Reaching the nano-g with an absolute cold atoms gravimeter

This thesis present the latest work realized on the absolute colds atoms gravimeter of the LNE-SYRTE. To measure g, this device, called CAG, realize an atomic interferometer with Raman pulses on a free falling atomic cloud of Rubidium 87. The accuracy of the CAG’s measurements are limited by the Raman beam, its phase and intensity profile. During the thesis, the apparatus was moved to the Observatoire de Paris to be upgraded, in order to reduce these effects and extending the limits of the CAG further.

After the restart of the device, which able us to reach similar sensibilities than previously at 20×10⁻⁹·g Hz^−1/2, the studies related to the Raman beam have been continued. The manuscript details this work, which guides to study the stability of the intensity of each Raman beam, as well as the impact of inhomogeneity in the intensity profile. This inhomogeneity has been proven to cause a light shift distribution within the atomic cloud, resulting in a loss of contrast. This phenomenon also cause a bias on the measurement of g, of the order of 5×10⁻⁹·g, which is not eliminated by the measurement algorithm, and should be taken into account into the uncertainty budget. We also present the first results of the optimal control of the Raman transitions. This experimental method aims to improve the efficiency of the transitions and, consequently, the contrast of the interferometer.

atomic interferometry, gravimeter, inertial sensor, colds atoms

Full document (FR) : TEL-05035515