Angular momentum alignment-based magneto-optical signals for the detection of two orthogonal magnetic field components in atomic Cs.

We present a compact magnetometer that is sensitive along two orthogonal magnetic field components using two beams from the same laser source. We implement a pump-probe geometry from LeGal et al [1] where a linearly polarized (E_p) pump beam creates atomic alignment that interacts with the magnetic field (B_z) and the state of the system is probed by a linearly polarized (E_s1) probe beam. The compactness of the method stems from the fact the required angle between the pump (k_p) and probe (k_s) beams is 35.3 degrees which in turn means that the light from both beams can enter the vapour cell from the same optical port. When an external magnetic field (B_z) is applied in a direction perpendicular both to E_p and E_s1 the initially aligned state starts to precess around B_z. Because E_s1 lies in the x-y plane and makes a π/4 angle with respect to the y-axis, the probe beam yields a dispersive dependence of the absorption on the transverse magnetic field component B_z. For the system to be senstive to magnetic field along x-axis (B_x) we rotate the polarization of the probe beam around k_s until the E_s1 lies in the z-y plane. We implement this rotation of the plane of polarization experimentally by the use of an electro-optic modulator. This enables us to detect two orthogonal components of the external magnetic field from a single experiment.

We have performed simulations of the absorption signals for various Cs D1 transitions and studied how the signal is dependent on the Rabi frequency. We have also obtained experimental signals with several combinations of pump and probe beam intensity ratios for all Cs D1 hyperfine transitions.

[1] G. Le Gal, G. Lieb, F. Beato, T. Jager, H. Gilles, and A. Palacios-Laloy, Phys. Rev. Appl. 12, 064010 (2019).