Measurement of the branching ratio in the 6P3∕2 decay of BaII with a single trapped ion

We present a measurement of the branching ratios from the $6{P}_{3∕2}$ state of $\mathrm{Ba}\phantom{\rule{0.2em}{0ex}}\mathrm{II}$ into all dipole-allowed decay channels ($6{S}_{1∕2}$, $5{D}_{3∕2}$, and $5{D}_{5∕2}$). Measurements were performed on single $^{138}{\mathrm{Ba}}^{+}$ ions in a linear Paul trap with a frequency-doubled mode-locked Ti:sapphire laser resonant with the $6{S}_{1∕2}\ensuremath{\rightarrow}6{P}_{3∕2}$ transition at $455\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ by detection of electron shelving into the dark $5{D}_{5∕2}$ state. By driving a $\ensuremath{\pi}$ Rabi rotation with a single femtosecond pulse, an absolute measurement of the branching ratio to $5{D}_{5∕2}$ state was performed. Combined with a measurement of the relative decay rates into $5{D}_{3∕2}$ and $5{D}_{5∕2}$ states performed with long trains of highly attenuated $455\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ pulses, it allowed the extraction of the absolute ratios of the other two decays. Relative strengths normalized to unity are found to be $0.756\ifmmode\pm\else\textpm\fi{}0.046$, $0.0290\ifmmode\pm\else\textpm\fi{}0.0015$, and $0.215\ifmmode\pm\else\textpm\fi{}0.0064$ for $6{S}_{1∕2}$, $5{D}_{3∕2}$, and $5{D}_{5∕2}$, respectively. This approximately constitutes a threefold improvement over the best previous measurements and is a sufficient level of precision to compare to calculated values for dipole matrix elements.