Transient probe spectra in strongly driven atoms and their dependence on initial atomic conditions

We analyze the transient probe spectra that arise when a three-level atom is strongly driven by an optical field nearly resonant with one transition and is probed by a step-function weak field on a coupled transition. We pay particular attention to the effect of imbalances in the initial dressed-state populations on the observed spectra. As recently pointed out, such imbalances may be induced by sudden changes in the phase of the driving field. We find that transient probe spectra may differ dramatically for different initial atomic conditions. We follow the temporal relaxation of these novel probe spectra to their steady-state form. Our calculations do not include the effect of inhomogeneous broadening and are hence appropriate to studies of collimated atomic beams.