The transmission characteristics of electromagnetic (EM) waves in a semicircular plasma filament layer generated by a femtosecond laser were studied in a wide frequency band including radar waves. We have focussed on the influence of plasma parameters and filament arrangement based on the diffraction and superposition theory of EM waves on the transmittance. A numerical simulation model using the current density convolution finite-difference time-domain method was constructed in a semicircular multilayer filament structure, and the transmission characteristics of spherical EM waves were examined. The simulation results showed that in this semicircular structure, the transmittance was periodically changed at a frequency interval corresponding to the thickness of the filament channel. This phenomenon was more pronounced as the number of the filament layers increased. In the lower band (<30 GHz), there was little change in the transmittance according to layer-to-layer distance, but in the higher band (>30 GHz), it changed irregularly. On the contrary, for the electron number density, it changed regularly in the lower frequency and hardly changed in the higher frequency. When the number of layers was 3 or more, the transmittance became 0 at the centre of the channel, and a discontinuous interference pattern appeared more clearly as the frequency increased.

中文翻译：

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飞秒激光产生的半圆形等离子体细丝层中电磁波的传输特性

在包括雷达波在内的宽频带内研究了由飞秒激光器产生的半圆形等离子体细丝层中电磁 (EM) 波的传输特性。我们基于电磁波的衍射和叠加理论，重点研究了等离子体参数和灯丝排列对透射率的影响。在半圆形多层灯丝结构中构建了使用电流密度卷积有限差分时域方法的数值模拟模型，并研究了球形电磁波的传输特性。仿真结果表明，在这种半圆形结构中，透射率以与灯丝通道厚度相对应的频率间隔周期性变化。随着细丝层数的增加，这种现象更加明显。在较低频段（<30 GHz），透射率随层间距离变化不大，但在较高频段（> 30 GHz），它的变化不规则。相反，电子数密度在低频有规律地变化，高频几乎没有变化。当层数为3或更多时，通道中心的透射率变为0，并且随着频率的增加，不连续的干涉图案出现得更清楚。它在较低频率有规律地变化，在较高频率几乎没有变化。当层数为3或更多时，通道中心的透射率变为0，并且随着频率的增加，不连续的干涉图案出现得更清楚。它在较低频率有规律地变化，在较高频率几乎没有变化。当层数为3或更多时，通道中心的透射率变为0，并且随着频率的增加，不连续的干涉图案出现得更清楚。