerical calculations [2]. Work is underway to establish absolute values for all three ratios (6P$_{3/2}\to $6S$_{1/2}$, 5D$_{3/2}$, 5D$_{5/2})$ by driving a $\pi $ Rabi rotation on the 6S$_{1/2}$ -- 6P$_{3/2}$ transition with a single laser pulse. $^{1}$ Kastberg, et.al., \textit{J Opt. Soc. Am. B} \textbf{10}, 1330-6, (1993). $^{2}$ Gopakumar, G., \textit{Phys. Rev. A} \textbf{66 }032505-1-6, (2002).