Phoonthong, P.; (2012) State-insensitive traps for caesium atoms. Doctoral thesis , UCL (University College London).

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Abstract

State-insensitive traps are an important tool for precision spectroscopy. In these traps both the ground and excited state of the relevant atomic transition are shifted by the same amount. To obtain state-insensitive trapping, a specific trapping wavelength - called the "magic wavelength" - must be used. This thesis describes state-insensitive trapping of caesium atoms, as realised by using a trapping laser beam at the magic wavelength of 935.6 nm. Two different experimental setups were realised and characterised. The first set of experiments provided the characterisation of a singlewell state-insensitive trap, produced by using the laser beam from a Tisapphire laser. The trap lifetime was determined as a function of the trap depth, with the largest lifetime of 203 ms measured for a trap depth of 2.4 mK. Further improvement in the trap lifetime was obtained by applying a depumper laser beam, which prepared the atoms in the lower ground state. This suppresses hyperfine changing collisions, and the lifetime was increased to 3.6 s as a result. Ultimately, the lifetime was limited by the pointing instability of the dipole trap beam and the background gas collisions. A second experimental setup was then realised, to reduce the background gas collisions, which is the limitation of lifetime in the first setup. Furthermore, the imaging system was upgraded to reduce the background noise, and a MOPA system was used to produce the state-insensitive trap. In a second set of experiments, a single-well trap and a 1D optical lattice were compared to evaluate the suppression of two-body collisions in the 1D lattice case.

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