Sensitive optical atomic magnetometer based on nonlinear magneto-optical rotation

TL;DR

This paper presents a sensitive optical atomic magnetometer based on nonlinear magneto-optical rotation using rubidium atoms, demonstrating high sensitivity suitable for airborne magnetic anomaly detection.

Contribution

The development of a self-oscillating AM-NMOR magnetometer with long atomic alignment lifetime and fiber-optic delivery, achieving high sensitivity and low heading error.

Findings

Sensitivity of at least 5 pT/√Hz achieved

Long atomic alignment lifetime of 56 ms

Heading error less than 1 nT

Abstract

A self-oscillating magnetometer based on nonlinear magneto-optical rotation using amplitude-modulated pump light and unmodulated probe light (AM-NMOR) in 87Rb has been constructed and tested towards a goal of airborne detection of magnetic anomalies. In AM-NMOR, stroboscopic optical pumping via amplitude modulation of the pump beam creates alignment of the ground electronic state of the rubidium atoms. The Larmor precession causes an ac rotation of the polarization of a separate probe beam; the polarization rotation frequency provides a measure of the magnetic field. An anti-relaxation coating on the walls of the atomic vapor cell results in a long lifetime of 56 ms for the alignment, which enables precise measurement of the precession frequency. Light is delivered to the magnetometer by polarization-maintaining optical fibers. Tests of the sensitivity include directly measuring the beat frequency between the magnetometer and a commercial instrument and measurements of Earth's field under magnetically quiet conditions, indicating a sensitivity of at least 5 pT/\sqrt{Hz}. Rotating the sensor indicates a heading error of less than 1 nT, limited in part by residual magnetism of the sensor.