Dual-resonance single-beam triaxial spin-exchange relaxation-free magnetometer.

Triaxial measurement of the magnetic field has been proven to be advantageous in magnetoencephalography applications. To achieve triaxial measurement, we develop a single-beam three-axis spin-exchange relaxation-free (SERF) magnetometer in this study. Here, the ability of three-axis measurement is based on a dual-resonance effect discovered, to the best of our knowledge, for the first time in the SERF regime. By applying a rotating field with a frequency of a few hundred Hz, two resonances, i.e., parametric resonance and Mz resonance, are excited simultaneously. The parametric resonance enables field measurement in x and y directions, while the Mz resonance enables field measurement in the z direction. Magnetic field sensitivities of about 40 fT/Hz^1/2 in x- and y-axes and about 50 fT/Hz^1/2 in the z-axis are achieved.