Multi-normal-mode splitting of a cavity in the presence of atoms: A step towards the superstrong-coupling regime

Multi-normal-mode splitting peaks are experimentally observed in a system with Doppler-broadened two-level atoms inside a relatively long optical cavity. In this system, the atom-cavity interaction can reach the superstrong-coupling condition with atom-cavity coupling strength g root N to be near or larger than the cavity free-spectral range Delta(FSR). In such case, normal-mode splitting can occur in many cavity longitudinal modes to generate the multi-normal-mode splitting peaks, which can be well explained by the linear-dispersion enhancement due to the largely increased atomic density in the cavity. Many new interesting phenomena might come out of this superstrong atom-cavity coupling regime.