Optimal buffer gas pressure in dual-beam spin-exchange relaxation-free magnetometers

Optically pumped magnetometers (OPMs) operated in the spin-exchange relaxation-free (SERF) regime have emerged as prevailing biomagnetism measurement devices. The buffer gas in vapor cells can suppress wall collision relaxation but introduce unexpecting destruction relaxation, so as to be crucial to determine the magnetometer performance. In this study, we demonstrated the optimal buffer gas pressure of a dual-beam high sensitivity SERF magnetometer theoretically and experimentally. An optimization model was proposed revealing that the maximum response signal was dependent on the combined effects of the spin-relaxation rate and the pressure broadened linewidth of optical absorption. Six 3 mm × 3 mm × 3 mm Rb-N₂ vapor cells with different gas pressures were fabricated and constructed in a dual-beam SERF magnetometer to verify the optimal gas pressure model. The experimental results coincided well with the theoretical analysis, and a sensitivity of 4 fT/Hz^1/2 was achieved.