Optical cycling of AlF molecules

Abstract

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 $A^1\Pi \leftrightarrow X^1{\Sigma }^{+}$ transition. We measure the brightness of the molecular beam to be $>10^{12}$ 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 $17(2)\times 10^6$ 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 $8.7(1.5)\times 10^5$ m/s${}^2$. We demonstrate that losses from the optical cycle due to vibrational branching to $X^1{\Sigma }^{+},v^{\prime \prime }=1$ 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.

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• Collisional losses of ultracold molecules due to intermediate complex formation
• Laser spectroscopy of aromatic molecules with optical cycling centers: strontium (I) phenoxides
• Influence of source parameters on the longitudinal phase-space distribution of a pulsed cryogenic beam of barium fluoride molecules
• Multivalent optical cycling centers in polyatomic molecules
• Magneto-optical trapping of aluminum monofluoride
• Spectroscopic characterization of the a${}^3\Pi$ state of aluminum monofluoride
• The chemistry of AlF and CaF production in buffer gas sources
• Laser cooling of molecules
• Nuclear spin relaxation in cold atom-molecule collisions
• Molecular dynamics-driven global tetra-atomic potential energy surfaces: Application to the AlF dimer
• Hyperfine structure of the ${\mathbf{A}}^1\mathbf{\Pi }$ state of AlCl and its relevance to laser cooling and trapping
• Spectroscopic characterization of singlet-triplet doorway states of aluminum monofluoride
• Dynamics of translational and rotational thermalization of AlF molecules via collisions with cryogenic helium
• DiPolMol-Py: A Python package for calculations for ${}^2\Sigma$ ground-state molecules
• Low Duty Cycle Pulsed UV Technique for Spectroscopy of Aluminum Monochloride
• Interactions and cold collisions of AlF in the ground and excited electronic states with He
• A stable 2 W continuous-wave 261.5 nm laser for cooling and trapping aluminum monochloride
• Highly spin-polarized molecules via collisional microwave pumping