We describe a multichannel magnetoencephalography (MEG) system that uses optically pumped magnetometers (OPMs) to sense the magnetic fields of the human brain. The system consists of an array of 20 OPM channels conforming to the human subject’s head, a person-sized magnetic shield containing the array and the human subject, a laser system to drive the OPM array, and various control and data acquisitions systems. We conducted two MEG experiments: auditory evoked magnetic field (AEF) and somatosensory evoked magnetic field (SEF), on three healthy male subjects, using both our OPM array and a 306-channel Elekta-Neuromag superconducting quantum interference device (SQUID) MEG system. The described OPM array measures the tangential components of the magnetic field as opposed to the radial component measured by most SQUID-based MEG systems. Herein, we compare the results of the OPM- and SQUID-based MEG systems on the auditory and somatosensory data recorded in the same individuals on both systems.

A non-invasive functional-brain-imaging system based on optically-pumped-magnetometers (OPM) is presented. The OPM-based magnetoencephalography (MEG) system features 20 OPM channels conforming to the subject's scalp. Due to proximity (12 mm) of the OPM channels to the brain, it is anticipated that this MEG system offers an enhanced spatial resolution as it can capture finer spatial features compared to traditional MEG systems employing superconducting quantum interference device (SQUID). We have conducted two MEG experiments on three subjects: somatosensory evoked magnetic field (SEF) and auditory evoked magnetic field (AEF) using our OPM-based MEG system and a commercial SQUID-based MEG system. We have cross validated the robustness of our system by calculating the distance between the location of the equivalent current dipole (ECD) yielded by our OPM-based MEG system and the ECD location calculated by the commercial SQUID-based MEG system. We achieved sub-centimeter accuracy for both SEF and AEF responses in all three subjects.

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/Hz 1/2 , 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. References and links 1. K. Sternickel and A. I. Braginski, "Biomagnetism using SQUIDs: status and perspectives," Supercond. Sci.Technol. 19(3), S160-S171 (2006). 2. H. Koch, "Recent advances in magnetocardiography," J. Electrocardiol. 37(Suppl), 117-122 (2004) Phys. Rev. A 5(2), 968-984 (1972). 38. M. Rosatzin, D. Suter, and J. Mlynek, "Light-shift-induced spin echoes in a J=1/2 atomic ground state," Phys.

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We demonstrate a two-dimensional (2D) polarization-independent resonant subwavelength grating (RSG) in a filter array. RSGs, also called guided mode resonant filters, are traditionally one-dimensional gratings; however, this leads to TE and TM resonances at different wavelengths and with different spectral shape. A 2D grating can remove the polarization dependence at normal incidence, while maintaining the desirable RSG properties of high reflectivity, narrow passband, and low sidebands without ripple. We designed and fabricated 2D gratings with near-identical responses for both polarizations at normal incidence in the telecommunication band. Ninety percent reflectivity is achieved at the resonant wavelengths.