Fast Measurement of Magnetic Gradient Based on Four-Channel Optically Pumped Atomic Magnetometer

Spin-exchange relaxation-free atomic magnetometers have gradually replaced superconducting quantum interference devices in numerous applications owing to the urgent need for miniaturization and portability in biomagnetic measurement research. With the decrease-in intrinsic noise, common-mode noise from the environment has become the dominant noise source. Furthermore, high-accuracy positioning of biomagnetic fields has placed severe demands on the resolution of array-based magnetometers. Gradient magnetometry exhibits significant development potential because it reduces the measurement cross-section and suppresses common-mode noise. However, a single gradiometer can only compensate for the magnetic field in the reference channel. To overcome this limitation, a method for obtaining the distribution of the magnetic gradient across the measurement area by calculating the difference between the precession frequencies at various locations inside the cell was proposed. Moreover, the response amplitude is not involved in the calculation and is also applicable in the case of multi-channel with different responses. The developed approach was verified by applying an artificial gradient field to the measurement area inside the cell, and the feasibility of our methodology was confirmed experimentally.