A method for calibrating coil constants by using an atomic spin co-magnetometer

Abstract: Spin polarized noble gases can precess in an applied magnetic field by referring toLarmor precession, based on which we present a novel method to calibrate magnetic coilconstants with hyperpolarized helium-3 by using an atomic spin magnetometer based onpotassium. Spin polarized alkali metal atoms can hyperpolarize the helium-3 gas viaspin-exchange optical pumping. After several hours of polarization, the polarization ofhelium-3 goes into a steady state, then optical pumping is stopped to realize a darkstate. In such a dark state, the Larmor precession of hyperpolarized helium-3 in anapplied magnetic field can be detected by spin-polarized alkali metal atoms, which are notinfluenced by the additional magnetic field induced by light shift. Through analyzing andextracting this Larmor precession frequency, the magnitude of the applied magnetic fieldcan be obtained. Experimental results show that the residual magnetic field in themagnetic shielding is 5.50 ±0.05 nT, and the coil constants are 163.02 ± 0.18 nT/mA, 168.22 ± 0.06 nT/mA, and 137.05 ± 0.04 nT/mA in the x, y and z directions,respectively. Graphical abstract: [Figure not available: see fulltext.]