铯原子喷泉钟空间均匀C场的研究

Study on C field's spatial uniformity for cesium fountain clock

二阶塞曼频移是影响铯原子喷泉钟频率不确定度性能的系统项之一,而二阶塞曼频移的不确定度由C场均匀度决定。C场均匀度又与C场强度随时间的变化情况(时间稳定性)和C场强度沿原子飞行路径的变化情况(空间均匀性)有关。均匀C场的实现有两种途径:一是磁屏蔽的屏蔽效果好且无剩磁;二是在磁屏蔽两端加补偿线圈,但是补偿线圈会引入电噪声而降低C场的时间稳定性。首先理论研究了由C场引起的二阶塞曼频移,和由C场空间均匀度引起的二阶塞曼频移不确定度。实验上通过改进退磁方法对磁屏蔽进行了整体退磁,得到了无补偿情况下空间均匀度良好的剩磁47cm@1nT,和C场48cm@1.5nT。最后计算得到二阶塞曼频移为68.7×10^(-15),由C场空间均匀度引起的二阶塞曼频移不确定度为6.05×10^(-19)。

The uniformity of C field determines the second-order Zeeman frequency shift, which is the major physical factor that influences the frequency uncertainty of the cesium atomic fountain clock. And C field＇s uniformity relates to time stability and spatial uniformity along the atom trajectory. There＇re two ways to implement a uniform C field.the magnetic shielding has no residual magnetism with high quality; add compensation coils to both ends of the magnetic shielding, but it may introduce electrical noise and reduce time stability. In this paper,we theoretically studied second-order Zeeman frequency shift caused by C field and second-order Zeeman frequency shift＇s uncertainty caused by C field special uniformity firstly. In experiment, by demagnetizing the magnetic shielding integrally, we obtained a fairly uniform residual magnetism which fluctuates less than 1 nT in 47 cm, and C field fluctuates less than 1. 5 nT in 48 cm without compensation. Finally,we calculated and analyzed the results, the second-order Zeeman frequency shift is 68.7×10^-15 ,and the second-order Zeeman frequency shift＇s uncertainty caused by C field spatial uniformity is 6.05 ×10-19.