Theoretical And Experimental Study On ND₃via Stark Deceleration And Surface Manipulation

The technique of electrostatic Stark deceleration has played an important role in production of translational cold polar molecules since its first experimental realization in1999, yielding a variety of cold polar molecules. In this thesis we give a detailed description of the experiments with our homemade Stark decelerator. Using the decelerator, a supersonic ND3beam is successfully decelerated from330m/s to24m/s, with a translational temperature of-36mK in the moving frame. Relationships between the performance of the decelerator and various parameters, including the kinetic energy loss per stage versus the synchronous phase angle φ0, the final central velocity of slowed molecular packet versus both the phase angle φ0and the deceleration stage number, and the relative slowing efficiency versus the phase angle φ0, are studied both theoretically and experimentally. In addition, we propose and study a new mode to operate a Stark decelerator that allows preparing a slow, number density enhanced, high-energy-resolution molecular beam (8mK).Inspired by the great achievements in the field of atom chips and their fundamental applications in Bose-Einstein condensation, matter wave interferometry and free fall experiments, researchers currently begin to pursue molecule chips that promise more exciting prospects, such as the realization of quantum computation that employs cold polar molecules as quibits. In the fourth chapter we propose a scheme of surface electrostatic velocity filter capable of preparing cold polar molecules on the surface of a substrate by selecting low-velocity component of an effusive beam from a thermal gas reservoir. Using ND3as a molecular sample, the dependence of the performance of the filter on the parameters of both the filter setup and the incident molecular beam is investigated by using a theoretical model and Monte Carlo simulations. A detailed study of the guiding process of molecules, including the evolution of phase space density of the packet in the filter, is carried out and shows that the beam selection process is mainly completed in the front part of the filter.A slow beam produced by an electrostatic velocity filter always holds a wide velocity spread, unfavorable for some cold collision studies. In this paper we propose a scheme of surface buncher, composed by an array of electrodes, which permits to longitudinally focus the resulting beam from the electric velocity filter. By exploiting the interaction of molecules with time-varying inhomogeneous electric fields, the velocity distribution of the ensemble of the molecules is compressed and then a cold, slow molecular beam is prepared in vicinity of a substrate. In addition, we propose a scheme of continuously loadable storage ring that allows continuously loading molecular beams or simultaneously storing a large number of pulsed molecular packets, with high loading efficiency. The possibility of our scheme combining electrostatic velocity filter, buncher and storage ring is shown by means of particle trajectory simulations.In addition, the process of design and development of the experimental apparatus for surface manipulation is given in the fifth chapter, including the design and assembly of both the vacuum chamber and experimental components. The development of computer program package for our experiment is introduced as well. Finally, the conclusions and outlook are presented in the final chapter.