飞秒激光在空气中成丝诱导氮荧光发射的空间分布  

Spatial distribution of nitrogen fluorescence emission induced by femtosecond laser filamentation in air

作　　者：张云 林爽 张云峰 张鹤[1,2] 常明莹 于淼 王雅秋 蔡晓明 姜远飞 陈安民[1,2] 李苏宇 金明星[1,2] Zhang Yun;Lin Shuang;Zhang Yun-Feng;Zhang He;Chang Ming-Ying;Yu Miao;Wang Ya-Qiu;Cai Xiao-Ming;Jiang Yuan-Fei;Chen An-Min;Li Su-Yu;Jin Ming-Xing(Institute of Atomic and Molecular Physics,Jilin University,Changchun 130012,China;Jilin Provincial Key Laboratory of Applied Atomic and Molecular Spectroscopy,Jilin University,Changchun 130012,China;Changchun Institute of Optics,Fine Mechanics and Physics,Chinese Academy of Sciences,Changchun 130033,China)

机构地区：[1]吉林大学,原子与分子物理研究所,长春130012 [2]吉林大学,吉林省应用原子分子光谱重点实验室,长春130012 [3]中国科学院长春光学精密机械与物理研究所,长春130033

出　　处：《物理学报》2021年第13期123-129,共7页Acta Physica Sinica

基　　金：国家重点基础研究发展计划(批准号:2019YFA0307701);国家自然科学基金(批准号:11704145,11974138,11674128,11504129,11674124);吉林省教育厅“十三五”科学研究规划项目(批准号:JJKH20190181KJ)资助的课题.

摘　　要：测量了线偏振飞秒激光脉冲在空气中成丝产生的氮荧光发射的空间分布.通过改变激光的偏振方向研究成丝过程中氮荧光发射的径向角分布,发现N_(2)^(+)荧光发射在垂直于激光偏振方向上更强,而在平行于激光偏振方向上较弱;N2荧光发射在所有方向上具有近乎相同的强度.原子和分子的激发、电离等动力学过程受激光强度的影响.在飞秒激光成丝过程中沿着激光传播方向,强度呈现先增强后减弱的分布,从而影响这些过程的产物的空间分布及其荧光发射的空间分布.沿着激光传播方向,发现N2荧光先于N_(2)^(+)荧光出现且在N_(2)^(+)荧光消失之后消失.激光强度分布和激光偏振方向均会影响氮荧光的空间分布.基于实验分析,在短焦距情况下,系间窜越过程能很好的解释N2(C^(3)Ⅱ_(u)^(+))的形成,这项研究有助于理解飞秒激光成丝过程中氮荧光发射的产生机制.As a major component in the air,nitrogen emits fluorescence when it interacts with intensive laser field.The fluorescence comes from the first negative band system(B^(2)∑_(u)^(+)→X2∑g+transition)of N_(2)^(+)and the second positive band system(C^(3)Ⅱ_(u)^(+)→B3Ⅱg+transition)of N_(2).Under the action of high-intensity femtosecond laser,N_(2) can be directly photo-ionized intoN_(2)^(+)(B^(2)∑_(u)^(+)),which results in fluorescence emission of N_(2)^(+).In the process of femtosecond laser filament formation,the dynamic processes such as ionization and excitation of nitrogen molecules are affected by the laser intensity distribution and laser polarization direction.The products show different distributions in the propagation direction and radial space,which,in turn,affects its light emission.Therefore,it is necessary to further ascertain its generation mechanism through the spatial distribution of nitrogen fluorescence.In this experiment,the spatial distribution of the nitrogen fluorescence emission generated by linearly polarized femtosecond laser pulse filaments in air is measured.By changing the polarization direction of the laser to study the distribution of nitrogen fluorescence in the radial plane,it is found that the fluorescence emission of N_(2)^(+)is more intense in the direction perpendicular to the laser polarization,while it is weaker in the direction parallel to the laser polarization.The nitrogen fluorescence emission has the same intensity in all directions.The ionization probability of a linear molecule depends on the angle between the laser polarization direction and the molecular axis,which is maximum(minimum)when the angle is 0°(90°).The gas is more likely to be ionized in the laser polarization direction,the nitrogen molecular ions and electrons are separated in the direction parallel to the laser polarization.Therefore,more ions(N_(2)^(+))are generated in the direction parallel to the laser polarization,and the fluorescence emission of N_(2)^(+)is more intense.Along the propagatio

关 键 词：飞秒激光脉冲 飞秒激光成丝 氮分子 荧光 

分 类 号：TN249[电子电信—物理电子学]