27 research outputs found
Free-induction-decay magnetometer based on a microfabricated Cs vapor cell
We describe an optically pumped Cs magnetometer containing a 1.5 mm thick microfabricated vapor cell with nitrogen buffer gas operating in a free-induction-decay (FID) configuration. This allows us to monitor the free Larmor precession of the spin coherent Cs atoms by separating the pump and probe phases in the time domain. A single light pulse can sufficiently polarize the atomic sample however, synchronous modulation of the light field actively drives the precession and maximizes the induced spin coherence. Both amplitude and frequency modulation have been implemented with noise floors of 3 pT / â Hz and 16 pT / â Hz respectively within the Nyquist limited bandwidth of 500 Hz
How to build a magnetometer with thermal atomic vapor: A tutorial
This article is designed as a step-by-step guide to optically pumped
magnetometers based on alkali atomic vapor cells. We begin with a general
introduction to atomic magneto-optical response, as well as expected
magnetometer performance merits and how they are affected by main sources of
noise. This is followed by a brief comparison of different magnetometer
realizations and an overview of current research, with the aim of helping
readers to identify the most suitable magnetometer type for specific
applications. Next, we discuss some practical considerations for experimental
implementations, using the case of an magnetometer as an example of the
design process. Finally, an interactive workbook with real magnetometer data is
provided to illustrate magnetometer-performance analysis.Comment: 52 pages, 9 figures, 3 tables. Submitted to New Journal of Physics as
an invited review/tutorial for the special issue "Focus on Hot Atomic
Vapors". Minor content and language errors corrected in v
Study and Realization of a Miniature Isotropic Helium Magnetometer
No abstract available.Pas de résumé disponibl
Ultimate parameters of an all-optical MX resonance in Cs in ultra-weak magnetic field
We present the results of studying the parameters of the magnetic MX
resonance in an all-optical sensor built according to the two-beam Bell-Bloom
scheme in nonzero ultra-weak magnetic fields in which the effects of
spin-exchange broadening suppression are partially manifested. We report on the
features of the resonance under these conditions. We also optimize the
resonance parameters to achieve maximum sensitivity in magnetoencephalographic
sensors. We demonstrate an improvement in the ultimate achievable sensitivity
of an all-optical MX sensor by a factor of four or more, which in our
experiment corresponds to a decrease from 13 to 3 fT/Hz1/2 in a volume of 0.13
cm3. We also report the effect of incomplete suppression of spin-exchange
broadening under conditions of strong transverse modulated optical pumping, and
propose a semi-empirical model to describe it
Chip-scale atomic magnetometer based on free-induction-decay
This thesis describes the implementation of an optically pumped caesium magnetometer containing a 1:5mm thick microfabricated vapour cell with nitrogen buffer gas, operating in a free-induction-decay configuration. This allows us to monitor the free Larmor precession of the spin coherent Cs atoms by separating the pump and probe phases in the time domain. A single light pulse can sufficiently polarise the atomic sample;however, synchronous modulation of the light field actively drives the precession and maximises the induced spin coherence. Both amplitude- and frequency-modulation have been adopted producing noise floors of 3.4 pT / âHz and 15.6 pT/âHz, respectively,within a Nyquist limited bandwidth of 500 Hz in a bias field comparable to the Earth's (~50 ÎŒT). We investigate the magnetometers capability in reproducing time-varying magnetic signals under these conditions, including the reconstruction of a 100 pT perturbation using signal averaging.Additionally, we discuss a novel detection mode based on free-induction-decay that observes the spin precession dynamics in-the-dark using Ramsey-like pulses. This aids in suppressing the systematic effects originating from the light-atom interaction during readout, thus vastly improving the accuracy of the magnetometer whilst maintaining a sensitivity that is competitive with previous implementations. This detection technique was implemented further to measure the spin relaxation properties intrinsic to the sensor head, useful in determining the optimal buffer pressure that extends the spin lifetime and improves the sensor's sensitivity performance.This thesis describes the implementation of an optically pumped caesium magnetometer containing a 1:5mm thick microfabricated vapour cell with nitrogen buffer gas, operating in a free-induction-decay configuration. This allows us to monitor the free Larmor precession of the spin coherent Cs atoms by separating the pump and probe phases in the time domain. A single light pulse can sufficiently polarise the atomic sample;however, synchronous modulation of the light field actively drives the precession and maximises