Magnetocardiography with a 16-channel fiber-coupled single-cell Rb optically pumped magnetometer

We have constructed a low-cost, portable, high-sensitivity 16-channel optically pumped magnetometer (OPM), operating in the spin-exchange relaxation-free regime, and demonstrated its applications in magnetocardiography (MCG). The decrease in the cost of sensors by an order of magnitude is achieved by the 16-channel operation realized in a single module using a single large flat pancake rubidium vapor cell, broad pump and probe laser beams, and a 16-channel photodiode array. The OPM is also based on a fiber-coupled nearly parallel-beam configuration to facilitate multichannel design and make the system portable. For human MCG experiments, the 16-channel OPM which includes optical components is placed inside a wooden enclosure for laser safety. The enclosure is set on a nonmagnetic table inside a magnetically shielded room, while the lasers and electronics are placed outside the shielding room, to avoid magnetic noise. We show that the 16-channel OPM enables simultaneous imaging of human cardiac activity on...