Theory of an optical dipole trap for cold atoms - art. no. 043406

The theory of an atom dipole trap composed of a focused, far red-detuned, t rapping laser beam, and a pair of red-detuned, counterpropagating, cooling beams is developed for the simplest realistic multilevel dipole interaction scheme based on a model of a (3+5)-level atom. The description of atomic m otion in the trap is based on the quantum kinetic equations for the atomic density matrix and the reduced quasiclassical kinetic equation for atomic d istribution function, ft is shown that when the detuning of the trapping fi eld is much larger than the detuning of the cooling field, and with low sat uration, the one-photon absorption (emission) processes responsible for the trapping potential can be well separated from the two-photon processes res ponsible for sub-Doppler cooling atoms in the trap. Two conditions are deri ved that are necessary and sufficient for stable atomic trapping. The condi tions show that stable atomic trapping in the optical dipole trap can be ac hieved when the trapping field has no effect on the two-photon cooling proc ess and when the cooling field does not change the structure of the trappin g potential but changes only the numerical value of the trapping potential well. It is concluded that the separation of the trapping and cooling prece sses in a pure optical dipole trap allows one to cool trapped atoms down to a minimum temperature close to the recoil temperature, keeping simultaneou sly a deep potential well.