Deceleration techniques for loading molecular MOTs
For almost two decades ultracold molecules have been on the cusp of realizing their potential for performing precision tests of fundamental physics and studying strongly interacting quantum systems. The realization that certain molecular species exhibit quasi-cycling transitions and can therefore be directly laser cooled has opened a new experimental pathway to producing molecular samples that are cold and dense enough to finally realize this potential. There is particular interest in the creation of molecular magneto-optical traps (MOTs) as starting points for more advanced investigations or as interesting systems in their own right. Currently, all molecular MOT experiments begin with a relatively fast (50-200 m/s) buffer-gas molecular beam. A primary experimental requirement is efficient deceleration to within the MOT capture velocity, typically 10 m/s or so. In the first half of this talk we will discuss our recent progress in producing samples of CaF, a prototypical laser-cooling candidate, for MOT loading. Results for direct laser slowing using both chirped narrow-band and broad-band "white-light" laser light will be presented and compared. Due to its particularly diagonal Frank-Condon factors, CaF is a nearly ideal laser-cooling candidate with a low reliance on repump lasers. Even so, slowing is accompanied by significant loss mechanisms, including transverse heating and increased beam divergence. Here we will present experimental methods aimed at countering these loss mechanisms.
The second half of the talk will be dedicated to an alternative slowing method, deemed Zeeman-Sisyphus deceleration. This approach uses optical pumping in the presence of static magnetic fields to achieve slowing and is particularly designed for decelerating buffer-gas beams consisting of molecules with less than ideal Frank-Condon factors. An additional benefit is the presence of net transverse guiding during the deceleration process, which acts to minimize the loss mechanisms present in direct laser cooling.