RADIATIVE COOLING FORCE IN ATOMS WITH MULTIPLET STRUCTURE

This paper extends the calculation of laser cooling forces on atoms wi th magnetic degeneracy to the case where the excited state is composed by a multiplet of levels with arbitrary energy separation. The sub-Do ppler force that arises in the sigma(+),sigma(-) field configuration i s found to be strongly affected if other atomic levels lie close to th e excited level of the cooling transition. The paper examines in detai l the case in which the excited multiplet comes from spin-orbit coupli ng of angular momentum L = 1 and spin S = 1, forming the J(e) = 0, J(e ) = 1, and J(e) = 2 energy levels. The cooling transition J(g) = 1 <-> J(e) = 2 shows the sub-Doppler structure due to magnetic degeneracy. The force is modified by the two other transitions (if sufficiently cl ose), even If these do not provide any mechanical effect on the atom w hen acting alone. The paper presents a detailed scheme for the constru ction of the relevant optical Bloch equations for the present case, wh ich can be generalized to treat more complex atomic structures. The so lutions to these equations are then discussed; several cases of energy separation are worked out and the ensuing graphs of the radiative for ce are shown. The calculations were carried out in both low-and strong -field regimes.