Multichannel optical atomic magnetometer operating in unshielded environment

Bevilacqua, Giuseppe; Biancalana, Valerio; Chessa, P.; Dancheva, Yordanka

doi:10.1007/s00340-016-6375-2

Cited by 55 publications

(68 citation statements)

References 38 publications

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“…The setup could then be simplified and its footprint reduced by using the same PM fiber for the probe and the pump beams. The necessary polarizations could be created with a multiorder wave plate, and with the pump beam blocked by an interference filter [6,24]. Alternatively, a single laser could be used as pump and probe, where the frequency and polarization of the laser are modulated simultaneously in such a way that it serves as the pump during the first short part of the cycle and as the probe for the rest.…”

Section: Resultsmentioning

confidence: 99%

“…While this would limit the performance of magnetometers, much of this noise can be suppressed using multiple sensors in a gradiometer configuration [23,24]. Therefore, when operated in noisy environments, smaller magnetometer size and better sensitivity can allow for gradiometers with shorter baselines.…”

Section: Introductionmentioning

confidence: 99%

“…In pulsed operation and using quantum nondemolition measurement, a scalar gradiometer sensitivity of 0.54 fT/Hz 1/2 has been experimentally demonstrated with multipass cells in a sensitive volume of 350 mm 3 [26]. Under continuous operation, several groups have shown sensitivities below 1 pT/Hz 1/2 in centimeter-size cells [24,27–30]. Microfabricated scalar sensors have reached sensitivities of 5 pT/Hz 1/2 in a volume of 2 mm 3 with a bandwidth of 1 kHz [31].…”

Section: Introductionmentioning

confidence: 99%

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Pulsed operation of a miniature scalar optically pumped magnetometer

2017

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A scalar magnetic field sensor based on a millimeter-size 87Rb vapor cell is described. The magnetometer uses nearly copropagating pump and probe laser beams, amplitude modulation of the pump beam, and detection through monitoring the polarization rotation of the detuned probe beam. The circularly polarized pump laser resonantly drives a spin precession in the alkali atoms at the Larmor frequency. A modulation signal on the probe laser polarization is detected with a lock-in amplifier. Since the Larmor precession is driven all-optically, potential cross talk between sensors is minimized. And since the pump light is turned off during most of the precession cycle, large offsets of the resonance, typically present in a single-beam Bell–Bloom scheme, are avoided. At the same time, relatively high sensitivities can be reached even in millimeter-size vapor cells: The magnetometer achieves a sensitivity of 1 pT/Hz1/2 in a sensitive volume of 16 mm3, limited by environmental noise. When a gradiometer configuration is used to cancel the environmental noise, the magnetometer sensitivity reaches 300 fT/Hz1/2. We systematically study the dependence of the magnetometer performance on the optical duty cycles of the pump light and find that better performance is achieved with shorter duty cycles, with the highest values measured at 1.25% duty cycle.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Pulsed operation of a miniature scalar optically pumped magnetometer

2017

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“…In practical applications in an unshielded environment, the output noise of scalar magnetometers is often dominated by the background field fluctuation, instead of their fundamental sensitivities. To overcome this problem, a common solution is to set up a gradiometer system using two or more magnetometers [12,13,14]. By taking the reading difference between adjacent magnetometers, this conventional gradiometer configuration suppresses the common field fluctuations at the cost of worsening the fundamental sensitivity by at least a factor of √2, compared with that of an individual magnetometer.…”

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confidence: 99%

Portable intrinsic gradiometer for ultra-sensitive detection of magnetic gradient in unshielded environment

