Collective resonant Compton scattering by two-level particles

Abstract In this paper we provide a simple analytical demonstration that an unbunched beam of two-level particles coherently driven by a quasi-resonant counterpropagating field can give rise to coherent Compton back scattering due to self bunching which occurs via an instability very similar to that of a high gain Free Electron Laser. Since the initially weak scattering light is exponentially amplified and is Doppler upshifted in frequency, this effect constitutes the basic physical principle of a tunable source of coherent radiation: the Collective Atomic Recoil Laser (CARL). CARL extends the FEL bunching concept to any system of particles having two internal energy levels.