Measurements of single-state and state-ensemble lifetimes of high-lying Rb Rydberg levels

We demonstrate a hybrid method based on field ionization and state-selective deexcitation capable of measuring the lifetimes of high-lying Rydberg levels. For nS Rydberg states of Rb atoms with principal quantum number 60<=n<=88, we measure both the lifetimes of single target states and those of the ensembles of Rydberg states populated via blackbody-radiation-induced transitions. We find good overall agreement with numerical calculations of the expected lifetimes in both cases. However, for the target-state lifetimes, we find a local deviation towards shorter lifetimes for states around n=72, which we interpret as a signature of a modified blackbody spectrum in the finite volume in which our experiments take place.