飞秒激光诱导气体等离子体产生太赫兹辐射的理论研究

发布时间：2018-03-20 00:01

本文选题：太赫兹气体光子学　切入点：光电流模型　出处：《华中科技大学》2015年硕士论文　论文类型：学位论文

【摘要】：近年来,利用强场激光诱导气体等离子体产生太赫兹辐射的研究吸引了众多科研工作者的关注。与其他产生方法相比,该技术不用考虑介质(气体)的损耗,没有声子共振和吸收,得到的辐射场强度大、光谱范围宽,并且可以利用其原理的逆过程来同时进行探测。本论文基于当前流行的光电流模型,围绕如何获得更高强度和可调制的太赫兹波输出,从改变、调制光场成分以及加入恒定磁场等角度做了一系列的探索。论文首先描述了双色场光电流模型的计算,作为后续研究的理论基础。然后引入三倍频光,并通过模拟计算研究了光束间相位差对辐射强度的影响。通过对特殊值点一个周期光场的具体分析,对三倍频光导致辐射增强给出了一个简单而又物理意义清晰的解释。其次,从改变电子运动的空间对称性出发,研究了加入恒定磁场带来的影响。详细推导了电子在光场和磁场双重作用下速度的离散表达式,并给出了电磁辐射的计算方法。结果表明,加入磁场不但可以增强辐射,还能大大减小相位差的影响,获得比较稳定的输出。最后,从减小光脉冲脉宽和引入线性啁啾两个角度来改变单色光场,探究对低频辐射的影响。啁啾会导致激光频谱向高频和低频方向展宽,而周期量级飞秒激光波形本身就是不对称的,这都会导致太赫兹辐射的增强,并且这两种作用的效果是累积的。另外研究还发现,高频方向的展宽会随着啁啾参数的增大而增大,而低频方向的展宽却呈现一种间歇性起伏的变化趋势。整篇论文通过理论研究发现了几种增强太赫兹辐射的方法,并对结果给出了自己的解释,为将来进一步的理论和实验研究做了基础。
[Abstract]:In recent years, the research on the generation of terahertz radiation from gas plasma induced by a strong field laser has attracted the attention of many researchers. Compared with other generation methods, this technique does not take into account the loss of medium (gas). Without phonon resonance and absorption, the radiation field is large, the spectral range is wide, and the inverse process of its principle can be used to simultaneously detect it. A series of explorations are made on how to obtain higher intensity and modulable terahertz wave output from the angles of changing, modulating the composition of the light field and adding a constant magnetic field. Firstly, the calculation of the photocurrent model of the two-color field is described. As the theoretical basis for further study, the third harmonic light is introduced, and the influence of phase difference between beams on the radiation intensity is studied by simulation. The specific analysis of a periodic light field at a special value point is given. This paper gives a simple and clear explanation of the radiation enhancement caused by triple-frequency light. Secondly, starting from changing the spatial symmetry of electron motion, The influence of the constant magnetic field is studied. The discrete expression of electron velocity under the action of light field and magnetic field is derived in detail, and the calculation method of electromagnetic radiation is given. The results show that the addition of magnetic field can not only enhance the radiation, Finally, the monochromatic light field can be changed by reducing the pulse width and introducing the linear chirp. To explore the effects on low frequency radiation. Chirp results in the broadening of the laser spectrum in the high and low frequency directions, while the periodic femtosecond laser waveform itself is asymmetrical, which leads to the enhancement of terahertz radiation. Moreover, the effects of these two actions are cumulative. In addition, it has been found that the broadening of the high frequency direction increases with the increase of chirp parameters. However, the broadening of low-frequency direction shows a tendency of intermittent fluctuation. In this paper, several methods of enhancing terahertz radiation are found through theoretical research, and the results are explained. It provides a basis for further theoretical and experimental research in the future.
【学位授予单位】：华中科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN24

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