PROPAGATION EFFECTS IN A COLLECTIVE ATOMIC RECOIL LASER

We present a theoretical investigation of propagation effects in a col lective atomic recoil laser (CARL) operating in the FEL limit. We cons ider the cases where the system evolves while in free space and while enclosed in a ring cavity. in the case where no cavity is present, we show that the scattered radiation consists of soliton-like superfluore scent pulses. in the case of a 'good' cavity we arrive analytically at a condition to neglect propagation effects. This condition implies th at in order to use the so-called mean field approximation, the conditi on (Lambda root L)/l(c)(3/2)-->0, T-->0 must be satisfied with (Tl-c)/ (Lambda root L)(2/3) finite where I-c is the cooperation length of the system, T is the transmission coefficient of the mirrors. L and ii ar e the sample length and cavity length respectively. We confirm the val idity of this condition using a numerical analysis and provide a simpl e physical interpretation. In the mean field limit, we show that if th e cavity Linewidth is greater than the spectral width of the pulse emi tted by the sample, the emission remains superfluorescent and is not s ensitive to the presence of the cavity. We also show that in the oppos ite case the emission is sensitive to the cavity parameters and no lon ger superfluorescent.