Characterization of systematic errors due to intensity inhomogeneities of Raman beams in a cold-atoms absolute gravimeter

Correlations between the internal and external degrees of freedom of neutral atoms enable state-of-the-art accuracy and sensitivity in inertial sensors. This thesis presents the latest developments in the absolute cold-atom gravimeter (CAG) of the LTE, based on momentumstate interferometry using Raman transitions in a freely falling atomic cloud of ⁸⁷Rb.

We identify intensity inhomogeneities as a primary source of contrast loss in the CAG and highlight the role of non-resonant interactions resulting from the counterpropagating geometry of the Raman beams. Following optimization of the optical setup, the interferometer contrast improved by nearly 10 %, with local intensity-related features successfully eliminated. Additionally, we identified bias phases arising from intensity variations, predominantly during the mirror pulse. We introduce a dynamical method for evaluating these phase shifts, which generalizes the traditional adiabatic approximation. This method enables us to distinguish between phase shifts caused by two-photon processes and those of other origins. Crucially, it links the population of stray momentum states to the accumulation of nonlinear phase shifts at the interferometers output ports.

We report a systematic bias in the measurement of g at the level of 5×10⁻⁹ g, attributed to intensity inhomogeneities, and a sensitivity of 20×10⁻⁹ g Hz^−1/2.

atomic interferometry, gravimeter, inertial sensor, adiabatic approximation.

Full document (EN) : TEL-05450855