Towards an ultradeep dipole trap for molecules

Ultra-high continuous-wave intensities (>300 GW/cm²) in high-power, high-NA optical cavities enable applications from phase-contrast electron microscopy to proposed deep dipole traps for molecules. However, the intensity can be limited by the parametric oscillatory instability (PI), where light from a cavity mode is scattered by mirror vibrations into another mode. We observe PI in a 100-mm-long Fabry-Perot cavity, and show that the mechanical modes are bulk acoustic waves resonating inside the ULE mirrors. We measure the Q factor of ULE at MHz frequencies, and achieve >300 GW/cm² intensities by instead using low-Q Zerodur mirrors. This high-intensity cavity forms the basis of a new experiment [1] aimed at trapping small, chemically stable molecules in a buffer-gas loaded, deep optical trap for molecules. With a combined apparatus using our demonstrated laser inside a cryogenic system to buffer gas cool the molecules, we aim to demonstrate deep trapping of small chemically stable molecules like N₂, CO, O₂, and HCl, which we believe will open new possibilities in molecular spectroscopy, studies of cold chemical reactions, and precision measurement, amongst other fields of physics.