Buffer gas cooling of a continuous CO molecular beam

We characterize a continuous buffer gas cooled source using CO molecules. We show results about the source performance considering different parameters, like gas flow rate, nozzle size, and internal cell volume. The beam contains 2.5 × 1014 molecules/(s sr) at about 160 m/s. Moreover, for two rotational states we observe an unexpected population distribution that we tentatively attribute to a lower temperature inside the cell. Considering the importance of buffer-gas cooling for experiments on ultracold molecules prepared with direct laser cooling, we believe that our work will improve this key first-stage cooling, accelerating the adoption of molecules in the framework of quantum technologies.