【作者】 杨旋；

【导师】 徐至展； 曾和平；

【作者基本信息】 华东师范大学 ， 光学， 2010， 博士

【摘要】 超短强激光脉冲在空气介质中传播时,由于空气的非线性克尔自聚焦效应和等离子体的自散焦效应之间的动态平衡,将在空气中形成类似波导传输的光丝通道,具有能量稳定和单模光斑的优点。但是,由于实验条件以及环境的印象,光丝若想实现类似波导的远距离传输,需要非常高的激光功率和稳定的大气环境,这一因素大大限制了其应用的广泛性。近年来研究发现,光丝间的非线性强相互作用可用于调控光丝的传播过程,保持其能量稳定传输的同时有效增长其传播距离；另外,期间产生的三次谐波能量也将随之大幅提高。这对于强激光脉冲的长距离传输和紫外光源的开拓发展都将有着重要的实际应用意义。本论文以飞秒光丝为研究对象,针对光丝间的强相互作用,对光丝传播过程、三次谐波能量转化效率提高以及所产生的多维波导效应进行了详细研究。具体的工作可分为以下几个部分：1.将光丝间的强相互作用应用到对光丝传播距离的控制中,实现了飞秒光丝传输距离的有效延长和三次谐波能量转换效率的大幅提高(约两个数量级)。实验中,通过改变非共线光丝的夹角、强度对比度以及相对偏振关系等实验参数,可以有效调控三次谐波的能量转化过程。此外,这一技术也可应用于周期量级飞秒激光的成丝过程,有效实现宽带三次谐波能量的增强。这一结果对紫外波段周期量级飞秒激光脉冲的获得提供了新型有效的方法。2.通过调节光丝相互作用区域处的时间空间重合,获得了波长量级的等离子体通道阵列的形成。实验中,通过调节飞秒光丝间的非共线结构,可以有效调节等离子体通道芯径的大小及其空间分布,使其出现类似于光子晶体光纤的分布结构。该分布结构可用于引导更高峰值功率强脉冲激光的传播,为新型等离子体波导的实现奠定基础。3.利用飞秒光丝干涉诱导产生的自引导通道,形成具有光栅结构的周期性折射率分布,实现了一维和二维等离子体密度调制的动态光栅。实验中,通过改变相互作用的飞秒脉冲的偏振关系及强度对比,测量对应的光栅参数,获得了二次和三次谐波的衍射角及衍射能量的变化,最终确定了激光脉冲参数与动态光栅的对应关系,为后期动态光栅的实际应用奠定了基础。更多还原

【Abstract】 Self-guided propagation of ultrashort intense laser pulses in air is demonstrated to induce filament channels with the advantage of energy-stability and high-quality beam profile due to the counterbalance between Kerr self-focusing and plasma-defocusing. However, filament can not be functioned as waveguide to keep energy propagate in a long distance due to the influence of experimental condition and environment. Therefore, the application of filament is limited by these factors. Recently, two-beam interaction is considerate as an efficient candidate process for the filament control to elongate the filament distance. In addition, the third harmonic generation is also enhanced. It will be beneficial to the laser long-distance propagation and the development of UV laser.With filament as the research object, this thesis is mainly focused on influence of the strong interaction between filaments on the filament propagation, enhancement of third harmonic energy conversion and the effect of multi-dimension waveguide. Mainly include the following:1. The filament control is achieved in the way of filament interaction to fulfill the elongation of filament and the two-order enhancement of third harmonic energy conversion. In the experiment, the process of third harmonic generation could be controlled by changing the noncollinear crossing angles, input intensity ratios, and input pulse polarizations. In addition, this technology can also be applied to the filamentation process of few-cycle pluses to fulfill the enhancement of broadband third harmonic. It provides a new and effective way to achieve the few-cycle femtosecond laser pulse in UV domain.2. The wavelength-scale periodic plasma waveguide array is achieved by adjusting the spatiotemporal overlap of laser pulse in the filament interaction region. The diameter and spatial distribution of plasma waveguide array can be adjusted by changing the non-collinear structure of incident filaments and creates the structure similar as that of photonic-crystal fiber. The results can be used to guide the laser pulse with high peak intensity and makes the foundation for the creation of novel plasma waveguides.3. Based on the formation of interference-assisted self-guide channel, the periodical refractive index distribution is formed in the interaction region and fulfills the 1-and 2-Dimensional plasma dynamic gratings in air. Experimentally, the parameters of grating and variation of energy diffraction of second and third harmonics is measured by changing the relative polarization and intensity ratio of the incidence pulses. Based on the results, we find the relation between the formation of dynamic gratings and the parameters of laser pulse and make the foundation for the practical application of dynamic grating.更多还原