Techniques in laser cooling and trapping of atomic ytterbium.

摘要

This dissertation reports an experimental and theoretical study of laser cooling and trapping of atomic Ytterbium (Yb). Studies focus on the radiative transfer of momentum from Yb atoms to the surrounding light field using the strong (6s2)1S₀–(6s6p) 1P₁ transition at 398.9 nm and the weak intercombination (6s2)1S₀–(6s6p)3P ₁ transition at 555.8 nm. An overview of theoretical principles underlying the techniques of laser cooling and trapping is provided, with deviations from the two-level model due to atomic or experimental system details being noted. Properties of the internal level structure of Yb relevant to radiative coupling between the ground and excited states under trap conditions are presented. Experimental apparatus required to perform these studies are described in detail, including laser systems to produce light at 398.9 nm and 555.8 nm for cooling and probing, an atomic beam Zeeman slower and magneto-optical trap (MOT) for the 1S₀–1P ₁ transition, and a MOT for the 1S₀– 3P₁ transition.; We demonstrate the one dimensional cooling effects of resonant 398.9 nm light on counter-propagating atomic Yb using the techniques of Doppler cooling and Doppler compensated slowing. Expanding these techniques to three dimensions, a 1S₀–1P₁ Yb MOT has been formed that exhibits a power-dependent lifetime resulting from branching via cascade radiative decay to the long-lived (6s6p) 3P_2,0 metastable excited-states. Measurements of trap lifetime for various trapping beam powers and ambient background pressures allows a determination of the effective 1P₁– 3P_2,0 decay rate and the Yb collisional cross-section, respectively. Utilizing the presence of a spectrally narrow 1S ₀–3P₁ transition, new fluorescence techniques for in situ probing of trap characteristics are introduced.; Studies of a weak 1S₀–3P ₁ Yb MOT are carried out to investigate narrow line trap environments and realize improvements over the 1S₀– 1P₁ MOT. An experimental apparatus has been constructed and investigated theoretically by Monte Carlo modeling of the absorption/emission process. Simulations show temperatures within a factor of 2 of the Doppler limit and approaching the maximum capture velocity can be realized simultaneously for suitable trap parameters. The use of frequency modulated light fields to improve performance in the trap environment is investigated.