Portable single-beam atomic total-field magnetometer for stand-off magnetic sensing

Optically pumped atomic magnetometers (OPAMs) offer high sensitivity at room temperature and are increasingly considered for portable magnetic sensing in geomagnetic-field environments. Here, we report a handheld-scale, single-beam scalar 87Rb OPAM with a sensor-head volume of approximately 110 ml. The device operates in an all-optical Bell–Bloom configuration and uses digital lock-in, dispersive tracking of the 87Rb Larmor resonance, implemented with a hybrid electronics stack that combines in-house control hardware with commercial modules. A single frequency-modulated laser beam performs both pumping and probing without RF coils. All signal processing is realized in Python on a single-board computer paired with a commercial off-the-shelf data-acquisition module, enabling immediate deployment without dedicated signal-processing hardware. The magnetometer has an intrinsic in-band field sensitivity of approximately 21 pT/Hz, estimated from the lock-in dispersion slope, over a 0.1–30 Hz closed-loop in-band region with a digital-output rate of 200 samples/s. In an unshielded Earth-field deployment, we detect repeatable transient magnetic signatures from a controlled elevator motion sequence and quantify standoff observability over sensor-elevator distances from 1.25 m to 10 m. These results show that compact scalar OPAMs can provide bandwidth and range-resolved event sensitivity suitable for field-deployable magnetic anomaly detection and infrastructure monitoring in realistic geomagnetic environments.