飞秒等离子体间非线性作用对超高频电磁波影响的研究

主要研究了飞秒等离子间相互的非线性作用对超高频电磁波——太赫兹波产生的影响。国内外许多研究机构已经证实，在太赫兹波产生的过程中，等离子体间的相互非线性作用会对太赫兹波产生影响。笔者结合理论分析设计并搭建一种了双束等离子体重合产生太赫兹波的测试系统，研究发现等离子体间相互非线性作用时，会产生三阶非线性光学效应，等离子体的折射率和相位发生变化形成非均匀场导致了太赫兹波辐射能量的降低，并在实验测量研究中发现随着等离子体波长双束等离子波长的增加，等离子体密度增加，导致太赫兹波的辐射能量的降低现象更加明显，另外，等离子体功率越大，太赫兹波吸收越大。同时，研究发现等离子体周围惰性气体分子质量影响太赫兹降低程度，气体分子质量决定着飞秒激光聚焦空气电离出的等离子体所形成的电场强度，分子质量越高，所形成的电场强度越强，双束等离子体重合时对太赫兹波降低的辐值越大。这些为研究等离子体间非线性作用对太赫兹波的影响提供了更加全面的理论支撑，有助于推动太赫兹波技术在军事及民用领域的快速发展。

Influence of nonlinear interaction between femtosecond plasmas on ultra-high frequency electromagnetic waves

The influence of the nonlinear interaction between femtosecond plasmas on the ultra-high frequency electromagnetic wave—terahertz (THz) wave was mainly studied in this paper. Many research institutions had confirmed that in the process of generating THz wave, the interaction between plasmas would affect THz wave. Combined theoretical analysis, a test system for generating THz wave due to the coincidence of two-beam plasmas was designed by the author. The study found that the nonlinear interaction between plasmas will produce a third-order nonlinear optical effect. The refractive index and phase of the plasma changed to form a non-uniform field, which led to a decrease in the radiant energy of the THz wave. In the experimental measurement research, it was found that with the increase of the plasma wavelength of the double beam plasma wavelength, the plasma density increased, resulting in a more obvious decrease in the radiation energy of the THz wave. In addition, the greater the plasma power, the greater the absorption of THz wave. At the same time, it was found that the mass of inert gas molecules around the plasma affected terahertz reduction degree. The mass of gas molecules determined the intensity of the electric field formed by the plasma ionized by the femtosecond laser focusing on the air. The higher the molecular mass, the stronger the intensity of the electric field formed, and the greater the magnitude of the THz wave reduced when the two-beam plasma overlapped. The study provides more comprehensive theoretical support for influence of the nonlinear interaction between plasmas on the THz wave, which helps to promote the rapid development of THz wave technology in the military and civilian fields.