Magneto-optical signals in a caesium vapour cells can be used for extremely precise magnetic field measurement in 3D [1]. We present experimental results based on angular momentum alignment precession in atomic caesium. The linearly polarized pump beam passing through the cell in the direction $k_p$ creates an aligned state in caesium ground state along $E_p$. As an external magnetic field is applied ($B_x$ or $B_y$), the distribution of angular momentum precesses about the applied field axis. This change in the distribution of angular momentum can be probed by low-intensity linearly polarized ($E_x$ or $E_y$) probe beam with its polarization at a 45 degree angle with respect to the pump beam polarization ($E_p$) and in a plane perpendicular to the applied magnetic field. This pump-probe geometry (see Fig. 1 (a)) is based on [2]. The probe beam transmission signals show strong dispersion-like dependence on the applied magnetic field when the pump beam is on.
The dependence of transmission signals on pump beam intensity and laser frequency as well as beam diameter was studied. We found that the shape of the transmission signal also has strong dependence on the probe beam intensity (see Fig. 1 (b)) as it perturbs the aligned state created by the pump beam. Nevertheless, the experimental results are in agreement with the numerically simulated signals.
