Spin-decoupling calibration method for coil constants in optically pumped comagnetometers

The magnetic coil constant is a critical parameter in optically pumped comagnetometers (OPCMs), as it directly determines the accuracy of applied magnetic fields and affects both system characterization and feedback control performance. This paper presents a spin-decoupling calibration (SDC) method, which introduces a longitudinal decoupling field along the pumping axis to drive the atomic ensemble into a spin-decoupling regime. In this regime, triaxial coil constants are determined in situ via the nuclear spin Larmor precession frequency. Comprehensive experiments conducted under five distinct optical pumping power densities validate the method's strong robustness and high precision. Compared to the dark-state calibration approach, the SDC method reduces the relative standard error (RSE) by 62.1%, 55.1%, and 58.5% along the z-, y-, and x-axes, respectively, and lowers the mean calibration uncertainty (MU) by 43.3%, 12.1%, and 17.4%. These results demonstrate that the SDC method achieves robust and precise coil constant calibration under varying operating conditions, offering significant advantages for long-term deployment and closed-loop control in OPCMs.