The electromagnetic pulse (EMP) emitted from the plasma produced by interaction of 5-ns pulsed Nd:YAG ( $\lambda =532$ nm) laser with the aluminum target was measured. The laser irradiance at the target was varied in the range of $3.12\times 10^{9} - 4.56\times 10^{10}$ W/cm² and its influence on the temporal and spectral parameters of the EMP was investigated. The EMP starts well after the termination of laser pulse and the duration of EMP is up to several hundred nanoseconds. The EMP start time was found to decrease from approximately 150 to 60 ns with the rise of laser irradiance. The rise time of EMP (~50 ns) does not seem to vary with the laser irradiance. The signal consists of several resonance peaks in the frequency bin of 20–200 MHz, whose intensity also depends on the laser irradiance. The observed dependence of EMP intensity on the laser irradiance and frequency of fundamental-mode emission is compared with the theoretical predictions. The considerable delayed emission of EMP indicates that its origin can be related to the macroscopic charge separation phenomena during the plasma expansion.

中文翻译：

---

纳秒脉冲激光铝等离子体发射电磁脉冲的时间和光谱表征

由 5 ns 脉冲 Nd:YAG 相互作用产生的等离子体发射的电磁脉冲 (EMP) $\lambda =532$ nm) 激光与铝靶进行了测量。目标处的激光辐照度在以下范围内变化 $3.12\times 10^{9} - 4.56\times 10^{10}$ 宽/厘米²并研究了它对 EMP 的时间和光谱参数的影响。EMP 在激光脉冲终止后很好地开始，EMP 的持续时间可达数百纳秒。随着激光辐照度的增加，发现 EMP 开始时间从大约 150 ns 减少到 60 ns。EMP 的上升时间 (~50 ns) 似乎不随激光辐照度而变化。该信号由 20-200 MHz 频率区间中的几个共振峰组成，其强度也取决于激光辐照度。观察到的 EMP 强度对激光辐照度和基模发射频率的依赖性与理论预测进行了比较。EMP 相当大的延迟发射表明其起源可能与等离子体膨胀过程中的宏观电荷分离现象有关。