Studies of cold magnesium atoms in a magneto-optical trap – Niels Bohr Institute - University of Copenhagen

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Studies of cold magnesium atoms in a magneto-optical trap

PhD-defence: Nicola Malossi
Niels Bohr Institute

Jan W. Thomsen, Niels Bohr Institute

Isabelle Bouchoule, Campus Polytechnique, Paris
Guglielmo M. tino, Universita di Firenze

In this talk, after quickly and schematically introducing the main themes of the experimental investigation of cold neutral magnesium, the PhD work will be introduced and discussed. The three main experiments on the laser cooled and magnetically-optically trapped sample of neutral magnesium atoms, performed during the PhD work and arguments of the thesis itself, will be presented and the respective results shown and discussed. One of the main limitation of magnesium, towards the development of new frequency standard and in general for any precise measurement of the atomic parameters, is the relative high temperature achievable with standard laser cooling techniques. For these reason the first experiment, I will present, has been aimed to face such problem. A novel laser cooling technique, namely two-photon coherent laser cooling, has been developed and tested in our lab, consisting essentially in the laser cooling of a three-level driven atom in ladder configuration where the coherent coupling of the atomic states, typical of the driven three level system, can drastically modify the steady state populations of the atomic states and therefore modify both the laser cooling force and the diffusion property of the interaction, leading to a considerable change of the temperature of the sample. With the right choice of atomic parameters it is theoretically possible and experimentally proved to achieve temperatures lower than the ones due to the traditional laser cooling scheme (namely two-level Doppler cooling theory). A second experiment has been dedicated to the measurement of the lifetime of the triplet 3s3p3P1, using for the first time cold atoms. This kind of measurement is important both in the context of high precision measurements, where the triplet states and the intercombination optical lines (connecting 1S0- 3P transitions) are central, both theoretically, since the modeling of the two-electron atom have received in the past years great attention and many atomic parameters can be calculated with a high degree of precision. Since a discrepancy between theory and experiment is still evident, our experiment aims to shine new light on the matter by using a technique which was novel for the specific measurement, leading thus to a new error systematic compared to the previous experimental protocols.

Lastly by exploiting another important feature of the even magnesium isotopes, being a very good approximation of a two-level atom, if the non-degenerate ground state and the first exited are only considered, a number of experiments have been performed to test the Doppler laser cooling theory for two level atoms with the "release and recapture".