Optimizing Nitrogen Concentration and Temperature for Reducing Spin Relaxation in Spin‐Exchange Relaxation‐Free Co‐Magnetometers

Abstract This study systematically investigates the spin relaxation characteristics of alkali‐metal atoms in spin‐exchange relaxation‐free (SERF) co‐magnetometers, focusing on mitigating the radiation trapping to reduce the alkali‐metal spin relaxation rate. Radiation trapping is one of the dominant mechanisms exacerbating spin relaxation in alkali‐metal atoms and is conventionally suppressed by introducing nitrogen () as a quenching agent. However, experiments reveal that the typical concentration in current SERF co‐magnetometers is insufficient to effectively suppress radiation trapping. By increasing the quenching gas concentration, additional attenuation of the radiation trapping effect is achieved. Meanwhile, to address the enhanced spin‐exchange collision relaxation arising from higher concentration, the operating temperature is adjusted to increase the alkali‐metal atom number density, thereby effectively curtailing this adverse effect. Experimental results demonstrate that the synergistic optimization of concentration and temperature reduces alkali‐metal spin relaxation by approximately 55% and decreases the noise power spectral density of the co‐magnetometer by 48.5% at 1 Hz. These findings confirm the effectiveness of this approach in improving the accuracy and sensitivity of SERF co‐magnetometers.