Combining high intensity cavities with cryogenic buffer-gas cells for deep dipole trapping of molecules

Despite much interest in studying cold molecules, access to cold, trapped molecules has been limited to only a small class of species. We aim to expand trapping techniques to include a variety of small, chemically stable molecules, such as N₂, CO, O₂, and HCl [1]. To this end, we present here a unique experimental apparatus, which has produced 1064-nm laser intensities over 400 GW/cm² in a region between two opposing cryogenic buffer gas cells that can be cooled to 1.5 K. The laser, produced in a tightly-focused buildup cavity, forms a far-off-resonant dipole trapping potential, with a trap depth of ∼10 K. The buffer-gas cells are therefore cold enough to directly load molecules into the trap. Since both buffer-gas cooling and the very far-off-resonant trapping mechanism are insensitive to a molecule’s energy level structure and dipole moments, multiple species can be trapped at the same time. Detection of buffer-gas-loaded molecules in our trap via resonantly-enhanced multiphoton ionization will represent the first observation of molecules in our targeted class trapped in their internal ground states. We hope to successfully demonstrate trapping very soon, which will open new possibilities in molecular spectroscopy, studies of cold chemical reactions, and precision measurement, amongst other fields of physics.

[1] Ashwin Singh et al., Dynamics of a buffer-gas-loaded, deep optical trap for molecules. Phys. Rev. Research 5, 033008 – Published 5 July 2023