Zhang¹,

Mhaskar²,

Smith³

et al. 2020

Applied Physics Letters

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We demonstrate a portable intrinsic scalar magnetic gradiometer composed of miniaturized cesium vapor cells and verticalcavity surface-emitting lasers (VCSELs). Two cells, with an inner dimension of 5 mm x 5 mm x 5 mm and separated by 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 directly reads out the amplitude difference between magnetic fields at two cell locations. The intrinsic gradiometer scheme has the advantage of avoiding added noise from combining two scalar magnetometers. We achieve better than 18 fT/cm/√Hz sensitivity in the gradient measurement. Ultra-sensitive short-baseline magnetic gradiometers can potentially play an important role in many practical applications, such as nondestructive evaluation and unexplode ordnance (UXO) detection. Another application of the gradiometer is for magnetocardiography (MCG) in an unshielded environment. Real-time MCG signals can be extracted from the raw gradiometer readings. The intrinsic gradiometer greatly simplifies the MCG setup and may lead to ubiquitous MCG measurement in the future.Over the last two decades, many breakthroughs have been achieved in atomic magnetometer research. For example, the discovery of the spin-exchange relaxation-free (SERF) phenomenon at high atomic density and low magnetic field leads to a great improvement in the magnetometer noise performance [1]. Sensitivities comparable with [2] or even outperforming [3] those of superconducting quantum interference devices (SQUIDs) have been reported with SERF magnetometers. Another example is the successful fabrication of atomic magnetometers using the technique of Micro-Electro-Mechanical Systems (MEMS) [4,5,6,7,8]. MEMS techniques enable chip-scale devices, significantly reducing size and power-consumption of atomic magnetometers. Chip-scale magnetometers can have sizes approaching 10 mm 3 and dissipate less than 200 mW. Despite all these advances, applications of atomic magnetometers are still limited. Highly sensitive SERF magnetometers require a magnetically shielded environment while chip-scale total-field magnetometers have subpar noise performances [5], although a scalar magnetometer with a sensitivity of 100 fT/√Hz has been demonstrated using a MEMS-based cesium vapor cell [9]. With bigger cells, scalar magnetometers can reach sensitivities of sub-10 fT/√Hz [10] or even sub-fT/√Hz [11]. In practical applications in an unshielded environment, the output noise of scalar magnetometers is often dominated by the background field fluctuation, instead of their fundamental sensitivities. To overcome this problem, a common solution is to set up a gradiometer system using two or more magnetometers [12,13,14]. By taking the reading difference between adjacent magnetometers, this conventional gradiometer configuration suppresses the common field fluctuations at the cost of worsening the fundamental sensitivity by at least a factor...

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“…In most of in-situ ULF-NMR experimental setups, in-situ premagnetization can be performed only with hyperpolarization techniques [9][10][11] , due to incompatibility of magnetic shields with strong magnetic fields, so that Zeeman-interaction polarization with fields exceeding 50-100 mT is relegated to exsitu (remote detection) apparatuses 12 . This is not the case of our setup, which is designed and optimized to operate in unshielded environment, and uses active field-compensation 13 and differential-measurement techniques 14 to reject disturbances produced by external sources, while other experiments in shielded volumes use typically weaker (10-20 mT) premagnetization fields 15 .…”

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confidence: 99%

Fast switching coil system for sample premagnetization in an unshielded ultra-low-field nuclear magnetic resonance experiment

Biancalana

Cecchi

Stiaccini

et al. 2020

Review of Scientific Instruments

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We present a system developed to premagnetize liquid samples in an ultra-low-field Nuclear Magnetic Resonance (NMR) experiment. Liquid samples of a few milliliter are exposed to a magnetic field of about 70 mT, which is abruptely switched off, so to leave a transverse microtesla field where nuclei start precessing. An accurate characterization of the transients and intermediate field level enables a reliable operation of the detection system, which is based on an optical magnetometer.The ultra-low-field (ULF) regime in Nuclear Magnetic Resonance (NMR) experiments 1 corresponds to precession field intensities ranging around the microtesla level, where the nuclear precession is so slow to make the usual detection approaches -based on Faraday induction phenomenon-inadequate or unfeasible. Instead, non-inductive, highly sensitive detectors can be used, such as SQUIDs and optical atomic magnetometers 2 .Optical magnetometers are acknowledged for their practicality (they operate at room temperature) and robustness, making them eligible as high-performance sensors in on-field applications, such as in tomography in hostile environment 3 and material characterization 4 .Optical magnetometers designed to operate in a weak field, can tolerate much stronger (e.g. tesla level) ones, and recover immediately their operativity, as soon as the weak (e.g. microtesla) field is restored. In ultra-low-field NMR, this is the case when the sample is premagnetized in the same position where the nuclear precession is detected. Such in situ magnetization constitutes an approach complementary to remotedetection techniques, where the sample is premagnetized by a strong field in a region at some distance from the sensors and is subsequently shuttled to the weak field region, in the proximity of the sensor that detects the nuclear precession.This note describes an arrangement that makes possible to perform in situ magnetization in a setup previously developed to register NMR 5,6 and MRI 7,8 signals with a remotedetection scheme.

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Multichannel optical atomic magnetometer operating in unshielded environment

Cited by 55 publications

References 38 publications

Pulsed operation of a miniature scalar optically pumped magnetometer

Pulsed operation of a miniature scalar optically pumped magnetometer

Portable intrinsic gradiometer for ultra-sensitive detection of magnetic gradient in unshielded environment

Fast switching coil system for sample premagnetization in an unshielded ultra-low-field nuclear magnetic resonance experiment

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