Sensitive magnetometry based on nonlinear magneto-optical rotation

Application of nonlinear magneto-optical (Faraday) rotation to magnetometry is investigated. Our experimental setup consists of a modulation polarimeter that measures rotation of the polarization plane of a laser beam resonant with transitions in Rb. Rb vapor is contained in an evacuated cell with antirelaxation coating that enables atomic ground-state polarization to survive many thousand wall collisions. This leads to ultranarrow features $\left(\sim {10}^{-6}\hspace{0.5em}\mathrm{G}\right)$ in the magnetic-field dependence of optical rotation. The potential sensitivity of this scheme to sub-$\mu \mathrm{G}$ magnetic fields as a function of atomic density, light intensity, and light frequency is investigated near the $D1\mathrm{}$ and $D2\mathrm{}$ lines of ${}^{85}\mathrm{Rb}.$ It is shown that through an appropriate choice of parameters the shot-noise-limited sensitivity to small magnetic fields can reach $3\times {10}^{-12}\hspace{0.5em}\mathrm{G}/\sqrt{\mathrm{Hz}}.$