Lifetime of the $7s6d$ ${{}^{1}D}_2$ atomic state of radium

The lifetime of the $7s6d$ ${{}^{1}D}_2$ state of atomic radium is determined to be $385\left(45\right)\mu \text{s}$ using cold ${}^{226}\text{R}\text{a}$ atoms prepared in a magneto-optical trap. The ${{}^{1}D}_2$ state is populated from the decay of the ${{}^{1}P}_1$ state which is excited by a pulse of 483 nm light. The decay of the ${{}^{1}D}_2$ state is observed by detecting delayed fluorescence at 714 nm from the last step in the decay sequence ${{}^{1}P}_1\text{−}{{}^{1}D}_2\text{−}{{}^{3}P}_1\text{−}{{}^{1}S}_0$. The measured lifetime is compared to a number of theoretical calculations. An improved value of the $7s7p$ ${{}^{1}P}_1$ level of $20715.598\left(6\right){\text{cm}}^{-1}$ is obtained.

Figure 1

(Color online) Level diagram for the lowest eight electronic states of neutral radium. The lifetimes of ${{}^{1}D}_2$ and ${{}^{3}P}_1$ are experimentally determined; other lifetimes and branching ratios are based on theoretical calculations [2, 6].

Figure 2

(Color online) (a) Suppression of MOT fluorescence at 714 nm caused by 483 nm light pumping radium to metastable states. This panel represents data accumulated for 11 min with the MOT beams kept on. (b) 714 nm flash following 483 nm excitation of radium atoms shows the decay of ${{}^{1}D}_2$. The MOT beams are off for the collection of these data. This panel represents data accumulated for 10 h with the timing structure in (c).