High-sensitive laser spectroscopic method using atomic interference to measure microscopic electric field in plasmas

我们提出了一种利用氦原子的激光诱导荧光(LIF)直接测量等离子体中电场的灵敏方法。在这种激光诱导荧光技术中，由于斯塔克诱导的电偶极子和电四极跃迁，亚稳态氦原子(2^1S→4^1D)被禁止激发后，只观察到允许的荧光(4^1D→2^1P)的线性极化，就可以测量电场。在磁化等离子体的情况下，一种新的高灵敏度激光诱导荧光方法将成为可能。磁场与电场的交叉作用会引起斯塔克振幅和QDP振幅之间的干涉。禁忌激发产生了量子数(取向)符号相反的磁子能级间的各向异性布居，例如m_L=1和-1。在LiF的圆极化分量中，各向异性表现为二向色性。由干涉引起的圆极化程度与电场的关系是理论上的…更多地基于LIF过程中涉及的转变的选择规则来计算LLY。结果表明，圆二向色性比线性二向色性具有更高的灵敏度(最小检测电场为10V/cm)和较宽的动态范围。采用圆柱形空心阴极放电，在阴极暗空间中施加垂直于电场的磁场，进行了模型式实验。我们同时观察到沿磁场方向等离子体中LIF的两个圆偏振分量。观察到的LIF在鞘内呈强极化。偏振度与理论计算值相吻合。值得注意的是，在等离子体中首次观察到了干扰效应。根据上述事实，我们可以得出这样的结论：圆二向色性的使用将使测量等离子体的微观电场与宏观电场分开成为可能。较少

We have proposed a sensitive method to directly measure the electric field in plasmas by using a laser-induced fluorescence (LIF) of a helium atom. In this LIF technique the electric field can be measured by observing only the linear polarization of the allowed fluorescence (4^1D→2^1P) subsequent to the forbidden excitation of metastable He atoms (2^1S→4^1D) due to the Stark-induced electric dipole and the electric quadrupole (QDP) transitions. In the case of the magnetized plasma a new high sensitive LIF method will be possible. The crossed magnetic field to electric field can induce the interference between the Stark and QDP amplitudes. The forbidden excitation generates anisotropic population between magnetic sublevels with opposite sign of quantum number (orientation), e.g. m_l = +1 and -1. The anisotropy appears as the dichroism in circular polarization components of LIF.The electric field dependence of the degree of circular polarization induced by the interference was theoretica … More lly calculated based on the selection rules of the transitions involved in the LIF process. It showed that the circular dichroism has high sensitivity (the minimum detectable electric field : 10 V/cm) and wide dynamic range as compared with the linear one. A model-type experiment was performed with a cylindrical hollow cathode discharge with the magnetic field applied perpendiculany to the electric field in the cathode dark space. We observed simultaneously both the circularly polarized components of LIF from the plasma along the magnetic field direction. The observed LIF was strongly polarized in the sheath. The degree of the polarization agreed with a theoretically calculated value. It should be noted that in the plasma the interference effect was observed for the first time. From the facts described above we may conclude that the use of the circular that the use of the circular dichroism will make it possible to measure the microscopic electric field of the plasma separately to the macroscopic one. Less