超快高强度激光脉冲在空气中的传输与相互作用的研究
文献类型：学位论文
| 作者 | 段作梁 |
| 学位类别 | 博士 |
| 答辩日期 | 2004 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 徐至展 |
| 关键词 | 飞秒高强度激光脉冲 自聚焦 自波导 等离子体细丝通道 成丝作用 |
| 其他题名 | Study on Propagation of Ultrafast High-intensity Laser Pulses in Air and Their Interaction |
| 中文摘要 | 近年来，随着飞秒激光技术的发展，超快高强度激光脉冲在空气中的传输与相互作用的研究展现出非常广阔的应用前景。飞秒高强度激光脉冲在透明介质（固体，液体和气体）中传输时引起介质的高阶非线性效应，导致介质折射率的改变，从而极大地影响了激光束在透明介质中的性质。飞秒高强度激光脉冲在空气中传输形成长的等离子体通道具有广泛的应用，诸如产生超连续谱白光、大气污染的监测，人工诱雷放电、激光等离子体天线、一匕秒脉冲高次谐波的生成等。飞秒高强度激光在空气中的传输与相互作用是研究是超快高强度激光物理领域的重要研究课题，也是当前飞秒高强度激光应用领域的研究热点之一，它涉及到大气中各种激光电离机制、非线性传输效应等问题的研究，其成果具有重要的科学意义和广泛的应用前景。本论文开展了飞秒高强度激光脉冲在大气中传输中出现自聚焦、等离子体通道形成、多光子电离和等离子体散焦等非线性效应的研究，并以实现在大气中产生长的等离子体通道为目标，为等离子体激光天线和激光诱雷放电等应用提供了重要的实验依据。本论文主要取得了以下几点创新性的成果：1．首次提出并使用纵向衍射干涉的方法测量出等离子体细丝通道的直径和通道中电子的平均密度。从等离子体细丝通道中电子密度在时域的演化过程中，发现电子密度可以维持的特征时间是纳秒（ns）量级。2．在实验上研究飞秒高强度激光脉冲在空气中传播形成等离子体细丝通道的特征和现象。通过记录成丝过程中不同位置处激光脉冲径向上光强分布，观测到飞秒激光脉冲先形成双丝，然后合并成单丝；以及通道中细丝的形状影响三次谐波空间截面上的光强分布，这样通过三次谐波的空间分布能够反推出等离子体通道的空间结构。3．使用本实验室研制的23太瓦（TW）钦宝石超短超强激光系统研究了高能量的飞秒激光脉冲在空气中传播形成等离子体细丝通道的特点。观测到多丝结构的形成，同时发生强的锥形辐射，并通过锥形辐射图样发现空气中分子密度的起伏对高能量的激光脉冲成丝影响很大。这些实验结果对以后的应用中如何选择合适的激光脉冲能量产生细丝通道提供了实验依据。4．使用本实验室研制的小型化光学参量惆啾脉冲放大（optical parametricchirped pulse amnlififation，OPCR）的超短超强激光装置，首次研究了飞秒级1064nm倍频光束在水中的传输特性。观测到倍频光在水中传播导致自聚焦效应，发现形成了相当于10倍瑞利长度的自波导传播。通过观钡（倍频光在水中传播到不同位置处径向上光强的分布情况获得倍频光的成丝演化过程；以及通过观测倍频光在水中传播方向上光强的分布研究了倍频光在水中传播形成多个自聚焦焦点的现象。 |
| 英文摘要 | Recently, with the development of the femtosecond laser technology, the research on the propagation of ultrafast high-intensity laser pulses in air and their interaction shows a promising future. Femtosecond high-intensity laser pulse leads the high-order nonlinear effects and the refractive index change of the media while it propagates in transparent media (solid, liquid and gas), which impact tremendously the laser beam characteristics in transparent media. The plasma channel formed by the propagation of femtosecond high-intensity laser pulse in air has extensive applications, such as supercontinuum light generation, inspection of the atmosphere pollution, triggering lightning, Lidar, femtosecond high-order harmonic generation and so on. The research on the propagation of the femtosecond high-intensity laser pulses in air and their interaction is a topic of intense research activities in the field of the ultrafast high-intensity laser physics, and one of the hot researches on the application of the femtosecond high-intensity laser pulses. It is involved with the researches of the laser ionization mechanics, nonlinear transmission effect and so on. The results of the research have a great significance and the extensive application prospect. In this dissertation, the propagation of femtosecond high-intensity laser pulse in air involving self-focusing, plasma channel, multiphoton ionization and plasma defocusing have been investigated. The research target is to produce a long filament. And the results provide the important experiment foundation of the applications on Lidar, triggering lightning and so on. This thesis includes mainly the following new results: 1. With the longitudinal diffraction interferometry for the first time, the diameter of the plasma channel and the electron density have been measured in the plasma channel. The characteristic time of the electron density lasting in the plasma channel is about nanosecond order from the temporal evolution of the electron density in the plasma channel. 2. Experimentally the characteristics and the phenomena of the plasma channel formed by the femtosecond high-intensity laser pulses propagating in air and evolution of filament have been investigated. The transverse intensity distributions of the laser pulses at the different position in the filament process have been measured, it is found that the two-filaments form at first and then merge into a single one. And the shape of the plasma channel determines the transverse distribution of the laser intensity of the third-harmonic, whereas the spatial configuration of the filament can be deduced through the transverse distribution of the laser intensity of the third-harmonic. 3. The characteristics of the plasma channel formed by the femtosecond high-power laser pulse propagating in air have been investigated with the homemade 23 TW Ti:sapphire laser system in our lab. The characteristics include the formation of the multi-filament, intensive conical emission and the immense influence of femtosecond high-power laser pulse forming filament from the density fluctuation of air through the picture of the conical emission. The results are beneficial for choosing the proper laser energy of producing filament in the future application. 4. For the first time the characteristics of the second-harmonic of 1064nm femtosecond laser pulses propagating in water have been investigated with the homemade optical parametric chirped pulse amplification(OPCPA) laser system in our lab. The experimental evidences showing the self-focusing formed by the second-harmonic propagation in water have been found, and the self-guided propagation exceeding 10 times Rayleigh length. The evolution of the filament of the second-harmonic have been investigated through the observation of the transverse intensity distribution of second-harmonic propagating at different place in water, and the characteristics of multi-focuses of self-focusing formed by the second-harmonic propagating in water through analyzing the longitudinal distribution of light intensity. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15565]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 段作梁. 超快高强度激光脉冲在空气中的传输与相互作用的研究[D]. 中国科学院上海光学精密机械研究所. 2004. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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