Excitation Dynamics of Interacting Rydberg Atoms in Lithium Magneto-Optical Trap

We study the time-resolved Rydberg excitation dynamics for Lithium atoms confined in a magneto-optical trap. Loss of neutral atoms due to Rydberg excitation is measured by means of analyzing the absorption of a weak probe beam. Our experiment demonstrates the existence of both density-dependent excitation blockade and excitation facilitation effects. Moreover, we measure the frequency shift of the Rydberg transition at various durations of excitation pulses. This frequency shift can be attributed to the formation of ultracold ions from the high-density ensemble of Rydberg atoms.