AbstractsPhysics

This thesis presents work performed to obtain an optical mask for conducting matter-wave interferometry experiments with ultra-cold rubidium-85 atoms. The optical mask is essentially an absorptive diffraction grating made of light, and it can imprint a periodic density pattern on a cloud of atoms with a period of half the wavelength of the light used. The mask has an analogous effect to quickly passing a diffraction grating through the cloud, removing atoms located at the nodes of the grating (though the optical mask depumps atoms to a different hyperfine ground state rather than actually removes them). The mask should be useful in performing precision measurements of physical constants such as the fine-structure constant α, and acceleration due to gravity g. The thesis briefly expounds major historical developments in atom interferometry and laser cooling. Prerequisites for an optical mask include a functioning magneto-optical trap, and the ability to perform polarisation-gradient cooling on trapped atoms. The theory of these two techniques is reviewed and the principle of the the optical mask is explained. The experimental apparatus that was constructed to realise the optical mask is described, and technical developments made along the way are presented. Finally, aspects of the experiment relevant to the optical mask are characterised. The experiment can reliably produce samples of cold atoms at temperatures of around 10 µK, and can use the cold atoms as an optical frequency reference accurate to ~ 1 MHz. Clear evidence that the cloud of atoms is being density-modulated by the optical mask is presented. Improvements required to make the experiment into a fully-functioning interferometer are also discussed.