Optically pumped magnetometers compatible with large transient magnetic fields

Abstract

Optically pumped magnetometers have seen an increased interest in applications such as magnetoencephalography where extremely small magnetic fields produced in the brain must be distinguished from the large and noisy magnetic background of the world. In environments where magnetic shielding may be weak, optically pumped gradiometers are useful for separating out signals of interest from magnetic interference. We describe magnetic sensors operating in closed-loop mode, whereby a feedback signal is used to continuously keep the atoms in a zero-field environment. This allows for a larger linear operating range of the sensor, reduces the need for frequent re-calibration, increases the common-mode rejection ratio of the gradiometers, and increases the linearity as compared to open-loop measurements. We also discuss a specific application of atomic magnetometers in a weakly shielded environment where large magnetic field pulses are used to stimulate a subject's brain. Atomic magnetometers are uniquely suited to quickly recover and take low-noise measurements to probe the resulting neuronal currents after stimulation events.