We present first, encouraging results obtained with an experimental apparatus based on Coherent Population Trapping and aimed at detecting biological (cardiac) magnetic field in magnetically compensated, but unshielded volume. The work includes magnetic-field and magnetic-field-gradient compensation and uses differential detection for cancellation of (common mode) magnetic noise. Synchronous data acquisition with a reference (electro-cardiographic or pulse-oximetric) signal allows for improving the S/N in an off-line averaging. The set-up has the relevant advantages of working at room temperature with a small-size head, and of allowing for fast adjustments of the dc bias magnetic field, which results in making the sensor suitable for detecting the bio-magnetic signal at any orientation with respect to the heart axis and in any position around the patient chest, which is not the case with other kinds of magnetometers.
A multi-channel atomic magnetometer operating in an unshielded environment is described and characterised. The magnetometer is based on D1 optical pumping and D2 polarimetry of Cs vapour contained in gas-buffered cells. Several technical implementations are described and discussed in detail. The demonstrated sensitivity of the setup is 100fT/Hz^1/2 when operating in the difference mode.
We present experimental data and theoretical interpretation of NMR spectra of remotely magnetized samples, detected in an unshielded environment by means of a differential atomic magnetometer. The measurements are performed in an ultra-low-field at an intermediate regime, where the J-coupling and the Zeeman energies have comparable values and produce rather complex line sets, which are satisfactorily interpreted.
We report on a single-channel rubidium radio-frequency atomic magnetometer operating in un-shielded environments and near room temperature with a measured sensitivity of 130 fT/\sqrt{Hz}. We demonstrate consistent, narrow-bandwidth operation across the kHz - MHz band, corresponding to three orders of magnitude of magnetic field amplitude. A compensation coil system controlled by a feedback loop actively and automatically stabilizes the magnetic field around the sensor. We measure a reduction of the 50 Hz noise contribution by an order of magnitude. The small effective sensor volume, 57 mm^3, i…
Progress in electromagnetic induction imaging with atomic magnetometers has brought its domain to the edge of the regime useful for biomedical imaging. However, a demonstration of imaging below the required 1 Sm$^{-1}$ level is still missing. In this Letter, we use an $^{87}$Rb radio-frequency atomic magnetometer operating near room temperature in an unshielded environment to image calibrated solutions mimicking the electric conductivity of live tissues. By combining the recently introduced near-resonant imaging technique with a dual radio-frequency coil excitation scheme, we image 5 mL of sol…
We report on a compact, tunable, and scalable to large arrays imaging device, based on a radio-frequency optically pumped atomic magnetometer operating in magnetic induction tomography modality. Imaging of conductive objects is performed at room temperature, in an unshielded environment and without background subtraction. Conductivity maps of target objects exhibit not only excellent performance in terms of shape reconstruction but also demonstrate detection of sub-millimetric cracks and penetration of conductive barriers. The results presented here demonstrate the potential of a future genera…
本文报道了一种基于非线性磁光旋转效应的双通道磁强计。Cs原子被光学泵浦，并由调谐到D $_2$线的自由运行二极管激光器探测。泵浦激光器的宽频率调制用于产生同步塞曼光泵浦和超精细再泵浦。该磁力计工作在无屏蔽环境中，通过差分测量的方法消除了远距离磁源的杂散信号。在这种情况下，磁力计同时给出磁场模量和场差。共模噪声抑制允许灵敏度为\pthz{2}的高分辨率磁力测量。这种灵敏度与长期稳定性和大带宽相结合，使得可以在5 cm $^3$的测量体积中检测水质子磁化及其自由感应衰减
We demonstrate remote detection of rotating machinery, using an atomic magnetometer at room temperature and in an unshielded environment. The system relies on the coupling of the AC magnetic signature of the target with the spin-polarized, precessing atomic vapor of a radio-frequency optical atomic magnetometer. The AC magnetic signatures of rotating equipment or electric motors appear as sidebands in the power spectrum of the atomic sensor, which can be tuned to avoid noisy bands that would otherwise hamper detection. A portable apparatus is implemented and experimentally tested. Proof-of-con…
We present a single-beam atomic magnetometer operating at room temperature for the measurement of ac magnetic fields. The magnetometer functions in the non-linear regime of magneto-optical rotation of $^{85}$Rb atomic vapour. We demonstrate a sensitivity of $\sim 0.9$ pT$/ \sqrt{Hz}$ at 2 kHz and a large bandwidth of 24 kHz. The dynamic range of measurement is $10^6$, making the sensor effective even in Earth's field. We present the signal-to-noise and bandwidth characteristics of the system for both shielded and unshielded modes of operation. Moreover, we perform theoretical analysis for the …
We show that a single atomic magnetometer in a magnetically unshielded environment can be used to perform magnetic particle spectroscopy (MPS) and AC susceptometry (ACS) on liquid-suspended magnetic nanoparticles. We demonstrate methods allowing a simultaneous recording of M(H) and dM/dH(H) dependences of samples containing down to 1 $μ$g of iron. Our results pave the way towards an atomic magnetometer based MPI scanner.
