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.