Elastic vs. inelastic coherent backscattering of laser light by cold   atoms: a master equation treatment
  We give a detailed derivation of the master equation description of the coherent backscattering of laser light by cold atoms. In particular, our formalism accounts for the nonperturbative nonlinear response of the atoms when the injected intensity saturates the atomic transition. Explicit expressions are given for total and elastic backscattering intensities in the different polarization channels, for the simplest nontrivial multiple scattering scenario of intense laser light multiply scattering from two randomly placed atoms. 
Vyacheslav Shatokhin, Cord A. M\"uller, Andreas Buchleitner