Abstract:To improve the detection sensitivity of spinexchangerelaxationfree (SERF) atomic magnetometer, a method is proposed by increasing the optical range of the detection light, which interacts with the pump light in the gas chamber. This method usesthe technique of establishing Herriott multipass cell outside theatomic gas chamber.And thewhole system is placedinsidetheshieldingcylinder.Themagneticfreedetectionsystemis designedandmanufactured by 3Dsoftware.Comparedwith thetraditionalSERF atomicmagnetometer, itachieves the sensitivity that is not lower than 34 fT/Hz1/2 at multiple frequency points. The problem of combining the complex optical structure with atomic magnetometer can be solved. It provides a good foundation for further improving the performance of the magnetometer by using FP integral cavity in the future.