Intrinsic radio-frequency gradiometer

An optically pumped magnetic gradiometer for the detection of human biomagnetism

“…Because of the light absorption within the cells, the power of the laser beam decreases after each pass. Additionally, deviation in birefringence after each pass through the waveplate results in further reduction of the signal recorded by cell 1 [38]. Since the amplitude of the NMOR signals depends on the light intensity and polarisation, this results in A 1 ̸ = A 2 , voiding a necessary condition for the correct functioning of the gradiometer.…”

“…This eliminates the need of post-processing and does not degrade the sensor's sensitivity. So far the flip in rotation direction between measurement points in various kinds of OPMG has been achieved either by adding an optical element [37,38], counter-propagating probe beam direction [39,40] or optical pumping with opposite circular polarisations [41,42].…”

Recent Developments in Fabrication Methods and Measurement Schemes for Optically Pumped Magnetic Gradiometers: A Comprehensive Review

“…It is worth noting that if one cell is used to control the common parameter, such as the modulate frequency or field covering both cells, then the gradiometer will turn into a feedback type and the half-plate will become irrelevant. Using this half-wave-plate intrinsic differential method, Robert J. Cooper et al later designed an intrinsic radio-frequency gradiometer [ 60 ].…”

Two Paths to a Magnetic Gradiometer

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Atomic magnetometers employing two new geometries can exclude background fields to pick up weak, nearby radio-frequency sources.

By Marric StephensF rom the slivers of natural magnetite used as the earliest magnetic compasses to today's cryogenically cooled superconducting quantum interference devices, researchers have employed many diverse means to measure magnetic fields. Now Robert Cooper at George Mason University, Virginia, and colleagues have added two more [1]. Their instruments, which are variations on a high-precision instrument called an optically pumped atomic magnetometer, are the first demonstrations of "intrinsic radio-frequency gradiometers."

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“…At the heart of an optically pumped atomic magnetometer lies a gas of alkali atoms whose spins are aligned by a circularly polarized laser-the optical pump. The presence of an external magnetic field perturbs the spin axis of these atoms, showing up as a change in the polarization direction of the probe beam-a second, linearly polarized laser that is also transmitted Credit: R. J. Cooper et al [1].…”