Laboratoire Aimé Cotton, CNRS, Université Paris-Sud, Bât.505, 91405 Orsay, France.

Laser techniques applied to precision spectroscopy or to control of chemical reactions have improved considerably our knowledge on molecular physics. One of the greatest challenges of modern physical chemistry is to push forward the limits of electromagnetic or laser techniques to probe or to manipulate molecules at low temperatures where molecular interactions are dominated by pure quantum phenomena. In order to reach the sub-mK regime, we have developed since 1998 the photoassociation (PA) technique. Starting from cold atoms, PA associates them in molecular states by engineering a free-bound transition with a laser. The photoassociation methods rely on the spontaneous decay of the excited molecule toward a ground electronic state, enabling the creation of ultra-cold molecules in the micro-kelvin (translational) temperature range but in high vibrational levels.

In this poster, we shall present our results concerning a very general detection technique, based on broadband laser ionization, allowing the selection of the photoassociation transition presenting the highest formation rate of cold molecules. Following our pioneer work [1] we then present our recent development concerning the vibrational cooling of the formed molecules. We have considerably generalized the methods and we are now able to transfer several vibrational levels of Cs₂ molecules either from the singlet X¹Σ_g⁺ or from the triplet a³Σ_u⁺ states on demand into a single vibrational level (including v = 0) of the singlet X¹Σ_g⁺ ground electronic state. The technique is simply based on repeated optical pumping by laser light with a spectrum broad enough to excite all populated vibrational levels but frequency-limited in such a way to eliminate transitions from the desired level in which molecules accumulate. Limitations of the method as well as the possible extension to rotational cooling or to other systems will also be discussed.

[1] Optical pumping and vibrational cooling of molecules
M. Viteau, A. Chotia, M. Allegrini,N. Bouloufa, O. Dulieu, D. Comparat, P. Pillet Science 321 232 (2008)