A self-oscillating magnetometer based on nonlinear magneto-optical rotationusing amplitude-modulated pump light and unmodulated probe light (AM-NMOR) in87Rb has been constructed and tested towards a goal of airborne detection ofmagnetic anomalies. In AM-NMOR, stroboscopic optical pumping via amplitudemodulation of the pump beam creates alignment of the ground electronic state ofthe rubidium atoms. The Larmor precession causes an ac rotation of thepolarization of a separate probe beam; the polarization rotation frequencyprovides a measure of the magnetic field. An anti-relaxation coating on thewalls of the atomic vapor cell results in a long lifetime of 56 ms for thealignment, which enables precise measurement of the precession frequency. Lightis delivered to the magnetometer by polarization-maintaining optical fibers.Tests of the sensitivity include directly measuring the beat frequency betweenthe magnetometer and a commercial instrument and measurements of Earth's fieldunder magnetically quiet conditions, indicating a sensitivity of at least 5pT/\sqrt{Hz}. Rotating the sensor indicates a heading error of less than 1 nT,limited in part by residual magnetism of the sensor.
展开▼
