Development of high-sensitivity portable optically pumped atomic magnetometer with orthogonal pump and probe laser beams

Optically pumped atomic magnetometers (OPAMs) have been demonstrated to show sensitivities better than the order of a few femtoteslas. In this study, we developed a portable potassium OPAM module using an electrically heated oven and orthogonal pump and probe beams coupled from polarization-maintaining optical fibers. The OPAM module shared a volume as small as 700 cm³, and its footprint was as small as 60 × 60 mm²; it operated with a single-channel sensitivity of 14 fT_rms/Hz^1/2 at 100 Hz when the 2-cm cubic potassium cell was heated to 180 °C. In our module, the optical beam path was folded along the magnetic field to be measured. The development of a magnetic sensor device comprising an array of OPAM modules will be an important step toward realizing a biomagnetic imaging system based on OPAMs. The orthogonal two-beam OPAMs will be beneficial for realizing a flexible placement of the array.