Abstract

The manipulation of atomic motion by resonant and near-resonant interaction with optical fields is the subject of intense current interest. Until now experimental attention has focused on the regime of linear atom-light interactions where the atomic dynamics are driven by externally specified optical fields. As has been discussed theoretically by several groups[1], dipole-dipole interactions lead to a light mediated nonlinearity in ultracold atomic beams. The nonlinearity results in a cubic nonlinear Schrödinger equation for the atomic evolution, and suggests the possibility of observing atomic self-focusing and solitons. I present coupled equations[2] that describe the joint evolution of the matter and optical waves. Including the effects of diffraction, and nonlinearity, in the evolution of both the optical and atomic fields leads to new physical phenomena. Dipole forces, being proportional to ∇|A|², where A is the envelope of the optical field, occur only in spatially inhomogeneous fields. However, spatial gradients grow on an initially homogeneous background due to modulational instability under conditions of nonlinear self-focusing. The spatial gradients lead to dipole forces and thus, the atomic motion may be subject to forces nonlinear in the atomic density, even in the limit of a thermal atomic beam with short coherence length. Numerical results demonstrate filamentation of the atomic beam, also in the limit of low atomic phase space density. In addition, an exact solution is found describing the possibility of self-trapped propagation of both the optical and atomic fields.

© 1998 IEEE