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Review of Scientific Instruments

De-coupling the Coriolis effect from Raman beams alignment in a fountain atom gravimeter

Qin Luo, Hang Zhou, Li Li, LeLe CHEN, Xiaochun Duan, Zhong-Kun Hu, Min-Kang Zhou

Published Feb 1, 2026• 0 citations
Publisher

Abstract

The alignment of Raman beams is important for high-precision atom interferometry gravimeters, and tilt modulation experiments are usually carried out to calibrate the direction of Raman beams. However, the Coriolis effect could be changed during the tilt modulation experiment, thus introducing a deviation in the alignment of Raman beams. In this work, a method of rotating the sensor head by 90° to eliminate the impact of the Coriolis effect on Raman beams' alignment in a fountain atom gravimeter was proposed and demonstrated experimentally. Using this method, the alignment uncertainty of the Raman beams in the atom gravimeter was reduced to 11 μrad, which contributed an uncertainty of less than 0.1 μGal (1 μGal = 1 × 10-8 m/s2) to the gravity measurement. Further simulations explained the experimental results and pointed out a way to reduce the Coriolis effect in atom gravimeters.

DOI
10.1063/5.0308195

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The alignment of Raman beams is important for high-precision atom interferometry gravimeters, and tilt modulation experiments are usually carried out to calibrate the direction of Raman beams. However, the Coriolis effect could be changed during the tilt modulation experiment, thus introducing a deviation in the alignment of Raman beams. In this work, a method of rotating the sensor head by 90° to eliminate the impact of the Coriolis effect on Raman beams' alignment in a fountain atom gravimeter was proposed and demonstrated experimentally. Using this method, the alignment uncertainty of the Raman beams in the atom gravimeter was reduced to 11 μrad, which contributed an uncertainty of less than 0.1 μGal (1 μGal = 1 × 10-8 m/s2) to the gravity measurement. Further simulations explained the experimental results and pointed out a way to reduce the Coriolis effect in atom gravimeters.
The Coriolis effect can introduce significant systematic errors in atom interferometers. This study examines the coupling effect between the Coriolis effect and the Raman beams–orientation in a fountain atomic gravimeter. Theoretical analysis indicates that the Coriolis effect is correlated with the orientation of the Raman beams, and tilt modulation experiments were conducted to substantiate this correlation. Furthermore, by aligning the orientations of the atomic fountain, the vacuum chamber, and the Raman mirror, we achieved simultaneous suppression of both the Coriolis effect and the tilt effect to sub- μ Gal levels in a high-precision atomic gravimeter. This work offers guidance on assessing systematic errors in high-precision atomic gravimeters.
The sensitive axis of an atom gravimeter is defined by the direction of the Raman lasers. Any tilt of the Raman lasers with respect to the vertical direction introduces systematic errors in gravity measurements. In this work, we report a determination of the tilt of Raman lasers, where the fringe of the atom interferometer is scanned by varying the tilt, rather than the phase, of the Raman lasers. Unlike the periodic cosine fringes typically used in atom interferometers, the fringe obtained by changing the tilt, referred to as the tilt-scanned fringe, is aperiodic in tilt and exhibits a shift due to the presence of a nonzero tilt. The tilt-scanned fringe is highly sensitive to the tilt-caused shift, enabling convenient and precise determination of the Raman laser tilt in atom gravimeters. We demonstrate that one tilt-scanned fringe, corresponding to a tilt measurement sampling time of 13 s, can determine the tilt with a typical precision of about $30\phantom{\rule{0.28em}{0ex}}\textmu{}\mathrm{rad}$ in our developed atom gravimeter. The short-term sensitivity and measurement accuracy of the tilt-scanned fringe method were evaluated, demonstrating performance comparable to conventional tilt determination techniques. We expect this method to offer a convenient solution for Raman laser alignment in atom gravimeters and enhance the efficiency of absolute gravity surveys.
The mechanism of light-shift-related uncertainty in an atom-interferometry gravimeter is investigated systematically, which arises from the inhomogeneous intensity of Raman beams and the Gaussian distribution of an atomic cloud. Experiments using atom interferometry are performed to verify this systematic error by directly modulating the integration time TTT and the intensity ratio of Raman laser beams. Using our method, the uncertainty of gravity measurements contributed by the single-photon light shift in an atom gravimeter can be corrected to a $\mathrm{sub}\ensuremath{-}\ensuremath{\mu}\mathrm{Gal}\phantom{\rule{0.28em}{0ex}}(1\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{Gal}=1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}\phantom{\rule{0.28em}{0ex}}\mathrm{m}/{\mathrm{s}}^{2})$ level.
The cold atom absolute gravimeters are intrinsically sensitive to its orientation due to the Coriolis effect, which should be understood clearly and compensated for field applications. The sensitivity on the orientation for a free-fall atom gravimeter is investigated in this paper. The apparatus is simplified and improved a lot such that fast adjustment and measurement could be carried out within 20 minutes. From the experimental results, it is found that the orientation angle has a dominant influence on the absolute gravity measurement, especially when the horizontal velocity of atoms is non-negligible. Besides, the magnitude and direction of average horizontal velocity of the detected atoms are obtained in this experiment. In particular, the direction of East-West has been measured by the atom gravimeter itself, such that gravity bias arising from Coriolis effect is estimated precisely.
The technology of electro-optic modulation is one of the several methods of generating the Raman beams. The experimental system based on this method is simple and much easier to implement, and the environmental adaptability is strong as well. However, this kind of modulation technology will produce additional laser lines, which may affect the measurement accuracy of cold atom gravimeter. Based on a homemade transportable cold atom gravimeter, the influence of Raman sideband effect on the accuracy of cold atom gravimeter is investigated in this paper. We analyze in detail the relationship between Raman sideband effect and some experimental parameters, such as the height of Raman retro-reflection mirror, the time of free fall of the atoms, the detuning of Raman laser, etc. It is found that those parameters have a dominant influence on the measured gravity resulting from Raman sideband effect. Besides, it is also found that the gravity measurements will be sensitive again to some experimental parameters in the case of Raman sideband effect while these parameters are usually insensitive in case of laser system without sideband effect. Finally, we investigate the relationship between Raman sideband effect and Raman detuning, and presente a method of evaluating the gravity induced by Raman sideband effect. The experimental results in this paper can provide a reference for reducing the influence of Raman sideband effect on the accuracy evaluation of cold atomic gravimeter.
Cold atom free-fall interferometers now realize state-of-the-art precision inertial sensors, opening perspectives towards embedded devices for applications and fundamental physics tests on earth and in space. The acceleration of gravity can be measured in a stimulated Raman transition interferometer where the acceleration under gravity of a cloud of freely falling atoms is sensed by three Raman pulses allowing to split, reflect and interfere atomic wave packets [1]. The gravimeter developped at SYRTE allows to measure the acceleration of gravity at state-of-the-art performances compared to the best classical absolute gravimeters, with a sensitivity of 2×10−8g over 1s and an exactitude of 5×10−9 g [2]. This exactitude is currently limited by wavefront aberrations of the lasers, sampled by residual transverse trajectories of the molasse-cooled cloud over the free fall. Unbalanced transverse trajectories will also bias the measurement due to Coriolis effect [3]. We will investigate the use of a colder atom source to reduce these systematic effects, by implementing Bose-Einstein condensation of the initial cloud, allowing both better position control and better focusing of our source.