Atom-Molecule Collisions in an Optically Trapped Gas

Abstract

Cold inelastic collisions between confined cesium (Cs) atoms and Cs2 molecules are investigated inside a CO2 laser dipole trap. Inelastic atom-molecule collisions can be observed and measured with a rate coefficient of ∼ 2.5 × 10 −11 cm 3 s −1 , mainly independent of the molecular ro-vibrational state populated. Lifetimes of purely atomic and molecular samples are essentially limited by rest gas collisions. The pure molecular trap lifetime ranges 0,3-1 s, four times smaller than the atomic one, as is also observed in a pure magnetic trap. We give an estimation of the inelastic molecule-molecule collision rate to be ∼ 10 −11 cm 3 s −1 .

Observation of cold Rb2molecules trapped in an optical dipole trap using a laser-pulse-train technique

“…Recent experiments have observed atom-molecule cold collisions in mixed samples trapped in optical dipole traps [2,4]. In our case, we have verified that all the Rb 2 population decay curves, obtained at 0.9 mJ/pulse as a function of the atomic density, can be fitted by a single exponential.…”

“…We should also mention that it is surprising that we did not observe collisions between cold atoms and cold molecules, especially because our atomic density was about 10 times higher than the densities used in Refs. [2,4]. The main difference between the referenced experiments and ours is that our molecules were formed in high-lying vibrational states due to the near resonant light photoassociation.…”

“…After their formation, such molecules can be trapped in an optical dipole trap, since the trapping mechanism does not depend on molecular levels. Depending on the temperature, the molecular sample can be either in a thermal regime [2][3][4][5][6] or quantum regime [7][8][9]. Furthermore, they can be either in a single vibrational state [7][8][9] or in a mixture of states [2][3][4][5][6].…”

“…This technique has allowed a great development in the field of cold molecules. So far it has been applied using a single laser pulse for each molecular sample, and therefore it requires the preparation of a new molecular sample for each laser pulse [2][3][4][5][6]11]. In order to obtain reliable data, time-consuming averaging of a larger number of measurements over several different molecular samples is required.…”

“…In both cases, the time evolution of the molecule population allows one to obtain information on atom-molecule and molecule-molecule cold collisions. Therefore, the detection of such molecules is a key factor in all experiments, and it has been done either through the absorption imaging technique [7][8][9][10] or photoionization [2][3][4][5][6]11].…”