Dynamics of atomic sublevel coherences during modulated optical pumping

The dynamics of coherences between sublevels of an electronic ground state is investigated under conditions of modulated optical pumping. It is shown that the modulation corresponds to an effective reduction of the apparent sublevel splitting, thereby allowing the excitation of coherences between atomic sublevels whose energy splitting would require very high laser intensities for dc excitation. In addition, the frequency and phase of the modulation introduce additional degrees of freedom that can be utilized for the design of new experiments. The theoretical evaluations are compared with experiments on the ground state of atomic sodium.