Generation And Research Of The Continuous-wave, Cold Polar Molecular Beams

In recent years,cold molecules with rich internal level structure,as the basic unit in physics and chemistry,have open up new opportunities for molecular precision spectroscopy and measurements of some constants of physics and chemistry,studies of cold collisions and cold chemistry,quantum information processing and so on.The study of generation and application of cold molecules has attracted more and more scientists.In this thesis,the principle,experiments and recent progress on cooling, trapping and manipulating molecules have been first briefly introduced and reviewed. Secondly,the generation of cold continuous CH₃CN molecular beam at room temperature using quadrupole electrostatic bended guiding is theoretically and experimentally studied.Afterwards,a new scheme of controllable surface trapping for cold atoms or cold paramagnetic molecules using 2D array of current-carrying wires is proposed.Finally,our research work is summarized and the future investigation is briefly looked ahead.We theoretically study the bended guiding(also named the low pass energy filter) for continuous CH₃CN molecular beam using quadrupole electrostatic field.We calculate the distribution of electric field,the Stark shift of rotational energy level and their populations of CH₃CN,a kind of typical symmetric-top molecule.We study the dynamic process of molecules in the guiding with Monte-Carlo simulation.When the voltage of electro-rods is 3 KV,we obtained the velocity distributions of guided molecular beams,and the longitudinal and transverse temperatures are T_Z=2.2K,T_ρ= 420mK,and the guiding efficiency is1.96×10^-5.We conclude that the relationship between the temperature of molecular beams and the guiding voltage is linear,and the dependence of the guiding efficiency on the voltages is quadratic.Furthermore,we simulate the guiding process of cryogenic molecular beam(5K)using different voltages for the two bends.When the guiding voltages on the first and the second bent electrodes are 1KV and 0.5KV,respectively,the temperatures of the guided molecular beam are T_Z=301mK,T_ρ=28.6mK,and the guiding efficiency is9.0×10^-4.Our results show that using cryogenic molecular beam source,contrast to source with room temperature,we can not only obtain cold molecules with lower temperature,but also with higher flux.We experimentally study the bent quadrupole electrostatic guiding of CH₃CN molecular beam at room temperature.The beam source system,vacuum system,sets of electrodes and ceramics,high voltage pulse time-sequence control system,time of flight(TOF)measurement system are introduced.We obtain a cw cold molecular beams whose velocity distributions and temperatures are coincident with theoretical simulations.When the guiding voltage is 1KV,and the pressure of source is 50Pa,we generate a cw cold CH₃CN molecular beam with a temperatures of T_Z =520mK and T_ρ=42.3mK.We also measure the velocity distributions,temperatures and guiding efficiencies for different guiding voltage and source pressure.We find that the temperature decrease linearly with reducing voltage,and the relationship between guiding efficiency and voltage is quadratic.Moreover,we study the divergent angle of the output molecular beam.With the increasing of voltage,the angle first decrease exponentially,and then tend to be a definitive value.We study the focusing effects of hexapole electrodes,and calculate the inhomogeneous electric field formed by hexapole electrodes and the dipole forces suffered on the molecules.Using the former results of our theoretical and experimental study,we simulate the trace of molecular beam in the hexapole electrostatic field.Our results of simulation are in good agreement with the theoretical calculated ones.We propose a novel schemes to form surface MOLs and MLs by using arrays of square current-carry wires combined with bias magnetic fields.Two arrays of magneto-optical traps(MOT)or Ioffe magnetic traps can be formed symmetrically above and below the wire array fabricated on the substrate.We calculate the spatial distributions of magnetic fields and their gradients and curvatures from each well.We find that our double-layer traps can be changed as a single-layer one by adjusting the current in the wire or changing the additional bias field in the vertical direction. Furthermore,the MOTs can be continuously changed to Ioffe traps by adjusting the horizontal bias field.Finally,we simulate the loading process of a cloud of atoms from magneto-optical surface traps to Ioffe surface traps.In the process of evolution, the density and the temperature of cold atoms will be increased.Our study show that the scheme can be used to form cold atom lattice and cold molecule lattice on a chip, and used to perform quantum computing and its information processor.