Photoassociation, cold molecules and prospects

Photoassociation of cold atoms opens a promising way for the obtention of dense samples of cold molecules. In a photoassociation process, two atoms absorb resonantly one photon to form a cold molecule in a ro-vibrational level of an electronically excited state. Unfortunately, for most of the considered configurations, molecules dissociate after spontaneous emission. Long-range states below the dissociation limits 6s+6p of the cesium dimer present several configurations with Condon points at intermediate distances, offering efficient channels for the formation of Cs₂ molecules in the ground state or in the lowest triplet state. Temperatures of the molecular cloud of 20 μK and formation rates of 0.1 cold molecule per second and per atom have been measured. The cold molecular sample is however prepared in several ro-vibrational levels. The possibility to stimulate the emission and to prepare all the molecules in a selected well-defined ro-vibrational level has been demonstrated. This stimulated Raman process opens the way to prepare cold molecules in all degrees of freedom (translation, vibration and rotation).