Vector Magnetic Field Detection of Microparticles Using Differential Dual-Pump Magnetometer

A triaxial optically pumped magnetometer (OPM) with high sensitivity is essential for obtaining complete vector magnetic field distributions in magnetic particle detection, and can further facilitate various biological applications centered on magnetic particles. In this study, we present a multichannel triaxial OPM utilizing two nonoverlapping semicircular-shaped pump lights, and the multiple probes are realized by photodiode arrays. This structure doubles the channel number and enables eight independent and simultaneous measurements of the local vector magnetic field. The interchannel responses are investigated for coupling suppression by optimizing the modulation phase. Ultimately, the triaxial sensitivities of 13.3 fT/Hz^1/2 (x-axis), 14.3 fT/Hz^1/2 (y-axis), 14.3 fT/Hz^1/2 (z-axis) are realized, and a differential mode sensitivity of 6.3 fT/Hz^1/2 is further achieved with a 5-mm baseline. Utilizing this OPM system, the vector magnetic fields of a 200-μm magnetic particle are successfully detected for the first time. Taking advantage of the multichannel measurements, the common mode noise is suppressed by a factor of 13 in differential mode. Then the noise-buried magnetic field signal is effectively extracted and agrees well with the simulated wavelet-like waveform. Besides, the differential signals are observed to contain rich information about the particle dynamics, reflecting the triaxial motion of particles. This high-density, low-crosstalk OPM presents an encouraging measurement tool for comprehensive particle characterization and demonstrates promising potential for various medical applications, such as magnetic hyperthermia and drug delivery.