Towards laser cooling and trapping of aluminium monofluoride with high density

The aluminum monofluoride molecule (AlF) is an excellent candidate for laser cooling and magneto-optical trapping. All Q-lines of the A$^1\Pi,v'=0$ $\leftarrow$ X$^1\Sigma^+,v''=0$ band near 227.5 nm are rotationally closed and can be used for laser cooling. With a calculated Franck-Condon factor of 0.99992, each molecule can scatter on average 10$^4$ photons from a single laser. This corresponds to a velocity change of 382 m/s, sufficient to slow a cryogenic buffer gas or a supersonic molecular beam. AlF is a closed shell molecule with a binding energy of 7 eV and the A$^1\Pi, v=0$ state has a lifetime of 1.9 ns. This permits efficient production and slowing of the molecules and results in a large capture velocity of the magneto-optical trap ($>50$ m/s), an excellent basis to trap AlF molecules with high density. We present spectroscopic results necessary for laser cooling and trapping experiments. We determine the rotational and hyperfine energy levels in X$^1\Sigma^+, v=0$ and a$^3\Pi, v=0$ with kHz and in A$^1\Pi, v=0$ with MHz accuracy and infer precise spectroscopic constants for all three states. We determine the transition strengths between these states, measure their magnetic g-factors, their electric dipole moments and the lifetime of the A$^1\Pi,v=0$ state.