Six-Axis Inertial Sensor Using Cold-Atom Interferometry

We have developed an atom interferometer providing a full inertial base. This device uses two counterpropagating cold-atom clouds that are launched in strongly curved parabolic trajectories. Three single Raman beam pairs, pulsed in time, are successively applied in three orthogonal directions leading to the measurement of the three axis of rotation and acceleration. In this purpose, we introduce a new atom gyroscope using a butterfly geometry. We discuss the present sensitivity and the possible improvements.

Figure 1

Six-axis inertial sensor principle. The atomic clouds are launched on a parabolic trajectory, and interact with the Raman lasers at the top. The four configurations (a)–(d) give access to the 3 rotations and the 3 accelerations. In the three pulses configuration, the Raman beams direction can be horizontal or vertical, creating the interferometer in a horizontal (a) or vertical (b),(c) plane. With a butterfly four-pulse sequence of horizontal beams (d), the rotation ${\Omega }_x$ can be measured.

Figure 2

The orthogonally polarized copropagating Raman beams are tilted with respect to the atom trajectories. They are retroreflected by a mirror through a quarter-wave plate so that the atoms interact with counterpropagating beams at frequency ${\omega }_1$ and ${\omega }_2+\delta \omega$ with ${\omega }_1-{\omega }_2\approx 9.2\mathrm{GHz}$. The detuning $\delta \omega$ compensates for the Doppler shift so that each of the two counterpropagating atom clouds can interact with only one pair of beams. Interferometer areas are shown in the case of a three-pulse interferometer.

Figure 3

Fringes obtained with the two interferometers A and B, for an interrogation time of $2T=60\mathrm{ms}$ and a cycling time of 560 ms without averaging.

Figure 4

Acceleration and rotation signals extracted from the half sum and half difference of the phase shifts of interferometers A and B. To obtain the actual value of the rotation, the phase ${\phi }_l$ has to be taken into account. dc offset on the acceleration signal is due to the residual contribution of gravitational acceleration. The acceleration dispersion on the acceleration signal comes from oscillations of the isolation platform.

Figure 5

Allan standard deviations of acceleration (triangles) and rotation (circles) measurements. Dashed lines corresponds to the $-1/2$ slope expected for a white noise. The peak near 10 s averaging time on the acceleration signal is due to the residual oscillations of the isolation platform tilt.

Figure 6

Fringes obtained with both interferometers A and B in the four-pulses butterfly configuration for a total interrogation time of $2T=60\mathrm{ms}$.