RELATIVISTIC THEORY OF THE COLLECTIVE ATOMIC RECOIL LASER

We propose a new method for producing coherent, tunable radiation at s hort wavelength using the collective Compton backscattering of a count er-propagating radiation field from a relativistic two-level particle beam (generically called atoms). Under proper conditions one can have exponential growth of the co-propagating, back-scattered radiation at the Doppler up-shifted frequency at the expense of the recoil energy o f the particle beam. This growth arises from self-bunching of the part icle beam which generates the coherent back scattering of the incident field. We show that the gain and efficiency of the system, for a give n density, scale as the inverse cube root of the beam energy instead o f the inverse of the energy as in the free electron laser (FEL). Examp les of an ion beam and of electric spins are discussed.