In situ measurement of triaxial coil constants for optically pumped magnetometer based on higher-order parametric resonance

We demonstrated a method for in-situ measurement of triaxial magnetic field coil constants of optically pumped magnetometer (OPM) operating in the spin-exchanged relaxation-free (SERF) regime based on higher-order parametric resonances. The triaxial coil constants play a vital role in achieving optimal operation of the OPM and amplitude calibration of weak signals such as magnetoencephalography (MEG). The measurement of the triaxial magnetic field coil constants is therefore particularly critical. Compared to the previous methods, our method is convenient and universal for practical application and commercialization. It does not require a complicated fitting process for measurements, and is applicable to both single- and dual-beam configurations of OPMs which are prevalent in current applications. The feasibility of the method is verified by simulation and experiment, and the average measurement errors of the triaxial coil constants of the OPM in single- and dual-beam configurations are 0.75 % and 1.74 %, respectively. This method holds substantial implications for calibrating and optimizing arrayed OPM systems, with the potential to enhance the measurement sensitivity and the accuracy of magnetic source localization in triaxial OPM-MEG systems. •Higher-order parametric resonances for measuring triaxial coil constants of OPMs.•Higher-order parametric resonances of two-mode OPMs were comprehensively analyzed.•Average measurement errors are 0.75% and 1.74% for coil constants of two-mode OPMs.