Cryogenic Buffer Gas beams of AlF, CaF, MgF, YbF, Al, Ca, Yb and NO -- a comparison

TL;DR

This study compares cryogenic buffer gas beams of various molecules, revealing differences in brightness, reaction efficiency, and stability, with implications for cold molecule experiments.

Contribution

It provides a direct comparison of molecular beam brightness and reaction dynamics for AlF, CaF, MgF, YbF, and NO, highlighting the effects of different reactants and conditions.

Findings

AlF beam brightness is comparable to atomic beams.

CaF, MgF, YbF beams are significantly dimmer than AlF.

NF$_3$ enhances molecule production efficiency.

Abstract

Cryogenic buffer gas beams are central to many cold molecule experiments. Here, we use absorption and fluorescence spectroscopy to directly compare molecular beams of AlF, CaF, MgF, and YbF molecules, produced by chemical reaction of laser ablated atoms with fluorine rich reagents. The beam brightness for AlF is measured as $2\times 10^{12}$ molecules per steradian per pulse in a single rotational state, comparable to an Al atomic beam produced in the same setup. The CaF, MgF and YbF beams show an order of magnitude lower brightness than AlF, and far below the brightness of Ca and Yb beams. The addition of either NF$_3$ or SF$_6$ to the cell extinguishes the Al atomic beam, but has a minimal effect on the Ca and Yb beams. NF$_3$ reacts more efficiently than SF$_6$, as a significantly lower flow rate is required to maximise the molecule production, which is particularly beneficial for long-term stability of the AlF beam. We use NO as a proxy for the reactant gas as it can be optically detected. We demonstrate that a cold, rotationally pure NO beam can be generated by laser desorption, thereby gaining insight into the dynamics of the reactant gas inside the buffer gas cell.