CM-AMO Seminar | Laser Cooling of a Diatomic Molecule

Speaker: Edward Shuman Faculty Candidate (Postdoctoral Fellow, Yale University)

The development of laser cooling techniques to produce ultracold (T < 1mK) atoms has lead to rapid advances in a wide array of fields.  Unfortunately, extending  laser cooling  to molecules has remained elusive.  The primary problem is that laser cooling requires a large number ( > 10⁴) of photon absorption/emission cycles.  Molecules, however, have vibrational and rotational degrees of freedom, which typically lead to high branching probabilities into a large number of unwanted sublevels.  Here we report on experiments demonstrating the laser cooling of a diatomic molecule which have overcome this problem.  We use the molecule strontium monofluoride (SrF) where only three lasers and a magnetic field are necessary to scatter > 10⁵ photons.  We have demonstrated 1-D transverse cooling of a beam of SrF, dominated by Doppler or Sisyphus-type cooling forces depending on experimental parameters. We observe a reduction in the velocity distribution by a factor of 3 or more, corresponding to final 1-D temperature T < 1 mK. This transverse cooling may be useful for a variety of experiments; in addition, our results open a path to trapping and 3D cooling of SrF to the ultracold regime.