为了研究高能脉冲CO2激光诱导空气等离子体放电通道的特性, 建立了高压电容充放电实验平台, 激光束经离轴抛物聚焦镜汇聚, 引发间距可调的盘状电极和针状电极之间的等离子体放电通道。利用电气参量测量、发射光谱测量等手段, 分析了等离子体放电通道的启动特性、阻抗特性和等离子体密度。结果表明, 激光束与放电方向同轴的结构以及较大的脉冲能量, 使得激光诱导等离子体放电通道的启动时间大幅缩短, 50mm间距的等离子体通道, 启动时间约为2μs; 激光诱导等离子体放电通道的阻抗很小, 约1Ω~2Ω, 并且阻抗值随放电电压的增加有减小的趋势, 而与等离子体通道长度的关系不明显; 由谱线的Stark展宽计算获得的空气击穿之后、放电启动之前的等离子体电子密度约为1019cm-3, 尽管放电启动时等离子体辐射显著增强, 但等离子体密度近乎单调下降。这些结果将有利于高能脉冲CO2激光诱导空气等离子体放电通道的应用研究。

In order to study characteristics of discharge channels of air plasma induced by high-energy pulsed CO2 laser, a charging and discharging experimental setup of high voltage capacitor was established, in which the pulsed laser beam was focused by a parabolic reflector to trigger the plasma channel in the adjustable gap between a disk-like electrode and a needle-like electrode. Based on the measurements of electric parameters and emission spectra, the characteristics on start-up, impedance and plasma density of the discharge channel were analyzed. It is found that the start-up time become much shorter benefited from the high pulsed-energy and coaxial structure of laser beam and discharge direction, for a plasma channel with length of 50mm, the start-up time of the discharge was only about 2μs; the discharge channel has rather low impedance of 1Ω~2Ω, and this impedance has a decreasing tendency with the increasing of discharge voltage, which has no significant correlation with the length of plasma channel; the electron density after the laser-induced breakdown and before the electric discharge is on the level of 1019 cm-3 calculated from the Stark broadening of the emission lines, though the emission become much stronger after the startup of electric discharge, the plasma density keeps decreasing. These results will be helpful for the application of laser-induced plasma channel.