Three-axis magnetic field detection with a compact, high-bandwidth, single beam zero-field atomic magnetometer

Zero-field optically pumped magnetometers (OPMs) have emerged as an important technology in the realm of biomagnetic research, providing extremely small magnetic field detection capabilities, femtotesla-level, contained in a non-cryogenic compact form factor. Often, compact zero-field OPMs extract single or two-axis magnetic information, typically with a sensing bandwidth of < 100 Hz. The resolution of multiple axes of magnetic field is particularly important for accurate representation of radial components of biomagnetic fields. However, the presence of multi-axis static magnetic fields across the OPM causes measurement errors that degrade signal resolution. Here, we utilise our compact caesium single beam zero-field OPM to address these limitations. We magnetically modulated along both transverse axes of the sensor, at unique frequencies, to extract all axes static-field information. Active feedback can be realised through a lock-in detection scheme at f_Mod,x/y for the x- and y-axes, and at 2f_Mod,x for the beam axis, z. Operation in this scheme allows for the extraction of three-axis magnetic field information from only a single beam and highlights the importance of active feedback in high-sensitivity biomagnetic applications. The portable sensor also demonstrates a bandwidth with a -3 dB point at ≃ 1600 Hz. The combination of high bandwidth and the capability to extract three-axis magnetic fields opens up exciting prospects for resolving high-frequency biomagnetic signals.