Saturation of the weak probe amplification in a strongly driven cold and dense atomic cloud

We present an experimental and theoretical investigation of the weak probe amplification in a cold and optically thick atomic cloud that is highly dri ven by a strong pump laser. We find that for high optical densities the pro be amplification is strongly saturated. We compare our saturation measureme nts with a model based on dressed-atom population equalization due to re-sc attering of spontaneous emission. Good agreement between theory and experim ent is obtained only when corrections due to multiple scattering are includ ed.