Speaker
Description
Cryogenic buffer gas beams are the starting point for many cold molecule experiments, such as laser cooling and new precision tests of fundamental physics. However, the production of the species of interest in a molecular beam source is still poorly understood. We characterised molecular beams of AlF, CaF, MgF, and YbF molecules, produced via the chemical reaction of hot, laser-ablated metal atoms with a fluorine donor reactant gas and compared them to atomic beams of Ca, Al, and Yb in the same experimental setup. We conclude that the brightness of the AlF beam is comparable to a beam of laser-ablated Al atoms; the brightness of the molecular beams of CaF, MgF and YbF is significantly lower. The addition of either NF$_3$ or SF$_6$ to the buffer gas cell nearly extinguishes the Al beam, but has only a small effect on the Ca and Yb beams. The difference in reactivity is explained by the radical character of aluminium and the stability of the AlF molecule, while the other molecules are radicals that are formed from less reactive atoms.
Like CaF, YbF and AlF, MgF is a promising candidate for laser cooling and magneto-optical trapping experiments. However, the hyperfine-resolved spectroscopic information that was available when we first began measurements was insufficient to assess its potential. The main cooling cycle of MgF is the A$^2\Pi \leftarrow $X$^2\Sigma^+$ transition, which we investigated using hyperfine-resolved laser spectroscopy using a molecular beam from a cryogenic buffer-gas cell. Thus, we gained crucial information for future laser cooling experiments. We recorded 25 rotational transitions with an absolute accuracy of better than 20 MHz, assigned 56 hyperfine lines and determined precise rotational, fine and hyperfine structure parameters for the A$^2\Pi$ state. We found clear differences in MgF as compared with the group-II monofluorides CaF, SrF and BaF. The $\Lambda$-doubling is 100 times smaller and the hyperfine splitting of the excited states is strongly parity dependent. The radiative lifetime of the A$^2\Pi$ state was determined to be 7.2(3) ns, in good agreement with ab initio calculations. We determined the permanent electric dipole moments of $^{24}$MgF in its ground X$^2\Sigma^+$ and first excited A$^2\Pi$ states by measuring the Stark effect of selected rotational lines of the A$^2\Pi \leftarrow $X$^2\Sigma^+$ transition in electric fields of up to 10.6 kV cm$^{-1}$. Based on these measurements, we caution for potential losses from the optical cycling transition, due to electric field induced parity mixing in the excited state.
| Abstract Number (department-wise) | MP 13 |
|---|---|
| Department | MP (Meijer) |
