Sensitivity improvement of atomic fountain gravimeter using a hollow laser beam

Abstract

An atom gravimeter is an apparatus with very high precision and sensitivity for measuring gravity based on the interference of atomic wave packets. This instrument has applications in fundamental physics research, geophysics research, and exploration and monitoring. Our atom gravimeter is configured using a 50 cm atomic fountain. We employ 87Rb atoms as the test mass within an atom Mach-Zehnder interferometer, utilizing stimulated Raman transition techniques to manipulate the interferometer path. This study has two main objectives: the design and setup of an atom gravimeter based on an atomic fountain configuration, and the investigation of sensitivity improvements using a hollow laser beam in the Mach-Zehnder interferometer. For the first objective, we designed the gravimeter to include a 2D+ magneto-optical trap (2D+ MOT) and a 3D magneto-optical trap (3D MOT) to prepare a cold 87Rb atoms cloud, an atom interferometer section, and a detection system based on fluorescent imaging. For the second objective, we calculated the sensitivity improvement of the atom gravimeter. Assuming the 3D MOT produces 109 87Rb atoms at a temperature of 20 µK, we determined the hollow beam geometry to be a 2 cm tube diameter with a 2 mm tube thickness. Our calculations show that only about 25% of the atoms can be detected by the non-hollow beam gravimeter, resulting in a sensitivity of 2.528×10-5g per measurement. In contrast, the hollow beam confines all the measuring atoms within the imaging region, increasing the sensitivity to 6.4×10-6g per measurement, thus improving the sensitivity by 74.61%. However, we did not calculate the scattering rate of the atoms within the hollow beam region, which will need to be addressed in future work.