Zero field optically pumped magnetometer with independent dual-mode operation

We propose a dual-mode optically pumped magnetometer (OPM) that can flexibly switch between single-beam modulation mode and double-beam DC mode. Based on a 4 mm × 4 mm × 4 mm miniaturized vapor cell, the double-beam DC mode achieves a sensitivity of 7 fT/Hz1/2 with probe noise below 4 fT/Hz1/2 and working bandwidth over 65 Hz. This mode is designed to precisely measure the noise floor of a mu-metal magnetic shield. The single-beam modulation mode (sensitivity 20 fT/Hz1/2) exhibits bandwidth characteristics suitable for biomagnetic measurements. Thus, our design is suitable for a miniaturized OPM with multiple functions, including magnetic-shield background noise measurement and medical imaging.