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摘 要：气体介质中的强飞秒激光会产生一些独特现象，这引发了科研工作者的关注。在空气这种非线性克尔介质中传输的飞秒激光由于其非线性效应会形成长长的光丝，成丝的过程中会包含许多的现象比如自聚焦、衍射、等离子体散焦等。飞秒激光成丝现象中也蕴含着许多潜在的应用价值，例如基于等离子体通道的诱导闪电、基于自相位调制的激光雷达、基于光丝长距离传输特性的大气污染探测和基于飞秒激光丝強电离的人工降雨。38537
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本文叙述了飞秒激光在空气中的传输特性，并推导了飞秒激光在空气中的传输方程。文章主要由四章内容组成：
第一章，我们叙述了飞秒激光的发展史以及飞秒激光在空气中的传输特性，并详细描述了飞秒激光成丝的一些应用。
第二章，我们对空气中飞秒成丝的相关现象进行了详细的描述，如自聚焦、自相位调制、等离子体散焦，并对飞秒成丝的三种主要理论模型移动焦点模型、自导引模型、动态空间补偿模型进行了综述。
第三章，飞秒激光在空气中传输时会受到多种非线性效应的影响，其中最主要的是非线性克尔效应以及等离子体散焦。我们从飞秒激光在空气中的传输方程出发，以Sprangle等人的模型为基础，结合非线性克尔效应以及等离子体散焦这两方面，推导了我们所需要的飞秒激光在空气中的传输模型。此外，我们仿真了飞秒激光的基模高斯光束在不同位置处的光强。
第四章，我们对本文做了总结概括并列举了本论文中的不足点，比如在推导传输的方程时我们并没有把所有的非线性因素考虑进去，简化了求解过程，模型的完整度上有待完善。
毕业论文关键词：飞秒现象 自聚焦 非线性光学
Characteristics and research of femtosecond laser pulses propagating in air
Abstract：High-intensity femtosecond laser has caused the concern because it shows some particular phenomena in gases .When a femtosecond laser pulse propagates in air,filament will be formed because of nonlinearities, which is the well-known filamentation process and makes the long distance propagation. When a femtosecond laser propagates in air,there are many phenomena in the process such as self-focusing, plasma defocusing, diffraction, etc.There are many promising applications in filamentation such as inducing of lightning, laser radar, detection of air pollutants, artificial rainfall.
This paper narrated the transmission characteristics of femtosecond laser,and we deduced the equation of femtosecond laser propagating in air .The paper consists of four chapters.
In the first chapter, we narrated the history of the development of femtosecond laser and the characteristics of femtosecond laser.Then we described some applications of filaments .
In the second chapter, we described some phenomena of femtosecond filamentation in air.And we reviewed three theoretical models to describe femtosecond filamentation.
In the third chapter, femtosecond laser is effected by many nonlinearities. Kerr effect and plasma defocusing are the most important effects.We deduced the equation of femtosecond laser propagating in air based on the Sprangle’s model and took Kerr effect and plasma defocusing into consideration. Then we simulated the intensity of base mode Gauss beam of femtosecond laser.
In the fourth chapter, we summarized the paper and listed some shortcomings such as when deducing the equation ,we did not think of all nonlinearities and simplified the process.
Keywords: femtosecond phenomena self-focusing nonlinear optics
目 录
摘 要 I
Abstract II
0.绪论 1
1.飞秒激光成丝现象及成丝应用 2