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 ¹³⁸Ba atoms is weakly driven by a tunable laser. Transmitted and sidelight scattered line shapes are recorded. With mean intracavity atomic number, 〈N̄〉≈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 〈N̄〉≈1, so this is not a true single-atom regime.