Frequency Domain Control by the Autler-Townes Effect

In recent years Quantum Optics has been expanded from atomic to molecular systems despite much weaker oscillator strengths and complex relaxation pathways that have presented serious challenges in the past. The richness of molecular excitation pathways and the variety of molecular interactions combined with the Autler-Townes (AC Stark) effect has made it possible to develop novel applications in this field,\footnote{E. H. Ahmed et al., Adv. At., Mol., Opt. Phys., Vol. 61, 467 - 514, (2012).} such as control of molecular angular momentum alignment\footnote{J. Qi, \textit{et al.}, PRL 83, 288-291 (1999).} and the electronic transition dipole moment function.\footnote{J. Qi, \textit{et al.}, PRL 88, 173003 (2002).} In addition, the electric field amplitude of the control laser Rabi frequency can be used as a ``tuning'' mechanism for the mixing coefficients of energy levels that are weakly perturbed by the spin-orbit interaction,\footnote{E. H. Ahmed, \textit{et al.}, PRL 107, 163601 (2011).} i.e. to control the valence electron spin polarization and the spin multiplicity of molecular quantum states. Experimentally we demonstrate that the enhancement of the spin-orbit coupling between a pair of weakly interacting singlet-triplet rovibrational levels depends on the Rabi frequency (laser power) of the control laser. We will discuss how this mechanism can be used to optimize collisional population flow between singlet and triplet electronic states, through such control of the spin-orbit perturbation based gateway levels.