ANISOTROPIC VELOCITY-DEPENDENT VORTEX FORCES - 2-LEVEL ATOMS IN 2-DIMENSIONAL STANDING WAVES

We consider the velocity-dependent light pressure force on a two-level atom interacting with a two-dimensional nearly resonant standing-wave light field. We show that there can be anisotropic cooling-heating fo rces that will cool the atoms along one field axis while heating them along the perpendicular axis. The force is identified as a spontaneous vortex force associated with the local traveling wave character of th e two-dimensional field. We provide a simple interpretation of this an omalous force in terms of the interplay between the vortical momentum now of the light field and a motion-induced population transfer betwee n the ground and excited atomic states.