Although the coherent dark state is basically a ground state affair the excited state does play a role in several aspects, the position (see Light Shift), the amplitude (preparation rate), and the width (destruction rate). We have performed detailed studies of these issues for two experimental configurations with respect to the tuning of the VCSEL modulation sidebands:

1. Carrier on the F=4 component, upper 9.2 GHz sideband on the F=3 component of the cesium D₂ line
2. Carrier on the F=3 component, lower 9.2 GHz sideband on the F=4 component of the cesium D₂ line

The most obvious influence of the excited states is a change in line shape when the detuning of the lasers from the optical resonance is changed (see figure).

A detailed investigation of these changes allows one to see that the contrast of the dark resonance is maximum when the strong carrier is tuned to the strongest transition into the excited state. For instance, in the case (1) above this is the F=4->F'=4 transition. On the other hand, the resonance width is maximum when the carrier is most strongly interacting with one of the "bad" excited states F'=2 or F'=5. In case (1) this is when the carrier is tuned to the F=4->F'=5 transition. You can find the full account in one of our publications: on that web page you can also find a nice picture of the results mentioned in this paragraph.