The Experiments For Laser Cooling,Trapping And Coherent Manipulations Of Lithium Atoms

As the smallest atomic number of alkali metal elements, lithium has the characteristics of small mass and big recoil velocity. Its large photon-recoil energy is a favorable factor for large area atom interferometers which can be used for precision frequency measurements of recoil energy and the fine structure constant. In addition, selecting lithium atoms for weak equivalence principle (WEP) test also has broad prospects. However, due to the special energy level structure of lithium atoms, traditional sub-Doppler cooling is hard to work on lithium atoms, this also affects the development of lithium cold atom interferometer. In this thesis, with the goal of developing lithium cold atom interferometer, I have done works on the atom cooling, trapping, sub-Doppler cooling, Raman transition and Rabi oscillations of 7Li. The main innovative research works and results are listed as follows:(1) To obtain the source of atoms, the Zeeman slower is realized in our experiment and the speed of lithium is slowed down successfully from 700 m/s to 70 m/s. After combining with magneto optical trap (MOT), I have got MOT signal of lithium. And then I detect the number (1.2×109) and temperature of atoms, by using the compressed MOT (C-MOT) the atomic temperature is further reduced to 220±30 μK.(2) Two new sub-Doppler cooling methods, the Sisyphus cooling and Gray molasses cooling. By using the Sisyphus cooling method, the lithium atoms are cooled below the Doppler limit for one dimensional cooling. Using Gray molasses cooling scheme, the one dimensional Gray molasses of lithium is captured.(3) Preliminary exploration of lithium cold atom interferometer is performent using the two-photon detuning of 1.6 GHz. We have realized the Raman transition and got the Raman resonant peak. The center of the resonance peak in 803.518 MHz and the half high width is 16.6 kHz. After scanning the pulse time of Raman beams, I achieved the Rabi oscillation curve, which is used for the choice of the time of π pulse.(4) On the need for the experiment, we designed a beam expander which can export laser beams with different polarizations, that plays an important role in our experiments.(5) In order to meet the need of frequency stabilization of Raman beam, the modulation transfer spectrum (MTS) of lithium is studied in detail, and the Raman beam is locked successfully by the MTS.