Dead-Zone-Free Optically Pumped Magnetometer With Small Heading Error

An optically pumped magnetometer (OPM) is presented which is dedicated to sensitive measurements on mobile platforms within the Earth’s magnetic field. It features omnidirectional sensitivity based on amplitude-modulated optical pumping of two cesium vapor cells in perpendicular arrangement. The sensor’s heading error is remarkably suppressed in a differential scheme using two well-balanced circularly polarized laser beams of opposite helicity for each of the cells. In addition, a modulation of the spin-driving frequency eliminates potential systematic errors in sensor read-out due to demodulation phase shifts and instabilities. Within shielded environment, we demonstrate the omnidirectional sensing characteristics, on average a maximum heading error of 0.4 nT for arbitrary sensor orientation, and a noise-limited magnetic flux density resolution of 1.8 pT/ $\surd $ Hz within a sensor 3-dB bandwidth of 1 kHz.