Assessments of lifetimes and photoionization cross-sections at 10.6 μm of nd Rydberg states of Rb measured in a magneto-optical trap

By using IR laser photoionization in a magneto-optical trap, radiative lifetimes of rubidium Rydberg nd states (n = 16–20) have been measured. The measured lifetimes are: 4.63 μs for the 16d state, 5.39 μs (17d), 6.74 μs (18d), 8.06 μs (19d) and 8.99 μs (20d). The experimental values are in agreement with previous theoretical calculations. The reported method allows also for a measurement of the photoionization cross-sections of the specified Rydberg states at 10.6 μm. In this case the experimental values (ranging from 39 Mb for the 16d state to 30 Mb for the 20d state) look inconsistent with theoretical calculations.