飞秒光丝诱导空气反波导中的激光成丝及其控制研究

Filamentation formed by powerful femtosecond laser pulse in air leaves behind a long-lived low-density channel which has a low-refractive index core surrounded by a higher index of refraction. It can be called anti-waveguide due to its inverse refraction index distribution of optical fibers, and will have a defocusing effect on the subsequent laser. In this project, we propose for the first time to optimize and control the filamentation by introducing the anti-waveguide. A new dynamic balance among Kerr self-focusing, defocusing by plasma and the anti-waveguide will be under control by adjusting the participation degree of the anti-waveguide, resulting in optimization and control of the filamentation and supercontinuum (SC) generation. We will study systematically key scientific issues including the influences of the anti-waveguide on the filamentaion and SC generation, based on the temporal evolution and spatial distribution of the anti-waveguide, which has not been reported up to now. The implementation of this project will enable us to understand the underlying physics and establish the method of the filamentation and SC generation optimization and control by the introduction of the anti-waveguide, and contribute to many potential applications of the filamentation and SC generation.

超强飞秒激光脉冲在空气中成丝传输后的毫秒时间量级内，成丝路径上会形成一个与光纤折射率分布相反的低密度通道，称为空气反波导，该反波导折射率分布对激光具有散焦效应。本项目首次提出将该反波导结构引入到后续飞秒激光的非线性成丝过程中，通过控制其介入程度以调控激光成丝过程中克尔自聚焦、等离子体散焦以及由该结构引入的散焦作用等非线性效应间的动态平衡，实现激光成丝及其超连续辐射的优化控制。本项目在掌握该反波导结构折射率的时间演化及空间分布规律的基础上，重点研究反波导结构对激光成丝过程及其超连续辐射的影响规律和物理机制，该项工作在国际上尚无报道。通过本项目的实施，将掌握反波导结构对激光成丝及其超连续辐射优化控制的物理机制，获得激光成丝优化控制的新方法，为激光成丝应用提供理论基础及技术手段。

飞秒激光在空气中的长距离成丝传输有着重要的应用前景，如激光遥感、诱导闪电和定向能等应用。面向这些远距离应用的要求，需要对飞秒激光成丝的特征进行控制和优化。本项目通过实验和理论研究了飞秒激光成丝诱导产生的空气反波导结构对后续激光成丝过程及超连续辐射的影响，揭示了飞秒激光在空气反波导结构中传输的成丝过程和超连续辐射的演化规律以及相应的物理机制。完成了项目的研究计划，并取得了多项创新性研究成果。. 理论研究了空气反波导的长度、位置、时间延迟以及纵向和横向偏移对后续激光成丝和超连续辐射的影响规律；实验研究了不同空间间隔和时间延迟的反波导结构对后续激光成丝及超连续辐射的影响，实现了对成丝起点和长度的调控。结合理论和实验结果，揭示了反波导结构对激光成丝及超连续辐射影响的物理机制；研究了激光重复频率对反波导结构控制成丝及超连续辐射的影响。. 本项目的完成为优化控制激光成丝提供了新方法，为激光成丝的相关应用提供了物理基础和技术手段。