Atomic self-trapping and self-focusing in a light medium

Light-induced dipole-dipole interactions in a coherent atomic field result in an effective nonlinear interaction between atoms. This nonlinearity can induce self-focusing and self-trapping of a coherent atomic beam undergoing propagation through a travelling-wave laser beam; we show how such a scheme could be realised and evaluate the critical density required for atomic self-focusing and self-trapping. An analogy to optical self-focusing and self-trapping is discussed.