Influence of excited-state hyperfine structure on ground-state coherence

In a three-level Λ system, a bichromatic light field can induce a ground-state coherence that leads to vanishing absorption of the bichromatic field. Although this coherence is between ground states only, in a real atom it can nevertheless be influenced by the hyperfine structure of the excited state. We present experimental results which show that for suitable detunings of the bichromatic field from optical resonance, the specific contribution of each individual hyperfine level of the excited state can be distinguished through increased amplitude or width of the ground-state coherence.