News
Progress on Laser Cooling of CaF
The internal structure and the long-range dipole-dipole interactions of ultracold polar molecules open new avenues in studying physics such as the quantum simulation of strongly correlated Hamiltonians, ultracold controlled chemistry or precision measurements. At present, a reliable general method to produce an ultracold sample of molecules is desired, but not available. The goal of this experiment is to laser cool CaF molecules and load a 3D magneto-optical trap (MOT) with CaF. While traditional laser cooling relies on the scattering of many photons, cooling is impeded in the case of molecules due to their complex level structure leading to population of dark states (rotational and vibrational) after just a few scattering events. Starting from a cryogenic buffer-gas cell which produces a molecular beam with a peak forward velocity of ca. 65 m/s with ca. 109 molecules per pulse, we plan to employ additional repumping lasers to address the dark state population to bring the molecule back into the cooling cycle. At present, we successfully demonstrated photon cycling with the first repumping beam which addresses the first excited vibrational (dark) state (see Fig. 1). With a total of two repumpers, our scheme will allow for the scattering of ca. 100000 photons which is sufficient to stop the CaF beam. A part of this photon budget will be used to slow the molecule beam below the MOT capture velocity which is estimated to be < 20 m/s and trap CaF in a 3D MOT.