Resonant radiative processes
  The frequency correlation properties of the radiation from an atom in a strong field in resonance with neighboring transitions are considered. It is shown that the difference in frequency correlation in two-photon and stepwise processes decreases with increase of the external field. The spectral compositions of the Doppler-broadened resonance scattering and fluorescence are analyzed. It is shown that in these cases the Doppler line width is anisotropic. 
T. Ya. Popova, A. K. Popov, S. G. Rautian, and A. A. Feoktistov