Abstract
A multichannel imaging system is presented, consisting of 25 microfabricated optically-pumped magnetometers. The sensor probes have a footprint of less than 1 cm2 and a sensitive volume of 1.5 mm × 1.5 mm × 1.5 mm and connect to a control unit through optical fibers of length 5 m. Operating at very low ambient magnetic fields, the sensor array has an average magnetic sensitivity of 24 fT/Hz1/2, with a standard deviation of 5 fT/Hz1/2 when the noise of each sensor is averaged between 10 and 50 Hz. Operating in Earth's magnetic field, the magnetometers have a field sensitivity around 5 pT/Hz1/2. The vacuum-packaged sensor heads are optically heated and consume on average 76 ± 7 mW of power each. The heating power is provided by an array of eight diode lasers. Magnetic field imaging of small probe coils was obtained with the sensor array and fits to the expected field pattern agree well with the measured data.
Highlights
Magnetic imaging is a powerful tool that can be applied at many different spatial and temporal scales
Magnetic field imaging of small probe coils was obtained with the sensor array and fits to the expected field pattern agree well with the measured data
Acknowledgments We thank Susan Schima for her help with fabrication and assembly
Summary
Magnetic imaging is a powerful tool that can be applied at many different spatial and temporal scales. This results in a sensitivity of approximately 1 fT/√Hz for a volume of 1 mm, scaling as 1/√V Other performance parameters such as bandwidth, linearity, slew rate, and dynamic range, as well as operational parameters like size, power consumption, and possible array spacing play a role in the choice of sensor for a particular application. If a much larger array spacing than the fiber-coupled system is desired, our technology could be implemented using a free-space laser beam to link the sensor head with the control unit [11]. This approach could allow for inexpensive, microfabricated, and completely passive sensor heads that can remain dormant without consuming any power until optically heated and interrogated by light.
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