Splitting of atom-cavity polariton peaks for three-level atoms in an optical cavity

We explore the high-density, nonlinear regime of atom-cavity coupling for a gas of three-level atoms at high temperature inside an optical cavity, interacting with the cavity field and a strong driving field. We find a region of parameters where the two side peaks in the transmission spectrum (which, in the linear regime, are associated with "bright polaritons") split into two pairs of peaks. Experimental results are presented along with a theoretical model that indicates that this phenomenon is unique to the three-level system in the large Doppler-broadening regime.