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Isotope shifts of the 4s 2 1 S 0 → 4s5p 1 P 1 transition and hyperfine splitting of the

We present a measurement of the lifetime of the metastable 3d 2 D 5/2 state in the 40 Ca + ion, using the so-called shelving technique on a string of five Doppler laser-cooled ions in a linear Paul trap. A detailed account of the data analysis is given, and systematic effects due to unwanted excitation processes and collisions with background gas atoms are discussed and estimated. From a total of 6805 shelving events, we obtain a lifetime = 1149± 14͑stat. ͒ ±4͑sys. ͒ms, a result which is in agreement with the most recent measurements.

Ion Coulomb crystals form when trapped ions are cooled below a certain critical temperature. In radiofrequency (RF) traps, such crystals are usually stationary (i.e. non-rotating) with shapes similar to those of cold, homogeneously charged liquids when the number of ions is sufficient for three-dimensional structures to appear. 'Dynamically stable' structures can, however, also be created either by directly applying a torque to an initially stationary crystal or by choosing trap parameters just within the stability region where stationary crystals will melt due to parametric resonances between the RF trap field and ion plasma modes.