the induced spin coherence. Both amplitude- and frequency-modulation have been adopted producing noise floors of 3.4 pT / âHz and 15.6 pT/âHz, respectively,within a Nyquist limited bandwidth of 500 Hz in a bias field comparable to the Earth's (~50 ÎŒT). We investigate the magnetometers capability in reproducing time-varying magnetic signals under these conditions, including the reconstruction of a 100 pT perturbation using signal averaging.Additionally, we discuss a novel detection mode based on free-induction-decay that observes the spin precession dynamics in-the-dark using Ramsey-like pulses. This aids in suppressing the systematic effects originating from the light-atom interaction during readout, thus vastly improving the accuracy of the magnetometer whilst maintaining a sensitivity that is competitive with previous implementations. This detection technique was implemented further to measure the spin relaxation properties intrinsic to the sensor head, useful in determining the optimal buffer pressure that extends the spin lifetime and improves the sensor's sensitivity performance
Analysis of atomic magnetometry using metasurface optics for balanced polarimetry
Atomic magnetometry is one of the most sensitive field-measurement techniques
for biological, geo-surveying, and navigation applications. An essential
process in atomic magnetometry is measurement of optical polarization rotation
of a near-resonant beam due to its interaction with atomic spins under an
external magnetic field. In this work, we present the design and analysis of a
silicon-metasurface-based polarization beam splitter that have been tailored
for operation in a rubidium magnetometer. The metasurface polarization beam
splitter operates at a wavelength of 795 nm and has a transmission efficiency >
83% and a polarization extinction ratio > 20 dB. We show that these performance
specifications are compatible with magnetometer operation in miniaturized vapor
cells with subpicotesla-level sensitivity and discuss the prospect of realizing
compact, high-sensitivity atomic magnetometers with nanophotonic component
integration
Multichannel optical atomic magnetometer operating in unshielded environment
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.Comment: 9 pages, 5 figures, appearing in Appl.Phys.
Recommended from our members
Pulsed operation of a miniature scalar optically-pumped magnetometer
A scalar magnetic field sensor based on a millimeter-size 87 Rb 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/Hz 1/2 in a sensitive volume of 16 mm 3 , limited by environmental noise. When a gradiometer configuration is used to cancel the environmental noise, the magnetometer sensitivity reaches 300 fT/Hz 1/2 . 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.</p
Recommended from our members
OPM magnetorelaxometry in the presence of a DC bias field
Spatial quantitative information about magnetic nanoparticle (MNP) distributions is a prerequisite for biomedical applications like magnetic hyperthermia and magnetic drug targeting. This information can be gathered by means of magnetorelaxometry (MRX) imaging, where the relaxation of previously aligned MNPâs magnetic moments is measured by sensitive magnetometers and an inverse problem is solved. To remove or minimize the magnetic shielding in which MRX imaging is carried out today, the knowledge of the influence of background magnetic fields on the MNPâs relaxation is a prerequisite. We show MRX measurements using an intensity-modulated optically pumped magnetometer (OPM) in background magnetic fields of up to 100ÎŒT. We show that the relaxation parameters alter or may be intentionally altered significantly by applying static fields parallel or antiparallel to the MNPâs alignment direction. Further, not only the relaxation process of the MNPâs magnetic moments could be measured with OPM, but also their alignment due to the MRX excitation field. © 2020, The Author(s)
Waveform reconstruction with a Cs based free-induction-decay magnetometer
We demonstrate an optically pumped magnetometer (OPM) operated in a free-induction-decay (FID) configuration that is capable of tracking oscillating magnetic signals in the presence of a 50 uT static field. Excellent waveform reconstruction is demonstrated for low frequency modulations with respect to the Nyquist limited bandwidth. A 100 pT oscillation was successfully reconstructed using signal averaging, and an optimum sensitivity of 3.9 pT/sqrt{Hz} was measured from the spectrum of the residuals relative to the sinusoidal fit. The impact of the pump-probe repetition rate and spin depolarization on the frequency response of the sensor is investigated in detail using miniaturized vapor cell technology, with the (-3 dB) bandwidths residing beyond the Nyquist limit in each case. We also discuss technical limitations associated with the magnetometer when exposed to oscillating fields of sufficiently high amplitude or frequency. This is discussed in the context of potential distortions arising in the reproduced signals, induced by frequency-modulation (FM) and aliasing artefacts