Buffer-gas pressure dependence of the scale factor in nonlinear magneto-optical rotation magnetometers

Wall-collision relaxation can be effectively suppressed by buffer-gas, leading to a significant enhancement of the scale factor in nonlinear magneto-optical rotation (NMOR) magnetometers. However, as the buffer-gas pressure increases, pressure broadening degrades the efficiency of light-atom interaction; therefore, the buffer-gas effects on relaxation and polarization should be balanced to further improve the scale factor. In this work, a theoretical model is developed to analyze the dependence of the NMOR scale factor on buffer-gas pressure. The scale factor of vapor cells with different buffer-gas pressures is experimentally measured under various experimental conditions. Buffer-gas-induced Ramsey structures, which lead to a pronounced enhancement of the scale factor, are observed in the NMOR magnetic resonance curve. Moreover, increasing pressure is found to strengthen the coupling between partially resolved hyperfine transitions, leading to an additional reduction of the NMOR scale factor in good agreement with the theoretical predictions. This study provides deeper insight into the physical mechanisms of NMOR atomic ensembles and offers practical guidance for optimizing the buffer-gas pressure in NMOR magnetometers.