Accurate trajectory alignment in cold-atom interferometers with separated laser beams

Abstract

Cold-atom interferometers commonly face systematic effects originating from the coupling between the trajectory of the atomic wave packet and the wave front of the laser beams driving the interferometer. Detrimental for the accuracy and the stability of such inertial sensors, these systematics are particularly enhanced in architectures based on spatially separated laser beams. Here we analyze the effect of a coupling between the relative alignment of two separated laser beams and the trajectory of the atomic wave packet in a four-light-pulse cold-atom gyroscope operated in fountain configuration. We present a method to align the two laser beams at the 0.2 µrad level and to determine the optimal mean velocity of the atomic wave packet with an accuracy of 0.2 mm · s −1 . Such fine tuning constrains the associated gyroscope bias to a level of 1 × 10 −10 rad · s −1 . In addition, we reveal this coupling using the point-source interferometry technique by analyzing single-shot time-of-flight fluorescence traces, which allows us to measure large angular misalignments between the interrogation beams. The alignment method which we present here can be employed in other sensor configurations and is particularly relevant to emerging gravitational wave detector concepts based on cold-atom interferometry.

High-accuracy inertial measurements with cold-atom sensors

“…If the bias associated with the imperfect atomic trajectories is con- trolled at a sufficient level (Ref. 135 ), then stability levels in the range of 10 −12 rad.s −1 can be anticipated.…”

Self-alignment of a large-area dual-atom-interferometer gyroscope using parameter-decoupled phase-seeking calibrations

“…However, as the interrogation arms elongated, the larger size disparity between the Raman laser and the interrogation arms make it more difficult to improve alignment precision when transiting from the two symmetric R-B inter-ferometers with two pairs of Raman beams to one M-Z interferometer with three pairs of Raman beams [9,18]. Compared to the contrast measurement, the phase measurement provides a higher sensitivity [19,25], which is suitable to the precise angular alignment in the four-pulse interferometer. For the symmetric R-B interferometer, the phase imprinted by Raman lasers is written as…”

“…Compared with the contrast, the phase of the R-B interferometer is more sensitive to the angular alignment of separated Raman lasers. It was applied to analyze the systematic error in the four-pulse atom fountain interferometer, where two Raman lasers are aligned at the 0.2 µrad level [19]. While in the M-Z atom interferometer, to align separated Raman lasers, the separated time (T 1 ) should be modulated, which makes the precision for seeking the phase intersected point seriously limited by the cross-coupled parameters including the gravity effect and the velocity dependent crosstalk phase shift [18].…”

Tailoring multi-loop atom interferometers with adjustable momentum transfer

“…with phase shifts ∆Φ (B) and ∆Φ (T) defined in Equations 16,17 and [...] pp denoting the peak-peak variation, and C (B) (C (T) ) being the contrasts of the bottom (top) spurious interferometer. We introduce the mean contrast…”

“…Each pair is retro-reflected by a mirror. The mirrors are parallel to each other to better than 0.2 µrad [17] and tilted by an angle θ 0 = 3.8 • with respect to the horizontal direction x, in order to lift the degeneracy between the ± k eff transitions owing to the Doppler effect. The top collimator can be further inclined by a small adjustable angle ∆θ 20 mrad, leading to a reduced modulus of the effective Raman wave-vector of the top beam, k…”