Normal mode line shapes for atoms in standing-wave optical resonators

A high finesse standing-wave cavity mode resonantly interacting with a beam of two-level Ba-138 atoms is weakly driven by a tunable laser. With mean intracavity atomic number, [(N) over bar] approximate to 1, we observe one-, two-, and three-peaked line shapes for strong coupling. In addition, two-peaked spectra observed in intermediate coupling demonstrate that line-shape splitting is not necessarily indicative of oscillatory atom-cavity energy exchange. Several atoms are required for [(N) over bar] approximate to 1, so this is not a true single-atom regime.