# Buffer-gas cooling, high-resolution spectroscopy and optical cycling of barium monofluoride molecules

## TL;DR

This paper demonstrates buffer-gas cooling, high-resolution spectroscopy, and optical cycling of cold BaF molecules, achieving high flux, long-lived excited states, and conditions suitable for laser cooling of this heavy diatomic molecule.

## Contribution

It introduces a new method for producing cold BaF molecules with high flux and demonstrates a quasi-cycling transition suitable for laser cooling.

## Key findings

- Achieved a molecular beam flux of over 1e10 molecules/sr/pulse.
- Measured a longer-than-expected lifetime of the A'Delta state (~790 ns).
- Established conditions for laser cooling of BaF molecules.

## Abstract

We demonstrate buffer-gas cooling, high-resolution spectroscopy and cycling fluorescence of cold barium monofluoride (BaF) molecules. Our source produces an intense and internally cold molecular beam containing the different BaF isotopologues with a mean forward velocity of 190 m/s. For a well-collimated beam of 138BaF we observe a flux of more than 1e10 molecules/sr/pulse in the X2Sigma, N=1 state in our downstream detection region. Studying the absorption line strength of the intermediate A'Delta state we infer a lifetime of 790+\-346 ns, significantly longer than previously estimated. Finally, highly-diagonal Franck-Condon factors and magnetic remixing of dark states allow us to realize a quasi-cycling transition in 138BaF that is suitable for future laser cooling of this heavy diatomic molecule.