Ultra-sensitive Magnetic Microscopy with an Optically Pumped Magnetometer

Abstract

Optically pumped magnetometers (OPMs) based on lasers and alkali-metal vapor cells are currently the most sensitive non-cryogenic magnetic field sensors. Many applications in neuroscience and other fields require high-resolution, high-sensitivity magnetic microscopic measurements. In order to meet this demand we combined a cm-size spin-exchange relaxation-free (SERF) OPM and flux guides (FGs) to realize an ultra-sensitive FG-OPM magnetic microscope. The FGs serve to transmit the target magnetic flux to the OPM thus improving both the resolution and sensitivity to small magnetic objects. We investigated the performance of the FG-OPM device using experimental and numerical methods, and demonstrated that an optimized device can achieve a unique combination of high resolution (80 μm) and high sensitivity (8.1 pT/). In addition, we also performed numerical calculations of the magnetic field distribution in the FGs to estimate the magnetic noise originating from the domain fluctuations in the material of the FGs. We anticipate many applications of the FG-OPM device such as the detection of micro-biological magnetic fields; the detection of magnetic nano-particles; and non-destructive testing. From our theoretical estimate, an FG-OPM could detect the magnetic field of a single neuron, which would be an important milestone in neuroscience.

Nondestructive in-line sub-picomolar detection of magnetic nanoparticles in flowing complex fluids

“…It is important to emphasize here that the sensitivity of the presented measurement may significantly improve further by the use of magnetic flux- guides/concentrators 45 , where, for example, the detection of single micron-size particles has been recently demonstrated using a similar detection system 46 .…”

A High-Sensitivity Tunable Two-Beam Fiber-Coupled High-Density Magnetometer with Laser Heating

“…Still, our demonstrated sensitivity is comparable to that of other state-of-the-art AMs and SQUIDs. In some cases, our low-temperature magnetometer will have advantages when the object needs to be placed within a minimal distance from the sensor area (e.g., micro-fluidic remote NMR detection [33] and flux-concentrator enhancements in sensitivity [34,35]).…”

Miniaturized Magnetic Sensors for Implantable Magnetomyography

“…However, compared with the magnitude of EMG signals in the scale of milli‐volts, the MMG signal is extremely small and just in the range of pico (10 −12 ) to femto (10 −15 ) Tesla, [ 12 ] decreasing with the distance between the measurement point and the skeletal muscle. Figure illustrates the progress pathway of the biomagnetic sensors from SQUIDs, [ 1 ] atom magnetometer, [ 13,14 ] OPMs, [ 10,15 ] thin‐film solid‐state magnetic sensors, [ 16 ] to spintronic devices. [ 17,18 ] In a seminal work of Cohen and Gilver in 1972, they discovered and recorded MMG signals using superconducting quantum interference devices (SQUIDs).…”