Magneto-Optical Trapping of Aluminum Monofluoride

Magneto-optical trapping of molecules has thus far been restricted to molecules with ^{2}Σ electronic ground states. These species are chemically reactive and only support a simple laser cooling scheme from their first excited rotational level. Here, we demonstrate a magneto-optical trap (MOT) of aluminum monofluoride (AlF), a deeply bound and intrinsically stable diatomic molecule with a ^{1}Σ^{+} electronic ground state. The MOT operates on the strong A^{1}Π←X^{1}Σ^{+} transition near 227.5 nm, whose Q(J) lines are all rotationally closed. We demonstrate a MOT of about 6×10^{4} molecules for the J=1 level of AlF, more than 10^{4} molecules for J=2 and 3, and with no fundamental limit in going to higher rotational levels. Laser cooling and trapping of AlF is conceptually similar to the introduction of alkaline-earth atoms into cold atom physics, and is key to leveraging its spin-forbidden a^{3}Π←X^{1}Σ^{+} transition for precision spectroscopy and narrow-line cooling.