Abstract

We consider the laser cooling scheme suggested by Shahriar et al.¹, which employs both ‘dark state’ and ‘polarisation gradient’ cooling mechanisms. In this scheme two counter propagating linearly polarised laser beams interact with a j = 1 to j = 1 atomic transition. A collection of atoms cooled in this manner will achieve a steady state momentum distribution even in the presence of an external force applied along the laser beams. This is because polarisation gradient cooling acts in a manner similar to a friction force. The magnitude of the applied force is reflected in the steady stale fluorescence from the cooled atoms, since the force, by continuously changing the atomic momentum, effectively produces a transition rate out of the dark state to states which fluoresce. We investigate the dependence of the steady stale fluorescence on the applied force. We: also calculate the effect that the force has on the steady state momentum distribution. 'Phis gives information about the limits to cooling imposed by stray forces, and the steady state net transport of atoms through the optical ‘lattice’.

© 1996 IEEE