Superradiant light scattering and grating formation in cold atomic vapours

A semi-classical theory of coherent light scattering from an elongated samp le of cold atoms exposed to an off-resonant laser beam is presented. The mo del, which is a direct extension of that of the collective atomic recoil la ser, describes the emission of two superradiant pulses along the sample's m ajor axis simultaneous with the formation of a bidimensional atomic grating inside the sample. It provides a simple physical picture of the recent obs ervation of collective light scattering from a Bose-Einstein condensate [Sc ience 285 (1999) 571]. In addition, the model provides an analytical descri ption of the temporal evolution of the scattered light intensity which show s good quantitative agreement with the experimental results of Inouye et al . (C) 2001 Elsevier Science B.V. All rights reserved.