Sensitive magnetometry based on nonlinear magneto-optical rotation

TLDR

The study investigates applying nonlinear magneto‑optical Faraday rotation to magnetometry and explores its shot‑noise‑limited sensitivity to sub‑µG magnetic fields near the D1 and D2 lines of 85Rb, showing it can reach 3×10⁻¹² G/√Hz. The authors use a modulation polarimeter to measure Faraday rotation of a laser resonant with Rb transitions, with the Rb vapor confined in an evacuated cell coated to preserve ground‑state polarization over thousands of wall collisions. The technique yields ultranarrow (~10⁻⁶ G) magnetic‑field‑dependent optical‑rotation features and demonstrates shot‑noise‑limited sensitivity down to 3×10⁻¹² G/√Hz for sub‑µG fields.

Abstract

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 $(\ensuremath{\sim}{10}^{\ensuremath{-}6} \mathrm{G})$ in the magnetic-field dependence of optical rotation. The potential sensitivity of this scheme to sub-$\ensuremath{\mu}\mathrm{G}$ magnetic fields as a function of atomic density, light intensity, and light frequency is investigated near the $D1$ and $D2$ 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 $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12} \mathrm{G}/\sqrt{\mathrm{Hz}}.$