  We extend the Collective Atomic Recoil Lasing (CARL) model including the
effects of friction and diffusion forces acting on the atoms due to the
presence of optical molasses fields. The results from this model are consistent
with those from a recent experiment by Kruse et al. [Phys. Rev. Lett. 91,
183601 (2003)]. In particular, we obtain a threshold condition above which
collective backscattering occurs. Using a nonlinear analysis we show that the
backscattered field and the bunching evolve to a steady-state, in contrast to
the non-stationary behaviour of the standard CARL model. For a proper choice of
the parameters, this steady-state can be superfluorescent.
