Optical Cycling of AlF Molecules

Aluminium monofluoride (AlF) is a promising candidate for laser cooling and trapping at high densities. We show efficient production of AlF in a bright, pulsed cryogenic buffer gas beam, and demonstrate rapid optical cycling on the Q rotational lines of the A¹Π↔X¹Σ⁺ transition. We measure the brightness of the molecular beam to be >10¹² molecules per steradian per pulse in a single rotational state and present a new method to determine its velocity distribution in a single shot. The photon scattering rate of the optical cycling scheme is measured using three different methods, and is compared to theoretical predictions of the optical Bloch equations and a simplified rate equation model. Despite the large number of Zeeman sublevels (up to 216 for the Q(4) transition) involved, a high scattering rate of at least 17(2)×10⁶ s⁻¹ can be sustained using a single, fixed-frequency laser without the need to modulate the polarisation. We deflect the molecular beam using the radiation pressure force and measure an acceleration of 8.7(1.5)×10⁵ m/s². We demonstrate that losses from the optical cycle due to vibrational branching to X¹Σ⁺,v''= 1 can be addressed efficiently with a single repump laser. Further, we investigate two other loss channels, parity mixing by stray electric fields and photo-ionisation. The upper bounds for these effects are sufficiently low to allow loading into a magneto optical trap.