Theoretical Researches On Surface Filtering,Bunching And Storing Of Polar Molecules

With the developments of cold molecules in the past two decades,remarkable achievements have been made,and a lot of very important applications can be used in many fields,such as physics,chemistry,and so on.Many approaches have been developed to produce and control molecules,such as electrostatic velocity filtering,Stark deceleration,Zeeman deceleration,buffer gas cooling,photoassciation,and so on.This paper mainly studies the production and control of cold molecules.A scheme of surface manipulation and control of polar molecules is proposed,which combines three tools of electrostatic velocity filtering,bunching and storing.In the scheme a slow molecular beam is produced from an effusive beam by surface velocity filtering.Then the velocity spread of the slow molecular beam is compressed by a buncher consisted of a series of electrodes.Following that the molecular beam with a narrow velocity spread is stored in a storage ring.Using ND₃ molecule as a tester,the feasibility of our scheme is analyzed theoretically and verified via numerical simulations that cover all the three manipulation processes.The results show that cold molecular samples can be prepared from a thermal gas reservoir and can be stored in the storage ring with more than 10 round trips.Our combined scheme facilitates the production and manipulation of polar molecules,offering new opportunities for basic researches and intriguing applications such as quantum information science and cold collisions.Next,a new scheme of a buncher which can improve the efficiency of bunching is proposed.Because the electrostatic buncher has a defect in some positions,which cause the transverse defocusing of the molecules,lots of molecules loss and the bunching efficiency is low.When combining the electric field with the magnetic field which can transversely focus the molecules,the loss of the molecules can be reduced and the bunching efficiency can be improved.Permanent magnet NdFe35 is used to produce the magnetostatic field,which has a magnetic trap of 0.5 Tesla.With the Monte Carlo simulation of OH radical,the bunching efficiency after 15 stages increases to 2.5 times in the combined electric and magnetic fields.