Abstract
We have developed a four-channel optically pumped atomic magnetometer for magnetoencephalography (MEG) that incorporates a passive diffractive optical element (DOE). The DOE allows us to achieve a long, 18-mm gradiometer baseline in a compact footprint on the head. Using gradiometry, the sensitivities of the channels are < 5 fT/Hz1/2, and the 3-dB bandwidths are approximately 90 Hz, which are both sufficient to perform MEG. Additionally, the channels are highly uniform, which offers the possibility of employing standard MEG post-processing techniques. This module will serve as a building block of an array for magnetic source localization.
Highlights
The dominant technology for human biomagnetic measurements has been liquid-heliumcooled superconducting quantum interference device (SQUID) magnetometers because their high sensitivity makes them capable of detecting the very weak signals from humans [1]
Using the operating conditions of our optically pumped (atomic) magnetometers (OPMs) in the model, we find that when the transverse magnetic field is zero, the strong optical pumping power allows the pump laser to highly spin polarize the atoms and bleach the vapor through the cell, even though the optical depth is very high for the unpolarized vapor [Fig. 4(b)] [41]
Conclusions and future work We have developed a new, four-channel OPM sensor whose design incorporates a diffractive optical element (DOE) for the detection of biomagnetic fields, those in MEG
Summary
The dominant technology for human biomagnetic measurements has been liquid-heliumcooled superconducting quantum interference device (SQUID) magnetometers because their high sensitivity makes them capable of detecting the very weak signals from humans [1]. Common biomagnetic applications include measurement of the magnetic fields from the heart, magnetocardiography (MCG) [2], and from the brain, magnetoencephalography (MEG) [3]. For these applications, though, optically pumped (atomic) magnetometers (OPMs) have emerged as a promising replacement for SQUIDs [4, 5]. The sensitivity and bandwidth of OPMs are sufficiently high to observe MCG and MEG signals of interest, but OPMs operate at or above room temperature, so no liquid helium infrastructure is required. Without a liquid helium dewar, the size of an OPM instrument may be much smaller than SQUID systems, and the OPMs may be reconfigurable. Existing tools for analysis and interpretation of SQUID systems may be adapted to an OPM system [6]
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