Narrow resonances with excitation of finite bandwidth field
  The effect of the laser linewidth on the resonance fluorescence spectrum of a two-level atom is revisited. The novel spectral features, such as hole-burning and dispersive profiles at line centre of the fluorescence spectrum are predicted when the laser linewidth is much greater than its intensity. The unique features result from quantum interference between different dressed-state transition channels. 
Peng Zhou, Mao-Fa Fang, Qing-Ping Zhou, and Gao-Xiang Li