Improving the Fringe Contrast in an Atomic Gravimeter by Optimizing the Raman Laser Intensity

As the expansion of the atomic cloud's diameter relative to the Gaussian Raman beam in an atom interferometer, the interaction between them would be reduced. Such an effect can decrease the effective Rabi frequency and lower the state transfer efficiency of the Raman laser, which finally reduces the fringe contrast and the sensitivity of the atom interferometer. In this work, we demonstrate experimentally that the fringe contrast can be improved by optimizing the laser intensities of three Raman pulses, and find that the criterion for the optimized Raman laser intensities should be the Raman pulse efficiency rather than the Rabi frequency. In the case of an atomic gravimeter, our method obtains an obvious enhancement of the fringe contrast when T > 60 ms and the maximum contrast enhancement is similar to 5.1% (from 25.3% to 26.6%) at T = 120 ms. These results could be beneficial for atom-interferometer-based inertial sensors, including but not limited to the atomic gravimeter, gravity gradiometer and gyroscope.