Parametric modulation of an atomic magnetometer

Li, Zhimin; Wakai, Ronald T.; Walker, Thad

doi:10.1063/1.2357553

Cited by 98 publications

(57 citation statements)

References 10 publications

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“…In practical situations, significant 1/f noise may arise due to external elements, such as laser fluctuations caused by air currents. Such noise may be reduced using spin modulation techniques [47].…”

Section: Additional Characteristics Of a Magnetometermentioning

confidence: 99%

Optical magnetometry

2007

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Some of the most sensitive methods of measuring magnetic fields utilize interactions of resonant light with atomic vapor. Recent developments in this vibrant field are improving magnetometers in many traditional areas such as measurement of geomagnetic anomalies and magnetic fields in space, and are opening the door to new ones, including, dynamical measurements of bio-magnetic fields, detection of nuclear magnetic resonance (NMR), magnetic-resonance imaging (MRI), inertialrotation sensing, magnetic microscopy with cold atoms, and tests of fundamental symmetries of Nature.

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Section: Additional Characteristics Of a Magnetometermentioning

confidence: 99%

Optical magnetometry

2007

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“…When the field parallel to the pump beam B z corresponds to a Larmor frequency greater than the atomic relaxation rate, the magnetometer also has a significant resonant response to the field B x parallel to the probe beam; the response in this regime is comparable in magnitude to the response to B y . 8 Thus, the measured noise spectrum V m (f ) is composed of the magnetometer response to noise in both x and y directions and can be calibrated using…”

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confidence: 99%

A low-noise ferrite magnetic shield

Kornack

Smullin

Lee

et al. 2007

Applied Physics Letters

202

128

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Ferrite materials provide magnetic shielding performance similar to commonly used high permeability metals but have lower intrinsic magnetic noise generated by thermal Johnson currents due to their high electrical resistivity. Measurements inside a ferrite shield with a spin-exchange relaxationfree (SERF) atomic magnetometer reveal a noise level of 0.75 fT Hz −1/2 , 25 times lower than would be expected in a comparable µ-metal shield. We identify a 1/f component of the magnetic noise due to magnetization fluctuations and derive general relationships for the Johnson current noise and magnetization noise in cylindrical ferromagnetic shields in terms of their conductivity and complex magnetic permeability.PACS numbers: 07.55. Ge, 07.55.Nk, 33.35.+r Many sensitive magnetic measurements depend on high performance magnetic shields typically made from high magnetic permeability metals.1 Several layers of such µ-metal can attenuate external fields by many orders of magnitude. The most sensitive measurements, however, are limited at the level of 1-10 fT Hz −1/2 by the magnetic noise generated by the innermost layer of the magnetic shield itself.2,3 Superconducting magnetic shields do not generate magnetic noise, 4 but thermal radiation shields required for their use with roomtemperature samples typically also generate noise of 1-3 fT Hz −1/2 . MnZn ferrites are promising materials for magnetic shielding because of their high relative permeability (µ ∼ 10 4 µ 0 ) and much higher electrical resistivity (ρ ∼ 1 Ω m) than µ-metal. We measured magnetic fields inside a 10 cm diameter MnZn ferrite shield using a spin-exchange relaxation free (SERF) atomic magnetometer and found that the magnetic noise level is up to 10 times lower than the noise measured in Ref. 3 from a 40 cm diameter µ-metal shield. In addition to electrical resistivity other sources of dissipation can lead to magnetic noise in accordance with fluctuation-dissipation theorem. In particular, magnetic viscosity effects result in an imaginary component of magnetic permeability at low frequency and generate magnetization noise with a 1/f power spectrum.5 The measured low frequency magnetic noise inside the ferrite is in good agreement with a prediction for this magnetization noise based on independently measured complex permeability of the ferrite material. To aid with the design of low noise magnetic shields we also derive simple analytic relationships for Johnson current noise and magnetization noise inside infinitely long cylindrical magnetic shields.Shield performance was measured using a SERF magnetometer, diagrammed in Fig.

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“…This limits the sensitivity of the SERF magnetometer at the lower frequency. Li et al previously demonstrated a SERF magnetometer using parametric modulation to suppress nonmagnetic technical noise, but laser intensity fluctuation was not suppressed [14]. To date, a SERF magnetometer suppressing laser intensity noise and thermal noise simultaneously has not been reported.…”

Section: Introductionmentioning

confidence: 97%

Spin-exchange relaxation-free magnetic gradiometer with dual-beam and closed-loop Faraday modulation

et al. 2014

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Spin-exchange relaxation-free (SERF) atomic magnetometers usually adopt Faraday modulation to achieve better performance but suffer from laser intensity noise, thermal noise generated by the Faraday modulator, and nonmagnetic technical noise. These noises limit the sensitivity of the SERF magnetometer. We demonstrate a SERF magnetic gradiometer with dual-beam and closed-loop Faraday modulation. Operating in the SERF regime, the gradiometer utilizes an additional Faraday modulator rotation feedback to suppress probe laser intensity noise and thermal noise associated with the Faraday modulator, and it simultaneously uses dual-beam difference to cancel common-mode nonmagnetic technical noises. A gradient sensitivity of 14 fT∕Hz 1∕2 per 1 cm gradiometer base length was achieved using Cs atoms.

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Parametric modulation of an atomic magnetometer

Cited by 98 publications

References 10 publications

Optical magnetometry

Optical magnetometry

A low-noise ferrite magnetic shield

Spin-exchange relaxation-free magnetic gradiometer with dual-beam and closed-loop Faraday modulation

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