Autler-Townes spectroscopy of the 5S_(1/2)-5P_(3/2)-44D cascade of cold ⁸⁵Rb atoms

We study nonlinear optical effects in the laser excitation of Rydberg states. $5S_{1/2}$ and $5P_{3/2}$ levels of $^{85}$Rb are strongly 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.