Laser Cooling And Trapping Of Fermionic ~6Li Atoms

To understand quantum many-body interaction in the ultra-cold gases is very important in the field of atomic, molecular and optical physics. Collisional interaction between atoms can be tuned by the so-called Feshbach resonance with an external magnetic field or laser field. The sign and magnitude of an s-wave scattering length that characterizing the interaction strength can be accurately changed, therefore one can study the molecular BEC, BCS superfluid of atom pairs and BEC-BCS crossover in such ultra-cold Fermi gases. In addition, by controlling the optical trapping potential, the low dimensional strongly interacting matter can be realized, which shows the rich phase diagrams, such as phase splitting, the crystal phase, pairing mechanism, the trimer of long lifetime, and even polar ultra-cold molecules with long-range dipole-dipole interaction. In the above experimental study,6Li plays an important role. It is one of the two stable Fermi atoms in the alkali metal elements. Although 6Li is the lightest alkali atom which can be laser cooled, it has the strongly atoms interaction. It has a large background scattering length (-2200 ao, ao is the Bohr radius) in the absence of an external magnetic field. More importantly, there are two Feshbach resonances in the external magnetic field:a resonance with the width of 300 Gauss and the other resonance with the width of 0.2 Gauss. These features make 6Li as an ideal candidate to understand and study many-body physics.The starting point of studying Fermi degeneracy and strong interaction is to implement the magneto-optical cooling and trapping of atoms. The main work of this thesis is to build an experimental system for the cooling and trapping of the fermionic 6Li atoms. We realize the magneto-optical trap (MOT) of Fermi atoms by the laser cooling. We get the cold atomic samples of high density and study the loading dynamics of cold atoms. The 6Li MOT is an important step toward the quantum degeneracy, the MOT of high-density, fast loading, low temperature, high repetition and excellent quality set a playground for the dipole trap, evaporative cooling and many-body strong interaction.The main results of this thesis are as follows:1, Designed and realized the ultrahigh vacuum system for the laser cooling. Using the mechanical molecular pump, sputter ion pump, titanium sublimation pump and vacuum ionization gauge, the two-stage vacuum chamber is built. The vacuum of first chamber is 4×10-11 Torr and the vacuum of second chamber is 3×10-11 Torr.2, Designed Zeeman slower of 6Li atom realized one-dimensional cooling. The optimized Zeeman slower can slow the atom oven from 1100m/s to 50 m/s axially, and to 4 m/s radially.3, Built a laser system for the MOT and realized Fermi 6Li cold atoms. In the experiment, we use a single laser to achieve the cooling lights and repump lights for the cooling and trapping of 6Li atoms.108 atoms can be loaded from Zeeman slower in 10 s. The lifetime of the atom in the MOT is about 100 s.4, Study the loading dynamics of cold atoms in a MOT. We measure the loading rate, one-body collisional loss, the atoms number as the functions of the oven temperature, the cooling power, the gradient of magnetic field, respectively. The calculations based on the gas kinetics and scattering collisional theory agrees very well with the measured data.