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Polarized laser-induced fluorescence spectroscopy for measuring electric field distribution in plasmas

用于测量等离子体电场分布的偏振激光诱导荧光光谱

基本信息

批准号：
08680506
负责人：
TAKIYAMA Ken
金额：
$ 1.54万
依托单位：
HIROSHIMA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1997
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-08680506/
关键词：
Laser-induced fluorescence Polarization spectroscopy Plasma diagnostics Electric field distribution

项目摘要

We have developed a spectroscopic method to measure sheath electric field distribution of discharge plasma. The electric field can be determined by the polarization degree of allowed fluorescence induced by pulsed laser excitation of metastable He atoms through forbidden transition, i.e.Stark and electric quadrupole moment transitions. To apply our method to a plasma with higher electron and/or gas density, it is indispensable to measure accurately the degree of polarization at the rising part of laser-induced fluorescence (LIF) pulse. We developed a fast LIF detection system (the rise time of 1 ns) which simultaneously recorded two polarization components (p and s) of LIF pulse separated by Glan-Thompson polarizing beam splitter. Using the system, LIF signals were observed in the sheath region of a He glow discharge plasma. The polarization decayd remarkably because the excited atoms frequently collided with ground state atoms in the plasma. A rate-equation model including the collisional depolarization process, which is also developed in the present study, was employed to analyze these data and then the electric field distribution was successfully obtained. It was demonstrated that our method can be applied to the system with fast depolarization rate of 10^8s^<-1>. From the obtained LIF intensity the possible spatial resolution was estimated to be about 0.1mm if the density of metastable atoms was -10^<10>cm^<-3>. It was also shown that the method was applicable to the case that magnetic field was applied.

本文发展了一种测量放电等离子体鞘层电场分布的光谱方法。该电场可以由脉冲激光激发亚稳He原子通过禁戒跃迁（Stark跃迁和电四极矩跃迁）诱导的允许荧光的偏振度来确定。为了将该方法应用于具有较高电子和/或气体密度的等离子体，必须精确测量激光诱导荧光（LIF）脉冲上升段的偏振度。我们研制了一种快速LIF探测系统（上升时间为1 ns），该系统可同时记录由Glan-Thompson偏振分束器分离的LIF脉冲的两个偏振分量（p和s）。利用该系统，在He辉光放电等离子体鞘层区域观察到LIF信号。由于等离子体中激发态原子与基态原子频繁碰撞，极化强度显著衰减。采用本研究中发展的包含碰撞退极化过程的速率方程模型对这些数据进行了分析，成功地得到了电场分布。结果表明，该方法可以应用于快速退偏速率为10^8s^的系统<-1>。从所获得的LIF强度估计，如果亚稳原子的密度为约10 μ cm-3，则可能的空间分辨率为约0.1mm<10><-3>。计算结果还表明，该方法适用于外加磁场的情况。