Precision lifetime measurements of a single trapped ion with ultrafast   laser pulses
  We report precision measurements of the excited state lifetime of the $5p$ $^2P_{1/2}$ and $5p$ $^2P_{3/2}$ levels of a single trapped Cd$^+$ ion. The ion is excited with picosecond laser pulses from a mode-locked laser and the distribution of arrival times of spontaneously emitted photons is recorded. The resulting lifetimes are 3.148 $\pm$ 0.011 ns and 2.647 $\pm$ 0.010 ns for $^2P_{1/2}$ and $^2P_{3/2}$ respectively. With a total uncertainty of under 0.4%, these are among the most precise measurements of any atomic state lifetimes to date. 
D. L. Moehring, B. B. Blinov, D. W. Gidley, R. N. Kohn Jr., M. J.   Madsen, T. D. Sanderson, R. S. Vallery, C. Monroe