A Portable Ultrasensitive SERF Atomic Magnetometer for Biomagnetic Measurements

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A Portable Ultrasensitive SERF Atomic
Magnetometer for Biomagnetic Measurements

• R Wyllie,1 Z Li,2 R Wakai,3 N Proite,1 P Cook,1 T
  Walker1

1 Department of Physics, UW-Madison 2 Center
for Clinical Neurosciences, UT-Houston Health
Science Center 3 Department of Medical
Physics, UW-Madison
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Requirements for Biomagnetic Measurements

• Sensitivity
• Bandwidth100Hz
• Portability

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Atomic SERF Magnetometer
Note Spin-exchange collisions do not affect G
Romalis et. al., Nature, 422, 596, 2003
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Experimental Concerns

• For full SERF sensitivity, precession rateltltspin
  relaxation rate
• Magnetic shielding, careful nulling using
  Helmholtz coils

• Noise Sources
• Nonmagnetic, technical noise (e.g. vibrations,
  thermal fluctuations, etc.)
• Johnson noise (thermal electron motion)

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Technical Noise from an hot air heated cell scheme
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Z-Mode

• Goal use lock-in technique to extract signal
  from nonmagnetic noise
• Apply a large, oscillating kHz magnetic field in
  z-direction (along pump)
• For best sensitivity, Larmor frequencyparametric
  frequency, sets Bz430nT
• Use lock-in detection of signal
• Two detection directions
• Z1, Sy signal oscillates at wz
• Z2, Sx signal oscillates at 2wz
• Zero transverse fields produce no
  signalbackground free

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Z-Mode Results

• Significantly reduces nonmagnetic noise
• Retains sensitivity and bandwidth of normal SERF
  magnetometer operation

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Current Setup

• Rb 87 with N2 (100T) buffer gases
• Circularly polarized pump at 795nm
• Linearly polarized probe at 780nm
• Cell heated to 180 C

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Technical Improvements

• Plastic, ceramic, and Teflon parts reduce Johnson
  noise, improve portability
• Matched resistive film heaters create little
  magnetic field, allow smaller apparatus, less
  noise (similar to Kitching et al heating scheme)
• RF heating, atoms not affected by high frequency
  (MHz) fields
• Insulation allows subject to be 1cm away from
  cell
• Easy conversion to gradiometer with pump tube

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Adult MCG
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Acknowledgments

• This work funded by a grant from the NIH