Single-impulse magnetic focusing of launched cold atoms

Abstract

This thesis concerns the use of pulsed magnetic lenses with cold atoms. Specifically, an experiment was designed and built to focus a launched cloud of cold rubidium atoms. An atomic fountain was realised, based on launching a compact cold cloud of atoms using the technique of moving molasses. Analytical and numerical simulations were conducted to formulate the optimum strategies for focusing. Focusing aberrations are investigated and characterised, and techniques for minimising their deleterious effects are presented. A Baseball Lens was constructed to enable the experimental 3-dimensional focusing of launched cold atoms with a single magnetic impulse. Typically 7x1๙ 85Rb atoms were loaded into a magneto-optical trap (MOT), before undergoing an optical molasses stage. Subsequently a moving molasses phase was realised to launch the atoms vertically at a speed of approximately 2 m տ՜՛ to bring them to an apex 20.5 cm above the MOT in a remote vacuum chamber. During their flight the atoms were pumped into the weak-field-seeking 5(^2)S(_2)[ғ = 3,m = з) state. The centre of the Baseball Lens was located 16.5^ cm above the MOT. Fluorescence images were taken at the apex of flight to characterise the width of the focussed cloud. Results were obtained for four different configurations of the Baseball Lens, which varied the relationship between the axial and radial angular frequencies of the lens. Compact focussed clouds were seen for all four configurations with a minimum observed volume of 60 士 3 mm(^3)which is a factor of 17 smaller than the unfocussed cloud. 3-dimensional magnetic focusing of cold atoms with a single magnetic impulse has been observed for the first time.