Autler-Townes spectroscopy of the5S1/2−5P3/2−44Dcascade of cold85Rbatoms

We study nonlinear optical effects in the laser excitation of Rydberg states. 5S 1 / 2 and 5 P 3 / 2 levels of 8 5 Rb are coupled by a strong laser field and probed by a weak laser tuned to the 5P 3 / 2 -44D Rydberg resonance. We observe high contrast Autler-Townes spectra which are dependent on the pump polarization, intensity, and detuning. The observed behavior agrees with calculations, which include the effect of optical pumping.