Basic Study for the Control of Lightning Using Laser-Induced Discharge and the Useful Method of Lightning Energy

本课题研究了长、短间隙下激光诱导放电的基本过程。主要研究内容如下：利用马赫-曾德尔干涉仪测量了CO_2激光在空气中诱导等离子体的扩散速度。根据我们的测量，等离子体作为冲击波以18公里/秒的速度膨胀。等离子体以18 km/s的速度膨胀为激波。我们估计激光产生的等离子体起导体的作用，因为随着激光能量的加热，它膨胀并使周围的气体变薄。等离子体对激光能量的吸收率取决于激光的种类。CO_2激光、YAG激光和K_2F_3准分子激光的吸收率分别为输入能量的99.7%、70 - 80%和20 - 30%。50%的人认为<50>在一定条件下，激光诱导等离子体使过电压（V_）降低约四分之一。在几乎所有的实验中，我们都观察到等离子体的产生和完全击穿之间有一个很长的时滞。这种时滞的变化与所施加的电压和压力有关，而与所用激光的种类或激光能量无关。在我们的实验范围内，当<50>时滞在几十μ s到100 μ s之间时，V_<50>（？）当与正常的50%火花过电压相比时，该特性相反。

In this project we studied the basic process of laser-induced discharge under short and long gaps. Summary of research is as follows:We measured the diffusing speed of the plasma induced in the air by CO_2 laser using Mach-Zender interferometer. According to our measurements, the plasma expands at the speed of 18 km/sec as a shock wave. expands at the speed of 18 km/sec as a shock wave.We estimate that the plasma produced by laser acts as a conductor, because as the laser energy heats up, it expands and thins down the surrounding gas.The absorption rate of laser energy by plasma is different depending upon the kind of laser. The absorption rate is 99.7%, 70 - 80% and 20 - 30% of the input energy in the case of the CO_2 laser, the YAG laser and the KgammaF excimer lasers respectively.50% speak over voltages(V_<50>) decrease about one fourth by means of the plasma induced by laser in some conditions, but they gardly change in other conditions.We observed in almost all experiments a long time-lag between plasma production and complete breakdown. This variation of time-lag depends on applied voltage and pressure rather than the kind of laser used or the laser energy.In the range of our experiments, V_<50> are decreased to a minimum when the time-lag mentioned above is between several 10 mus and 100 mus.When the electrode combination is plate vs. rod in the case of laser-induced discharge, we found that V_<50> are higher if plate electrode is negative than if it is positive. This characteristic is reversed when compared to normal 50% spark over voltages.