Maher - McWilliams, C; (2013) Creation, trapping and manipulation of a cold argon gas. Doctoral thesis (PhD), UCL (University College London).

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Abstract

This thesis describes the construction and characterisation of a unique cold argon atom source for sympathetic cooling of molecules. Argon atoms were laser cooled from their lowest lying metastable state using the 4s[3/2]2 → 4p[5/2]3 transition at 811.5 nm. A magneto-optical trap (MOT) was used to cool the metastable argon (Ar*) atoms to 73.2 ± 0.4 μK and trap them at a density of 3.93 × 10^9 cm-3. Cooling was facilitated using an external-cavity diode laser which was frequency-stabilised to the cooling transition using a magnetic dichroism technique. This was the first application of this technique to a plasma operated at our pressures where the applied magnetic field affected the gas behaviour. The Ar* atoms in the MOT were used to demonstrate chirped optical Stark acceleration for the first time. Atoms were accelerated up to velocities of 191 ± 1 ms-1 while maintaining narrow energy spreads in the accelerated ensemble (30-100 mK). The acceleration occurred over tens of nanoseconds and on micrometre length scales. Control over the number of particles accelerated was achieved by tailoring the depth of the optical lattice potential. Monte Carlo numerical simulations of acceleration were used to fit experimental results and study the dynamics of particles over the acceleration duration. Trapping of Ar* atoms in a quasi-electrostatic trap (QUEST) has also been demonstrated. The QUEST was formed at the focus of a 100 W laser beam with a wavelength of 10.6 μm. A trap lifetime of 18.3 ± 0.3 ms was measured.

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