Isotopologue-selective laser cooling of barium monofluoride molecules

Abstract

We demonstrate laser cooling of barium monofluoride (BaF) molecules, which are highly sought after for precision measurement applications. We synthesize time-sequenced optical spectra that can be precisely tailored to the hyperfine structure of this previously uncooled molecular species. Optimization of the optical spectra allows us to realize strong Sisyphus laser cooling forces that can efficiently collimate a molecular beam. Moreover, by carefully choosing the transitions involved in the cooling, we also demonstrate the first isotopologue-selective laser cooling of molecules, selectively addressing both the 138BaF and 136BaF isotopologues in the same molecular beam. Our results are an important step towards slowing and trapping of BaF molecules, and will also be useful for cooling other molecular species with complex level structure.