A conveyor-belt magneto-optical trap of CaF

Achieving high-density samples of laser-cooled molecules is a critical step toward advancing applications in precision measurements, ultracold chemistry and quantum science. We report the experimental realization of a high-density conveyor-belt magneto-optical trap for calcium monofluoride (CaF) molecules. The obtained highly-compressed cloud has a mean radius of 64(5) μm and a peak number density of 3.6(5) × 1010 cm−3, a 600-fold increase over the conventional red-detuned MOTs of CaF, and the densest molecular MOT observed to date. Subsequent loading of these molecules into an optical dipole trap yields up to 2.6 × 104 trapped molecules at a temperature of 14(2) μK with a peak phase-space density of ~ 2.4 × 10−6. This opens new possibilities for a range of applications utilizing high-density, optically trapped ultracold molecules. Magneto-optical traps (MOTs) are a workhorse for laser cooling of atoms and were recently extended to molecules. Yet, new mechanisms for molecular trapping and cooling are still an open area of exploration. Here, the authors show a blue-detuned MOT based on a conveyor-belt effect for CaF molecules, yielding higher number densities, comparable with some atomic MOTs.