Theoretical And Experimental Studies On Electrostatic Stark Deceleration And Manipulation For Cold Molecules

As a novel subject, researches on cold molecules usually focus on cooling, trapping, quantum manipulation, and their applications, which are very interesting. It originated from the molecular beam experiments. As the development of science and technology, it becomes an interdisciplinary, involving electromagnetism, optics, quantum mechanics, and so on. And it has a plenty of applications, such as precision measurement of fundamental constants, molecular optics, spectroscopy of cold molecules, molecular clock, molecular chip, cold chemistry, and quantum calculation based on molecules. In this thesis, we focus on the experimental and theoretical researches of preparing cold neutral polar molecules using Stark deceleration, electrostatic guiding and trapping of cold molecules.First, we have demonstrated a controllable, highly efficient electrostatic surface guiding scheme for a supersonic ND3molecular beam, and studied the process both experimentally and theoretically. We find that the guiding center position and the relative molecule number can be easily controlled by changing the guiding voltages. When U1=17.3kV, and U2=20kV, a supersonic ND3molecular beam in the|JK>=|11> state (|JK>=|22>state) can be efficiently guided in our single charged wire scheme, and a transmission efficiency of higher than50%can be obtained. With the increase of guiding voltages, the acceptance of the guided cold molecules in2D position space will be slowly reduced, while the acceptance in2D velocity space will be rapidly increased. In addition, comparing with our previous two-wire scheme, the guiding center position of our present single wire scheme can be easily adjusted by controlling the guiding voltages, facilitating alignment in the vacuum chamber, and our single wire scheme has a higher transmission efficiency than our previous two-wire scheme when the guiding voltage Uwire is higher than10.4kV.Then we construct the second generation Stark decelerator in our lab. The new decelerator is improved in many parts, comparing to the first one. In the insulating parts, the creepage distance is increased, and higher voltages can be applied to the electrodes; The pulse valve is pre-cooled with liquid nitrogen cooling system, which means that the velocity of molecular beam can be reduced; In addition, it has a total of180pairs of deceleration stages, which can slow down new kinds of molecules with smaller dipole moments. In the experiment, we test the ability of our decelerator using ND3molecules as a sample. A molecular packet of71m/s can be obtained, when a low voltage of±6kV is applied to the electrodes, and a synchronous phase of45±is used. If the voltage increases to±12kV, the340m/s beam can be decelerated to-50m/s. We also propose an electrostatic trap for cold polar molecules using two hemispherical electrodes. Simulation results show that the loading efficiency can be higher than90%, and molecules in the trap can be cooled adiabatically from8.8mK(Tx(y>) and7.7mK(Tz) to3.0mK and1.9mK, respectively.Next, we theoretically study whether D2O molecules can be slowed efficiently using our new Stark decelerator, and find that D2O molecules in|1,1,1> state can be decelerated to71m/s when voltages on electrodes are±20kV, with an initial velocity of300m/s, and a synchronous phase of55±. In order to verify the feasibility of electrostatic trapping of D2O molecules, we precool the pulse valve, and reduce the initial beam velocity to300m/s as well as the slow voltages to18kV. The simulated results show that a D2O wave packet can be decelerated to lOm/s, when the synchronous phase is64.6°. Then we simulate the loading process of the electrostatic trapping for D2O molecules, and find that a loading efficiency for D2O of40%can be obtained, if the conditions are optimized.Finally, we have proposed a molecular chip to create a single trap, a ID and a2D electrostatic lattice which is suitable for confining cold and ultracold molecules or even quantum degenerate gases prepared in WFS states. We calculate the electric field distribution of a square coil and a grounded metal plate and compare it to the one simulated by finite element software to verify the accuracy. We optimize the switching moment to reach a high loading efficiency for different incident beam speed by Monte Carlo simulations, and for a beam speed vz=15m/s, we have a loading efficiency of17.7%for the whole2D lattice. We also discuss the compensation of the edge field effect of the electrostatic lattice. In addition, we proposed a more open lattice structure, which obtains a loading efficiency of9.2%and has higher trapping centers.