Formation of cold Cs[sub 2] molecules through photoassociation

Abstract

In contrast to atoms, laser cooling of molecules is very difficult because of the lack of a closed two-level scheme for recycling the population. The molecular photoassociation of cold atoms, where two free atoms resonantly absorb one photon and form an excited molecule in a ro-vibrational state, has opened the way to the observation of long range dimers and to the determination of long range potential curves. The formation of translationally cold ground state molecules after spontaneous de-excitation of photoassociated molecules is thought to be an easier way than the laser cooling method applied to molecules, but unfortunately this process is mostly quenched by spontaneous emission that leads back to the dissociation of the transient molecule into two free atoms. The cesium atom is however a good candidate for the observation of translationally cold ground state molecules [1]. The and potentials below the dissociation limit + present Condon points at intermediate distances, which are responsible for the existence of rather efficient channels for the creation of triplet and singlet ground state molecules, respectively, by spontaneous emission. We present the first evidence for translationally cold molecules created after photoassociation in a vapor-cell magneto-optical trap. We have observed the fall of the cold molecular sample and we have measured its temperature, 300 K, which is of the same order as that of the initial cold atomic sample.

Formation of ultracold LiCs molecules

“…These are formed out of an ultracold gas of Li and Cs atoms in two spatially overlapped magneto-optical traps (MOTs). As observed in several experiments, homonuclear [24,25,26] and heteronuclear [22,23] alkali dimers can be formed 'directly' in the MOT, i.e., without applying a dedicated photoassociation laser. The molecule formation is generally attributed to photoassociation induced by the trapping laser light [27]; three-body recombination has also been conjectured as a possible cause for ultracold molecule formation in a MOT [24].…”

Editorial: Quo vadis, cold molecules?

“…The first stable ultracold molecules that were formed, detected by photoionization and time-of-flight selection of the molecular ions, were homonuclear alkali dimers [37][38][39][40][41][42][43]. Several mechanisms were identified as the stabilization step, all associated with specific properties of the potential curves in the excited electronic state.…”

Cold molecules: a chemistry kitchen for physicists?

“…This kind of heating process can be turned into an internal cooling process by choosing the right ingredients, in order to enhance the decay of photoassociated molecules into ultracold long-lived molecules. In 1997, the Orsay group observed for the first time such molecules starting from ultracold caesium atoms [24], thanks to both the peculiar properties of caesium dimers, and to the detection method.…”