Spectrum of coherently backscattered light from two atoms
  We present a detailed analytical and numerical analysis of the inelastic coherent backscattering spectrum of laser light incident on cold atoms. We identify frequency domains where the interference contribution can be positive \emph{as well as} negative -- or exhibits dispersive character. These distinctive features are explained by reciprocity arguments and dressed state two-photon scattering amplitudes. 
Vyacheslav Shatokhin, Thomas Wellens, Beno\^it Gr\'emaud, Andreas   Buchleitner