Doppler broadening and collision effects in a collective atomic recoil laser

We outline the basic physics of CARL in the cold and warm beam limits showing that recoil gain and self bunching can occur with very different features and intensities depending on the relevance of the velocity spread. In the cold beam limit we find the well known high gain FEL regime, whereas in the warm beam limit one has a small gain regime described by the derivative of the thermal velocity distribution.