Dephasing of ultracold cesium 80D_5/2-Rydberg electromagnetically induced transparency

We study Rydberg electromagnetically induced transparency (EIT) of a cascade three-level atom involving 80D_5/2 state in a strong interaction regime employing a cesium ultracold cloud. In our experiment, a strong coupling laser couples 6P_3/2 to 80D_5/2 transition, while a weak probe, driving 6S_1/2 to 6P_3/2 transition, probes the coupling induced EIT signal. At the two-photon resonance, we observe that the EIT transmission decreases slowly with time, which is a signature of interaction induced metastability. The dephasing rate γ_OD is extracted with optical depth OD = γ_ODt. We find that the optical depth linearly increases with time at onset for a fixed probe incident photon number R_in before saturation. The dephasing rate shows a nonlinear dependence on R_in. The dephasing mechanism is mainly attributed to the strong dipole-dipole interactions, which leads to state transfer from nD_5/2 to other Rydberg states. We demonstrate that the typical transfer time τ_0(80D) obtained by the state selective field ionization technique is comparable with the decay time of EIT transmission τ_0(EIT). The presented experiment provides a useful tool for investigating the strong nonlinear optical effects and metastable state in Rydberg many-body systems.