We report an experimental study of the collective coupling of three-level atoms with a cavity mode and a free-space laser field. The measurement of the cavity transmission with a weak probe field coupled into the cavity mode reveals three spectral peaks: two sidebands and a central peak, which is produced by the coherent interaction of the free-space field with individual atoms and the collective interaction of the multiple atoms with the cavity mode. The experimental results agree with a simple calculation based on the classical light transmission through a cavity containing multiple atoms coherently driven by a free-space laser.
(c) 2009 Optical Society of America