Active Magnetic-Field Stabilization with Atomic Magnetometer

Abstract

A magnetically-quiet environment is important for detecting faint magnetic-field signals or nonmagnetic spin-dependent interactions. Passive magnetic shielding using layers of large magnetic-permeability materials is widely used to reduce the magnetic-field noise. The magnetic-field noise can also be actively monitored with magnetometers and then compensated, acting as a complementary method to the passive shielding. We present here a general model to quantitatively depict and optimize the performance of active magnetic-field stabilization and experimentally verify our model using optically-pumped atomic magnetometers. We experimentally demonstrate a magnetic-field noise rejection ratio of larger than ∼800 at low frequencies and an environment with a magnetic-field noise floor of ∼40 fT/Hz1/2 in unshielded Earth’s field. The proposed model provides a general guidance on analyzing and improving the performance of active magnetic-field stabilization with magnetometers. This work offers the possibility of sensitive detections of magnetic-field signals in a variety of unshielded natural environments.

Frequency Response of Optically Pumped Magnetometer with Nonlinear Zeeman Effect

“…Full and precise knowledge of the frequency response of the OPM can help to automatically optimize parameters of the closed-loop operation of the OPM and thus help to extend the bandwidth of the OPM without losing its sensitivity, or to improve the identity between the frequency responses of different OPMs to improve the noise rejection ratio of the gradiometer [26]. As closed-loop magnetic-noise-compensation setups require adequate knowledge of the system response, our work can also help to improve the performance of the active magnetic-field stabilization operated in the Earth's field [29,37] which is attractive for ultralow-field nuclear magnetic resonance [7] and for recording bio-magnetic signals from human brain activities in unshielded environments [26,38].…”

“…We find that the frequency response of alkali atoms based OPM is also influenced by the NLZ effect. Full and precise knowledge about the OPM's frequency response is important for parameter adjusting in control systems that involve the OPM, such as the closed-loop operation of the OPM [28], or the magnetic-field stabilization with OPM [29]. In the case of a small amplitude of the magnetic field, the NLZ effect is much smaller than the magnetic resonance linewidth and the frequency response of the OPM is typically a first-order Butterworth low-pass filter [28,30].…”

Spin dynamic response to a time dependent field

“…Both the extended flat gain ( ≈ Γ∕2 ) and the extended flat phase ( ≈ Γ ) conditions can be of interest in magnetometric applications, e.g. in the detection of magnetic signals with spectral components which range from zero to (about) Γ or when the magnetometric signal is used to feed a closed-loop system for active field stabilization [52,53].…”

VCSEL frequency stabilization for optically pumped magnetometers

“…The intensity noise spectral density (NSD) is calculated under the free-running and single-closed-loop modes. Subsequently, the noise rejection ratio (NRR) is introduced to represent the noise suppression effect [29] :…”