Metastable level lifetimes from electron-shelving measurements with ion clouds and single ions

The lifetime of the $3d^2\rm D_{5/2}$-level in singly-ionized calcium has been measured by the electron-shelving technique on different samples of rf trapped ions. The metastable state has been directly populated by exciting the dipole-forbidden $\rm 4S_{1/2} - 3D_{5/2}$ transition. In ion clouds, the natural lifetime of this metastable level has been measured to be ($1095\pm27$) ms. For the single-ion case, we determined a lifetime of ($1152\pm20$) ms. The $1\sigma$-error bars at the 2%-level have different origins for the two kinds of experiments: data fitting methods for lifetime measurements in an ion cloud and control of experimental parameters for a single ion. De-shelving effects are extensively discussed. The influence of differing approaches for the processing of the single-ion quantum jump data on the lifetime values is shown. Comparison with recent measurements shows excellent agreement when evaluated from a given method