Molecular Laser Cooling in a Dynamically Tunable Repulsive Optical Trap

Recent work with laser-cooled molecules in attractive optical traps has shown that the differential ac Stark shifts arising from the trap light itself can become problematic, limiting collisional shielding efficiencies, rotational coherence times, and laser-cooling temperatures. In this Letter, we explore trapping and laser cooling of CaF molecules in a ring-shaped repulsive optical trap. The observed dependences of loss rates on temperature and barrier height show characteristic behavior of repulsive traps and indicate strongly suppressed average ac Stark shifts. Within the trap, we find that Lambda-enhanced gray molasses cooling is effective, producing similar minimum temperatures as those obtained in free space. By combining in-trap laser cooling with dynamical reshaping of the trap, we also present a method that allows highly efficient and rapid transfer from molecular magneto-optical traps into conventional attractive optical traps, which has been an outstanding challenge for experiments to date. Notably, our method could allow nearly lossless transfer over millisecond timescales.

Automated summary

Recent work has shown that the differential ac Stark shifts resulting from the trap light itself can pose problems in laser-cooled molecules in attractive optical traps. This Letter investigates trapping and laser cooling of CaF molecules in a ring-shaped repulsive optical trap. The results demonstrate that Lambda-enhanced gray molasses cooling is effective within the trap, and a method is proposed for efficient transfer from molecular magneto-optical traps into conventional attractive optical traps.