We study, using a combination of experiment and theory, the excitation and decay of very high-n (n ∼ 280-430) strontium autoionizing Rydberg states formed by near-resonant driving of the 5s 2 S 1/2 → 5p 2 P 1/2 core-ion transition. The branching ratio between decay through radiative transitions and through autoionization is explored. Autoionization rates are measured as a function of both the n and ℓ quantum numbers of the Rydberg electron. The non-stationary decay dynamics is studied by creating and manipulating Rydberg wave packets and by varying the laser pulse that drives the core excitation.

The destruction of high-n, n ∼ 300, strontium atoms contained in a hot atomic beam through Rydberg-Rydberg collisions is examined. The Rydberg atoms are initially created, under blockade conditions, in a localized volume and their subsequent motions lead to creation of a string of Rydberg atoms. The Rydberg atoms, however, are formed with a thermal distribution of velocities resulting in Rydberg-Rydberg collisions which lead to their destruction. The experimental data are interpreted using classical trajectory Monte Carlo techniques that simulate the excitation of the Rydberg atoms together with their subsequent motions. Using calculated collisional ionization cross sections and blockade radii, the model yields results in good agreement with experiment. The results highlight the important role collisional destruction can play when attempting to study (long-range) Rydberg-Rydberg interactions in a hot atomic beam.

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The use of autoionization as a tool to quantitatively analyze transitions between high-n strontium Rydberg states with low-to-intermediate values of L is described and is demonstrated through observations of Rabi oscillations when driving 5snf 1F3 → 5s(n + 1)g 1G4, 5snf 1F3 → 5s(n + 2)h 1H5, and 5snp 1P1 → 5s(n + 1)d 1D2 transitions using microwave fields. The technique is shown to offer advantages when compared to selective field ionization and can be used with other alkaline-earth and alkaline-earth-like metals.

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