Cold cesium molecules: from formation to cooling

Abstract

Recent experiments on formation of translationally cold ground state molecules, their subsequent broadband vibrational cooling and study of rotations are presented together with the related modeling. We produce cold molecules by photoassociating pairs of cold cesium atoms that can decay into ground state molecules in different vibrational levels. Then we laser cool the vibrational degree of freedom by selecting a single target vibrational level. Our method is based on repeated optical pumping by laser light with a spectrum broad enough to excite all populated vibrational levels but limited in its frequency bandwidth with a spatial light modulator. In such a way we are able to eliminate transitions from the selected level, in which molecules accumulate. Results for vibrational cooling into the v = 0, v = 1, v = 2 and v = 7 level of the singlet X ¹Σ _g ground electronic state are presented. Depletion spectroscopy is performed to study the rotational distribution of the created molecules. In the theoretical modeling of the process we are able to reproduce our results and investigate the prospects for a ‘complete’ cooling of molecules, including also their rotational degree of freedom.

Keywords:

• cold molecules
• optical pumping
• vibrational cooling
• laser cooling

Acknowledgements

Fundamental work on earlier experiments and on their theoretical interpretation by Matthieu Viteau, Amodsen Chotia, Nadia Bouloufa and Olivier Dulieu are gratefully acknowledged. This work is supported by the ‘Institut Francilien de Recherche sur les Atomes Froids’ (IFRAF) and (in Toulouse) by the Agence Nationale de la Recherche (Contract ANR–06-BLAN-0004) and the Del Duca foundation. M.A. thanks the EC-Network EMALI and the “Université Franco-Italienne” (Galileo Project). A.F. thanks the RTRA ‘Triangle de la Physique’ for support.