Interactions of lithium and cesium in an optical dipole trap

The thermodynamics in a mixture of two different atomic gases at ultralow temperatures are explored. An intrinsically loss-free approach is presented which can be generalized to a vast range of atomic species and even molecules. The model system is a mixture of cesium and lithium in an extremely far-detuned optical dipole trap. Cesium is an excellent cooling agent, since it can be optically cooled to very low temperatures, mainly due to its high mass. Lithium, on the other side, is difficult to cool optically. In addition, it is nearly an ideal gas due the very small cross-section for elastic Li-Li collisions. Thermalization of Li thus occurs purely through collisions with the Cs atoms. From the time scale of thermalization one can deduce the a priori unknown interspecies scattering cross-section. Currently, the formation of ultracold Cs/sub 2/ molecules through photoassociation in the dipole trap is being investigated. The production of molecules in the lowest vibrational states of the outer well of the O/sub g//sup -/ potential is possible to observe by investigating the trap loss signals. Phenomena like saturation effects can be studied.