The Autler-Townes Effect in Molecules: Observations, Theory, and Applications

In recent years experimental investigations in the field of quantum optics have expanded from atomic to molecular systems despite orders of magnitude weaker oscillator strengths and complex relaxation pathways in molecules that represented serious challenges in the past. The richness of molecular excitation pathways and the variety of molecules has made it possible to develop novel high resolution spectroscopic applications of various quantum optics tools. The present work discusses spectroscopic investigations of several diatomic alkali molecules based on the Autler-Townes effect created by application of a " strong" continuous wave coupling laser field. We demonstrate how the Autler-Townes effect can be used to control molecular angular momentum alignment. We also show that the Autler-Townes split line shape, combined with accurate measurement of the coupling laser electric field amplitude, can be used to determine absolute magnitudes of the electronic transition dipole moment matrix elements. These in turn can be used to map out the internuclear distance dependence of the electronic transition dipole moment function . μe(R). For weaker electronic transitions this method, combined with calibrated and normalized intensity measurements, makes it possible to overcome the traditional systematic complications associated with emission line strength and lifetime measurements. The former only yields a relative transition moment function and the latter frequently involves more than one transition dipole moment function. We also demonstrate that the electric field amplitude in the coupling laser Rabi frequency can be used as a " tuning" mechanism for the mixing coefficients of molecular energy levels that are weakly perturbed by the spin-orbit interaction. This makes it possible to use the Autler-Townes effect to control the valence electron spin polarization, i.e., the spin multiplicity of some molecular quantum states.