| Summary: | 碩士 === 國立成功大學 === 光電科學與工程研究所 === 92 === We constructed a Double Magneto-Optical Trap (MOT) System in order to trap and cool down Cs atoms. The vacuum part of the system is composed of two independently running vacuum system connected with a low conductance tubing. The part near Cs atom source will be at lower vacuum and the other part at high vacuum, which is called differential pumping.
Double MOT System is preferred because at lower vacuum side MOT could collect Cs atoms much faster and could be homogeneously pushed into higher vacuum area, where MOT could have longer lifetime for further cooling and experiments. Lower background gas pressure can save more time for evaporative cooling, further compression to arrive lower temperature and higher phase density. By now our system have 2x10-8 Torr at lower vacuum side and 5x10-10Torr at higher vacuum side.
Magnetic field is constructed by 2 coils, each in 120 turns 1/8” copper tubing and after cooling water running through it could bear 40A at the temperature of 43℃.These coils are spatially oriented in Anti-Helmholtz scheme and generate 2.15 Gauss/cm-A at trap center.
We use one TEC100 (Sacher Lasertechnik) for main MOT beam and the other for repumper beam. TEC100 uses grating feedback to reduce the laser bandwidth to 2MHZ, which is suitable for hyperfine structure. MOT beam is divided into six beams and conducted to cross as three pairs of counter propagating beams at MOT center. Repumper beam is directly conducted to run across MOT center in order to pump off-resonant atoms back to cooling cycles. These two laser uses Doppler-Free Saturation Absorption Spectroscopy (DFSAS) for frequency lock.
After accomplishment of this system, we could do optical lattice, dipole trap, BEC, hyper fine structure, atom/molecules collisions at ultracold temperature and basic Quantum Information Science (QIS) experiments.
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