Scalar Magnetometry Below 100 fT/Hz^1/2 in a Microfabricated Cell

Abstract

Zero-field optically-pumped magnetometers are a room-temperature alternative to traditionally used superconducting sensors detecting extremely weak magnetic fields. They offer certain advantages such as small size, flexible arrangement, reduced sensitivity in ambient fields offering the possibility for telemetry. Devices based on microfabricated technology are nowadays commercially available. The limited dynamic range and vector nature of the zero-field magnetometers restricts their use to environments heavily shielded against magnetic noise. Total-field (or scalar) magnetometers based on microfabricated cells have demonstrated subpicotesla sensitivities only recently. This work demonstrates a scalar magnetometer based on a single optical axis, 18 (3 × 3 × 2) mm 3 microfabricated cell, with a noise floor of 70 fT/Hz 1/2 . The magnetometer operates in a large static magnetic field range, and and is based on a simple optical and electronic configuration that allows the development of dense sensor arrays. Different methods of magnetometer interrogation are demonstrated. The features of this magnetic field sensor hold promise for applications of miniature sensors in nonzero field environments such as unshielded magnetoencephalography (MEG) and brain-computer interfaces (BCI).

A study of scalar optically-pumped magnetometers for use in magnetoencephalography without shielding

“…In our experiments, we used a scalar OPM sensor with a noise floor of 70 fT/ √ Hz [27] and measurement bandwidth of 100 Hz. For these OPM parameters, we then varied the dipole strength for simplicity in our simulation.…”

“…We constructed a virtual sensor array based on a single scalar gradiometer using a scalar magnetometer concept described in detail in Ref. [27]. The gradiometer had a fixed base distance and was used to record many dipolar sources spread over a volume consecutively.…”

Pulsed Optically Pumped Magnetometers: Addressing Dead Time and Bandwidth for the Unshielded Magnetorelaxometry of Magnetic Nanoparticles

“…While depending on the operation mode of the OPM, the bandwidth and dynamic range are mostly limited by the linewidth of the resonance, but can be increased by artificially broadening the linewidth (at the expense of losing sensitivity), or by incorporating feedback loops [ 29 ]. While OPM based on the free-precession principle are well known [ 29 , 30 , 31 , 32 , 33 , 34 , 35 ], recently a bandwidth of up to was demonstrated with sensitivity degrading linearly with frequency [ 36 ]. However, in this case the preparation of the atoms is implemented using low power synchronous pumping, which would add to the dead time after switching off the excitation field in MRX.…”

“…However, in this case the preparation of the atoms is implemented using low power synchronous pumping, which would add to the dead time after switching off the excitation field in MRX. Several other techniques can be applied to establish the detectable Larmor precession of the optically pumped atoms: some of those rely on enforcing the optimal magnetic field configuration for optical pumping [ 34 , 35 ], which however would influence the relaxation behavior of the MNP and are therefore not favorable. This can be further refined by short and weak RF pulses to re-orient the polarized spin and ensure maximal spin detection efficiency [ 37 ].…”

A femtotesla quantum-noise-limited pulsed gradiometer at finite fields

“…At lower field of 7.3 µT sub-femtotesla sensitivity has been demonstrated [34] using a gradiometer configuration in a single cm-sized multipass cell. A noise floor of about 100 fT/ √ Hz at 10 µT has been obtained with a microfabricated 18 mm 3 cell [35]. Recent works on intrinsic [36][37][38][39] or synthetic [40] (two spatially separated OPMs) gradiometers reported sensitivity below 50 fT/cm/ √ Hz, enabling the first detection of human biomagnetism by OPMs in ambient environment [40].…”