Improved magneto-optical trapping of a diatomic molecule

TL;DR

This paper reports an improved magneto-optical trap for SrF molecules, achieving greater confinement and longer trap lifetime, advancing the goal of producing dense ultracold molecular gases through laser cooling.

Contribution

It introduces a new magneto-optical trapping scheme for SrF molecules that significantly enhances confinement and trap lifetime, building on atomic MOT techniques.

Findings

Radial spring constant increased 20-fold

Trap lifetime extended to 136 ms

Demonstrated further cooling of molecules

Abstract

We present experimental results from a new scheme for magneto-optically trapping strontium monofluoride (SrF) molecules, which provides increased confinement compared to our original work. The improved trap employs a new approach to magneto-optical trapping presented by M. Tarbutt, \emph{arXiv preprint} 1409.0244, which provided insight for the first time into the source of the restoring force in magneto-optical traps (MOTs) where the cycling transition includes dark Zeeman sublevels (known as type-II MOTs). We measure a radial spring constant $20\times$ greater than in our original work with SrF, comparable to the spring constants reported in atomic type-II MOTs. We achieve a trap lifetime $\tau_{\rm{MOT}}=136(2)$~ms, over $2\times$ longer than originally reported for SrF. Finally, we demonstrate further cooling of the trapped molecules by briefly increasing the trapping lasers' detunings. Our trapping scheme remains a straightforward extension of atomic techniques and marks a step towards the direct production of large, dense, ultracold molecular gases via laser cooling.