Atomic noise spectra in nonlinear magneto-optical rotation in a rubidium vapor

We have studied the noise spectra in a nonlinear magneto-optical rotation experiment in a rubidium vapor. We observed the reduction of noise in the intensity difference of two orthogonally polarized components of the laser beam. The dependence of the noise level on both the frequency and the longitudinal magnetic field has been studied. We found that the optimal condition for the noise reduction is to work around zero longitudinal magnetic field, where the intensity correlation between the two orthogonally polarized components is maximum. Our results can be used to reduce or eliminate the atomic excess noise, therefore improving the sensitivity of nonlinear magneto-optical rotation magnetometers and other atom-optical based applications.