Absorption of 10 GHz electromagnetic waves by femtosecond filaments array
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摘要: 为了研究飞秒光丝阵列对10 GHz电磁波的吸收特性，建立了飞秒光丝阵列吸收电磁波的有限元模型，研究了光丝内电子温度、电子数密度、光丝直径和电磁波的极化等参数对吸收系数的影响。研究结果表明：当电磁波偏振方向与光丝轴向垂直时，阵列对电磁波是透明的；增加光丝内电子数密度或提高电子温度，吸收系数先增大后减小；当光丝直径与电磁波趋肤深度相等时，吸收系数达到最大值。对于S极化电磁波，当光丝直径为50 μm时，吸收系数随入射角的增大而变大；当光丝直径为100~200 μm时，在入射角较小时，吸收系数随入射角的增大而变大；在入射角较大时会出现吸收峰值，最高可达0.45，且光丝直径越大，吸收峰值对应的入射角就越小；对于P极化电磁波，吸收系数随入射角增大而降低。Abstract: In order to study the absorption characteristics of 10 GHz electromagnetic (EM) waves by femtosecond filaments array, the interaction model of electromagnetic wave and femtosecond filaments array is established, and the absorption coefficients with electron temperature, electron density, filament diameter, and EM polarization are calculated by the finite element method (FEM). The results indicate that the plasma filaments array becomes transparent for EM wave when the polarization of the EM waves is perpendicular to the filaments axis. The absorption coefficient increases first and then decreases with the increasing of the filaments electron density or electron temperature, when skin depth of EM wave is equal to the diameter of the filament, the absorption coefficient reaches the maximum. For the S-polarized EM wave, the absorption coefficient increases with incident angle when the diameter of the filament is 50 μm. There is an absorption peak at large angle when the filament diameter is between 100 μm to 200 μm, and the incident angle responding to the peak absorption is decreasing with the diameter of the filaments. For the P-polarized EM wave, the absorption coefficient is decreasing with the incidence angle of the EM wave.
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Key words:
- femtosecond filaments /
- array /
- electromagnetic wave /
- absorption coefficient /
- skin depth
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图 1 飞秒光丝阵列与电磁波相互作用的几何示意图
Figure 1. Geometry used to describe the interaction of the incident microwave with the array made of cylindrical plasma filaments
图 2 数值计算中电磁波的极化情况
Figure 2. Polarization of incident electromagnetic wave in numerical calculation
图 3 电子数密度和电子温度对10 GHz电磁波的反射、透射和吸收系数的影响
Figure 3. Influence of the temperature and density of electrons on the transmission, reflection and absorption of electromagnetic wave
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