飞秒激光微加工中诱导空气等离子体的超快观测研究  

Ultrafast observation of air plasma induced by femtosecond laser micromachining

作　　者：王谦豪 杨小君[1] 温文龙[1] 赵华龙[1] 李益 Wang Qianhao;Yang Xiaojun;Wen Wenlong;Zhao Hualong;Li Yi(Photonic Manufacturing System and Application Research Center,Xi'an Institute of Optics and Precision Mechanics,Chinese Academy of Sciences,Xi'an 710119,China;School of Optoelectronics,University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院西安光学精密机械研究所光子制造系统与应用研究中心,陕西西安710119 [2]中国科学院大学光电学院,北京100049

出　　处：《红外与激光工程》2023年第11期13-23,共11页Infrared and Laser Engineering

基　　金：陕西省自然科学基础研究计划项目(2022JQ-473)。

摘　　要：通过搭建飞秒时间分辨的泵浦探测阴影成像系统,研究了聚焦的飞秒激光脉冲产生空气等离子体的瞬态演化特性,并对不同聚焦条件下空气等离子体的时间特性进行了数值模拟。实验结果表明:聚焦的飞秒激光电离空气等离子体的电子瞬态密度峰值先升高后缓慢下降;同时得到了高时间分辨下的电离速度变化与电子数密度的空间分布。计算结果显示:更高的单脉冲能量对应更高的饱和电子数密度,高数值孔径聚焦条件下隧穿电离也更早出现,表明飞秒时间分辨的泵浦探测阴影成像可为超快激光微加工的瞬态过程提供观测手段,同时可对超快激光微加工过程中的等离子屏蔽效应提供机理解释与加工工艺的优化参考。Objective Femtosecond laser micromachining application scenarios commonly occur in atmospheric environments.When the femtosecond laser is focused and interacts with air,it ionizes to produce air plasma,which has a direct impact on the whole machining process.Among other things,the interaction of Kerr selffocusing with plasma scattering leads to filamentation,which changes the light field distribution,and air ionization can significantly affect the laser energy acting on the material.Studying the interaction between femtosecond laser and air,especially the process of ionization of air by laser pulses,is the key to leapfrogging to enhanced applications.To deeply understand the laser micromachining process in atmospheric environment,the transient evolution characteristics of air plasma generated by focused femtosecond laser pulses are studied by building a femtosecond time-resolved pump-probe shadow imaging system,and the temporal characteristics of air plasma under different focusing conditions are numerically simulated.Methods A high time-resolved pump-probe shadow imaging system was built.The laser beam is focused in the air by a microscopic objective and imaged by another laser beam for detection(Fig.1).A 20×microscope objective was used for high-resolution imaging of the plasma to record the time-space evolution of the air plasma.The optical range difference between the pump light and the detection light is adjusted to determine the detection time interval,and the spatial morphology of the air plasma is characterized by the shadow image on the CCD.In the numerical simulation,the ionization model in atmospheric environment is established to obtain the complete process of plasma generation and dissipation in light calling ionization.Results and Discussions Under the microscope focusing conditions at 20×,the plasma is growing and moving rapidly from 0 fs to 59 fs;After 64 fs,it enters a slow evolutionary stage,with the shadow moving speed and propagation distance slowly decreasing;And at 135 fs,the plasma enters

关 键 词：超快激光 等离子体 泵浦探测阴影成像 激光微加工 激光电离 

分 类 号：TN249[电子电信—物理电子学]