Background

The extremely high sensitivities of zero-field magnetometers (ZFM) have paved the way towards new applications such as non-cryogenic magnetocardiography (MCG) and magnetoencephalography (MEG). In the last several years, progress has been made towards improving the sensitivity of total-field magnetometers (TFM) that operate in unshielded (Earth’s) magnetic field environment. Their sensitivity is typically lower than that of the ZFM. The TFM offers higher dynamic range and relaxed control of the ambient magnetic fields, and thus can be used in applications incompatible with zero-field operation, such as ultralow-field NMR and magnetic anomaly detection. TFM reach highest sensitivity when they measure the precession of an atomic polarization in a plane perpendicular to the direction of the measured ambient magnetic field. The preparation of the atomic polarization in such a plane difficult, as the ambient magnetic field counteracts the spin preparation done using optical pumping.

Technology Overview

Researchers at the University of Colorado have come up with a new method to increase the efficiency of the atomic polarization preparation by zeroing the ambient magnetic field at the position of a pulsed TFM. Specifically, the existing ambient magnetic field is nulled at the position of the TFM during the preparation phase of the atomic polarization. This is achieved by applying a DC magnetic field in the opposite direction to the ambient one during the preparation of the atomic polarization. The field zeroing increases the efficiency of the atomic polarization preparation through optical pumping.

Additionally, it is known that the free precession of the atomic polarization reacts instantaneously to changes of the ambient magnetic field. This means that the bandwidth of the ambient magnetic field measurement is not limited by the repetition rate of the TFM pump-probe cycle, which is determined by the sum of the pump and probe phase durations. A TFM that uses a pump-probe cycle can thus measure ambient magnetic field dynamics that is faster than the TFM repetition rate. The sensitivity with which the ambient field dynamics is measured is given by the single-cycle sensitivity of the TFM, while the bandwidth exceeds significantly the TFM repetition rate.

Stage of Development

Technology Readiness Level (TRL): 7.

Benefits

Higher TFM sensitivity
Polarization preparation not dependent on ambient magnetic field
Can be optimized to achieve maximum atomic polarization
No need for short-pulse, high-power pumping light, resonant AC or strong DC magnetic field pulses

Applications

Magnetoencephalography
Magnetocardiography
Ultralow-field nuclear magnetic resonance
Magnetic Anomaly Detection, Magnetorelaxometry

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Method for Increasing the Degree of Atomic Polarization in Optically Pumped Atomic Magnetometers based on Magnetic Field Zeroing