Towards hybrid trapping of cold molecules and cold molecular ions

Abstract

A pinhole discharge unit as well as a dielectric barrier discharge (DBD) head were developed for the Nijmegen pulsed valve (NPV) and the molecular beam properties accessible from each source were characterised and compared. The discharge conditions were optimised for maximum hydroxyl radical density. It was found that the DBD source yields colder OH radicals, whereas the pinhole discharge source provides a threefold larger radical density compared to the DBD discharge head. Translationally cold packages of hydroxyl radicals (Ttrans > 1mK) were produced by means of Stark deceleration and a 124-stage Stark decelerator was set up in the laboratory. The decelerator was conditioned, characterised and optimised for operation at low final velocities (v < 40 m/s). The performance of the decelerator was assessed by determining the density of OH radicals available after the deceleration process. In a final step, a translationally cold OH package was loaded into a cryogenic magnetic trap. The trap design, the coupling of the magnetic trap to the Stark decelerator and the loading efficiency were numerically optimised employing a direct search algorithm on Monte-Carlo trajectory simulations. The cryogenic environment efficiently prevents black-body radiation from pumping OH radicals out of trappable states and the background pressure improved significantly. Under cryogenic conditions the 1/e trap lifetime improved by a factor of 30 compared to room temperature. The magnetic trap forms part of a hybrid trapping scheme for neutral molecules and ionic species. This novel type of trap represents a versatile environment for investigating ion-neutral molecule reactions in the cold regime, while offering full control over the contributing quantum states.