Preparation of an optically-trapped degenerate Fermi gas of 6Li: Finding the route to degeneracy

This thesis describes the first all-optical production of a degenerate Fermi gas of atoms. In the experiment, a Magneto-Optical-Trap (MOT ) containing ≃ 1−3 × 108 atoms of 6Li at a temperature of 150 μK is used to load an optical trap formed by the focus of a 65 W CO₂ laser beam. The optical potential has a depth of 700 μK and trap oscillation frequencies of 6.6 kHz in the radial direction and 275 Hz in the axial. Approximately 3 × 10 6 atoms are transferred to the optical trap and the MOT is extinguished. A uniform magnetic field of 100 G is applied to the atoms, tuning the s-wave scattering length to ≃ −100 a₀. This initiates free evaporative cooling in the sample. After 6s, evaporation has stagnated and 1.3 × 106 atoms remain at a temperature of 50 μK. The intensity of the CO₂ laser is then lowered to drive forced evaporative cooling. After 60s of forced evaporative cooling, 1 × 105 atoms remain at a temperature ≤ 4 μK. For this number of atoms, the Fermi temperature, T_F = 8 μK. With T/T_F ≤ 0.5, the sample is clearly degenerate.; In addition to the experimental work, this thesis presents three theoretical results of note: (1) The development of a Monte-Carlo model for simulating a classical or near-classical gas in a Gaussian well. This model extends previous techniques for harmonic wells to a case which approximates the potential well of an optical trap. The application of the model to temperature measurement, trap frequency measurement, and cloud size in an anharmonic potential is presented. (2) The development of a Fokker-Planck approach to studying the evolution dynamics of trap populations in response to fluctuations in the trapping potential. The heating that results from such fluctuations was a primary factor in early failures of optical traps. Understanding these heating processes allowed our group to construct the first optical trap capable of storing atoms for more than a few seconds. (3) The development of an analytical treatment which relates the signal-to-noise ratio of atomic imaging techniques to the physical characteristics of the imaging equipment and the specific imaging technique. This treatment was used to design the imaging system used in the aforementioned experiments.