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 Π ↔ X 1 Σ + 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) × 10 6 s −1 can be sustained using a single, fixed-frequency laser without the need to modulate the polarisation. The acceleration due to the radiation pressure force is measured by deflecting the molecular beam to 8.7(1.5) × 10 5 m/s 2 . We demonstrate that losses from the optical cycle due to vibrational branching to X 1 Σ + , 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.

Dynamics of translational and rotational thermalization of AlF molecules via collisions with cryogenic helium

“…Recently, we identified the aluminum monofluoride (AlF) molecule as a promising candidate for laser cooling. Its virtues include a large photon scattering rate and favorable Franck-Condon factors [57][58][59]. Moreover, we demonstrated that AlF molecules can be efficiently produced in a pulsed buffer-gas source, with a yield of > ∼ 10 12 molecules per steradian per pulse [58].…”

“…Its virtues include a large photon scattering rate and favorable Franck-Condon factors [57][58][59]. Moreover, we demonstrated that AlF molecules can be efficiently produced in a pulsed buffer-gas source, with a yield of > ∼ 10 12 molecules per steradian per pulse [58]. A high yield of cryogenically thermalized molecules is a key prerequisite for reaching quantum degeneracy in a cooling step that follows upon laser cooling, namely forced evaporation.…”

A laser cooling scheme for precision measurements using barium monofluoride (137Ba19F) molecules

“…We also expect them to be relevant for species with similar structure, like isotopologues of CaF, SrF or radioactive RaF [30] containing metal atoms with nonzero nuclear spin. Other examples where optical cycling and laser cooling of diatomic molecules with two nuclear spins have recently been considered include AlF [31], TlF [32] and YbOH [33], but detailed studies of laser cooling forces have so far been lacking. * t.langen@physik.uni-stuttgart.de Relevant energy levels for the laser cooling of 137 BaF including their relative energy shifts.…”