We demonstrate electromagnetic induction imaging with an unshielded, portable radio-frequency atomic magnetometer scanning over the target object. This configuration satisfies standard requirements in typical applications, from security screening to medical imaging. The ability to scan the magnetometer over the object relies on the miniaturization of the sensor head and on the active compensation of the ambient magnetic field. Additionally, a procedure is implemented to extract high-quality images from the recorded spatial dependent magnetic resonance. The procedure is shown to be effective in…
The sensitive detection of either static or radio-frequency \textsc{(rf)} magnetic fields is essential to many fundamental studies and applications. Here, we demonstrate the operation of a cold-atom-based, \textsc{rf} magnetometer in performing {1-D and 2-D imaging} of small metallic objects. It is based on a cold $^{85}$Rb atomic sample, and operates in an unshielded environment with no active field stabilization. It shows a sensitivity up to $200\, \rm{pT}/\sqrt{\rm Hz}$ in the $5-35\, \rm{kHz}$ range bandwidth and can resolve a cut $0.4\, \rm{mm}$ wide in a $0.8\, \rm{mm}$ thick metallic fo…
We demonstrate a portable all-optical intrinsic scalar magnetic gradiometer composed of miniaturized cesium vapor cells and vertical-cavity surface-emitting lasers (VCSELs). Two cells, with an inner dimension of 5 mm x 5 mm x 5 mm and separated by a baseline of 5 cm, are driven by one VCSEL and the resulting Larmor precessions are probed by a second VCSEL through optical rotation. The off-resonant linearly polarized probe light interrogates two cells at the same time and the output of the intrinsic gradiometer is proportional to the magnetic field gradient measured over the given baseline. Thi…
We present a portable optically pumped magnetometer instrument for ultra-sensitive measurements within the Earth's magnetic field. The central part of the system is a sensor head operating a MEMS-based Cs vapor cell in the light-shift dispersed Mz mode. It is connected to a compact, battery-driven electronics module by a flexible cable. We briefly review the working principles of the device and detail on the realization of both, sensor head and electronics. We show shielded and unshielded measurements within a static magnetic field amplitude of 50 uT demonstrating a noise level of the sensor s…
Optically pumped atomic magnetometers (OPMs) offer highly sensitive magnetic measurements using compact hardware, offering new possibilities for practical precision sensors. Double-resonance OPM operation is well suited to unshielded magnetometry, due to high sensor dynamic range. However, sensor response is highly anisotropic with variation in the orientation of the magnetic field. We present data quantifying these effects and discuss implications for the design of practical sensors.
Double-resonance optically pumped magnetometers are an attractive instrument for unshielded magnetic field measurements due to their wide dynamic range and high sensitivity. Use of linearly polarised pump light creates alignment in the atomic sample, which evolves in the local static magnetic field, and is driven by a resonant applied field perturbation, modulating the polarisation of transmitted light. We show for the first time that the amplitude and phase of observed first- and second-harmonic components in the transmitted polarisation signal contain sufficient information to measure static…
We report on the use of radio-frequency optical atomic magnetometers for magnetic induction tomography measurements. We demonstrate the imaging of dummy targets of varying conductivities placed in the proximity of the sensor, in an unshielded environment at room-temperature and without background subtraction. The images produced by the system accurately reproduce the characteristics of the actual objects. Furthermore, we perform finite element simulations in order to assess the potential for measuring low-conductivity biological tissues with our system. Our results demonstrate the feasibility …
We describe a method to dispersively detect all three vector components of an external magnetic field using alkali atoms based on the Voigt effect. Our method relies on measuring the linear birefringence of the radio frequency dressed atomic medium via polarization homodyning. This gives rise to modulated polarization signals at the first and second harmonic of the dressing frequency. The vector components of the external magnetic field are mapped onto the quadratures of these harmonics. We find that our scheme can be utilised in both cold and hot atomic gases to detect such external fields in…
Portable Single-Beam Atomic Total-Field Magnetometer for Stand-off Magnetic Sensing
OAQ Co. Ltd.（OAQ有限公司）；Department of Physics, Korea Advanced Institute of Science and Technology（韩国科学技术院物理系）；Graduate School of Data Science, Pusan National University（釜山国立大学数据科学研究生院）
We present NMR spectra of remote-magnetized deuterated water, detected in an unshielded environment by means of a differential atomic magnetometer. The measurements are performed in a $μ$T field, while pulsed techniques are applied -following the sample displacement- in a 100~$μ$T field, to tip both D and H nuclei by controllable amounts. The broadband nature of the detection system enables simultaneous detection of the two signals and accurate evaluation of their decay times. The outcomes of the experiment demonstrate the potential of ultra-low-field NMR spectroscopy in important applications…
We describe a novel pulsed magnetic gradiometer based on the optical interference of sidebands generated using two spatially separated alkali vapor cells. The sidebands are produced with high efficiency using parametric frequency conversion of a probe beam interacting with $^{87}$Rb atoms in a coherent superposition of magnetically sensitive hyperfine ground states. Interference between the sidebands generates a low-frequency beat note whose frequency is determined by the magnetic field gradient between the two vapor cells. In contrast to traditional magnetic gradiometers, our approach provide…
We present a method of optical magnetometry with parts-per-billion resolution that is able to detect biomagnetic signals generated from the human brain and heart in Earth's ambient environment. Our magnetically silent sensors measure the total magnetic field by detecting the free-precession frequency of highly spin-polarized alkali metal vapor. A first-order gradiometer is formed from two magnetometers that are separated by a 3 cm baseline. Our gradiometer operates from a laptop consuming 5 W over a USB port, enabled by state-of-the-art micro-fabricated alkali vapor cells, advanced thermal ins…
