We present a precise measurement of the lifetime of the
6p 2P1/2o excited state of a single trapped ytterbium ion
(Yb+). A time-correlated single-photon counting technique is used, where ultrafast pulses excite the ion and the emitted photons are coupled into a single-mode optical fiber. By performing the measurement on a single atom with fast excitation and excellent spatial filtering, we are able to eliminate common systematics. The lifetime of the
6p 2P1/2o state is measured to be $8.12\ifmmode\pm\else\textpm\fi{}0.02\text{ }\text{ns}$, in good agreement with previous experimental measurements and some theoretical values.
We report the first observation of the atomic cascade $9^{1}P_{1}\ensuremath{-}7^{3}S_{1}\ensuremath{-}6^{3}P_{1}$ in mercury. The exponential distribution of time delays between detection of the $9^{1}P_{1}\ensuremath{-}7^{3}S_{1}$ (5676-\AA{}) photon and the $7^{3}S_{1}\ensuremath{-}6^{3}P_{1}$ (4358-\AA{}) photon was measured, and a value of 8.2(0.2) nsec was obtained for the mean lifetime of the
73S1 level.