Tilt adjustment for a portable absolute atomic gravimeter

For an atomic gravimeter,the measured value of the Earth’s gravity acceleration g is the projection of the local gravity on the direction of Raman laser beams.To accurately measure the g,the Raman laser beams should be parallel to the g direction.We analyze the tilt effect of the Raman beams on g measurement and present a general method for the tilt adjustment.The systematic error caused by the tilt angle is evaluated as 0(+0,0.8)µGal(1µGal=10 nm/s^2)and the drift is also compensated in real time.Our method is especially suitable for the portable atomic gravimeter which focuses on the mobility and field applications.

Portable atomic gravimeter operating in noisy urban environments

The gravimeter based on atom interferometry has potential wide applications on building gravity networks and geophysics as well as gravity assisted navigation. Here, we demonstrate experimentally a portable atomic gravimeter operating in the noisy urban environment. Despite the influence of noisy external vibrations, our portable atomic gravimeter reaches a sensitivity as good as 65 μGal/√Hz and a resolution of 1.1 μGal after 4000 s integration, being comparable to state-of-the-art atomic gravimeters. Our achievement paves the way for bringing the portable atomic gravimeter to field applications.

Michelson laser interferometer-based vibration noise contribution measurement method for cold atom interferometry gravimeter

The measurement performance of the atom interferometry absolute gravimeter is strongly affected by the ground vibration noise.We propose a vibration noise evaluation scheme using a Michelson laser interferometer constructed by the intrinsic Raman laser of the atomic gravimeter.Theoretical analysis shows that the vibration phase measurement accuracy is better than 4 mrad,which corresponds to about 10-^10 g accuracy for a single shot gravity measurement.Compared with the commercial seismometer or accelerometer,this method is a simple,low cost,direct,and fully synchronized measurement of the vibration phase which should benefit the development of the atomic gravimeter.On the other side,limited by equivalence principle,the result of the laser interferometer is not absolute but relative vibration measurement.Triangular cap method could be used to evaluation the noise contribution of vibration,which is a different method from others and should benefit the development of the atomic gravimeter.

Calibration of the superconducting gravimeter based on a cold atom absolute gravimeter at NIM

The scale factor of a superconducting gravimeter(SG) is usually calibrated by using simultaneous and co-located gravity measurements with the FG5-type absolute gravimeter(AG). In this paper, another new kind of absolute gravimetercold atom gravimeter(CAG) is first reported to calibrate the SG. Five-day side-by-side gravity measurements have been carried out by using our CAG(NIM-AGRb-1) to calibrate the SG(iGrav-012) located at Changping Campus of the National Institute of Metrology(NIM) of China. A weighted least-squares method is applied to determine the scale factor and the result is given as(-928.01 ± 0.73) nm·s^(-2)·V^(-1) with a precision of 0.79‰. We have demonstrated that a calibration precision of 1‰ level can be achieved after 3 days of parallel observations at spring tide. The obtained calibration results are then compared with the previous calibration by FG5 X-249, which shows that the calibration precision obtained by using NIM-AGRb-1 was slightly higher than FG5 X-249 with the same time interval. The factors affecting the calibration precision are analyzed in the calibrations by means of different AGs. Finally, several calibration experiments for SG iGrav-012 are discussed. The final scale factor is estimated as(-927.58 ± 0.36) nm·s^(-2)·V^(-1) with an accuracy of 0.39‰. Our main results demonstrate that the CAGs can be used for high-precision calibrations of SGs.

Investigation of the thermal adaptability for a mobile cold atom gravimeter

The cold atom gravimeter offers the prospect of a new generation of inertial sensors for field applications. We ac- complish a mobile atom gravimeter. With the compact and stable system, a sensitivity of 1.4× 10-7 g.Hz-1/2 is achieved. Moreover, a continuous gravity monitoring of 80 h is carried out. However, the harsh outdoor environment is a big challenge for the atom gravimeter when it is for field applications. In this paper, we present the preliminary investigation of the thermal adaptability for our mobile cold atom gravimeter. Here, we focus on the influence of the air temperature on the performance of the atom gravimeter. The responses to different factors （such as laser power, fiber coupling efficiency, etc.） are evaluated when there is a great temperature shift of 10 ℃. The result is that the performances of all the factors deteriorate to different extent, nevertheless, they can easily recover as the temperature comes back. Finally, we conclude that the variation of air temperature induces the increase of noise and the system error of the atom gravimeter as well, while the process is reversible with the recovery of the temperature.

Effect of Raman-pulse duration related to the magnetic field gradient in high-precision atom gravimeters

The effect of the Raman-pulse duration related to the magnetic field gradient, as a systematic error, is playing an important role on evaluating the performance of high-precision atomic gravimeters. We study this effect with a simplified theoretical model of the time-propagation operator. According to the typical parameters, we find that this effect should be taken into account when the gravimeter reaches an accuracy of 10^-10g, and the larger the pulse duration is, the more obvious the systematic effect will be. Finally, we make a simple discussion on the possibility of testing this effect.