Abstract

The many laser cooling schemes that exist, provide various amounts of force for different velocity ranges. We have analyzed a new method that is similar to the familiar dipole-force method for a two-level atom but that involves a third, reservoin level. This method offers several improvements over the dipole-force method, at the cost of a more complicated system. Similar cooling schemes have recently been proposed in the literature,^1,2 We consider an atomic system consisting of three levels: an exited state |a〉 that decays to two stable ground states |g〉 and |r〉, The |e〉-to-|g〉 transition is driven by an intense standing wave, as in the usual dipole-force scheme, whereas the |r〉-to-|e) transition is driven by a single traveling wave of moderate intensity. By finding the steady-state density matrix, we are able to exactly calculate the force experienced by an atom moving in these fields. A characteristic force-versus-velocity plot is shown in Fig. 1. The variable parameters of the model are the intensities and frequencies of the two laser fields and the branching ratio for the excited-state decay.

© 1993 Optical Society of America