  We experimentally characterize the optical nonlinear response of a cold
atomic medium placed inside an optical cavity, and excited to Rydberg states.
The excitation to S and D Rydberg levels is carried out via a two-photon
transition in an EIT (electromagnetically induced transparency) configuration,
with a weak (red) probe beam on the lower transition, and a strong (blue)
coupling beam on the upper transition. The observed optical nonlinearities
induced by S states for the probe beam can be explained using a semi-classical
model with van der Waals' interactions. For the D states, it appears necessary
to take into account a dynamical decay of Rydberg excitations into a long-lived
dark state. We show that the measured nonlinearities can be explained by using
a Rydberg bubble model with a dynamical decay.
