Effect of an aperture in atomic gravimetry

Abstract

There is a continuous interest in shrinking the dimensions of portable atomic gravimeters. This inevitably ends up truncating the Gaussian wings of the excitation laser beams whose effect has not been properly quantified yet. The diffraction pattern created from this aperture creates ripples in the wavefront in both the phase and the intensity. We calculate the shift in the measured value of an atomic gravimeter introduced by the phase variations in the wavefront. Fortunately, this shift has a Gaussian decay with the aperture size. For extended clouds, we observe a reduction of the effect thanks to an averaging over transverse positions with different values of the shift. Surprisingly, we found that the intensity variations also introduce an important correction to the photon recoil, which contributes at about the same level as the previous shift in the measurement of the gravitational acceleration. Our results should help decide how small an apparatus can be to guarantee a particular accuracy.