激光烧蚀金属的真空热电子发射测量  

Vacuum thermal electron emission in pulsed laser ablation on metal surfaces

作　　者：孙克思 袁凤宝 张家良[1] SUN Kesi;YUAN Fengbao;ZHANG Jialiang(School of Physics,Dalian University of Technology,Dalian 116024,China)

机构地区：[1]大连理工大学物理学院,辽宁大连116024

出　　处：《南昌大学学报（理科版）》2022年第2期147-153,共7页Journal of Nanchang University(Natural Science)

基　　金：国家自然科学资助项目(12005087)。

摘　　要：激光烧蚀固体表面开始于激光对表面层的加热,该阶段持续时间极短(与激光脉冲持续时间相当),随即加热层发生熔融、汽化和电离,形成烧蚀等离子体。烧蚀之前表面首先发生热电子发射,形成热发射电子流脉冲。本文以金属Cu、Al、Ti作为靶材,利用Nd:YAG脉冲激光在真空条件下引发烧蚀过程,针对热电子发射设计了一种测量电路,根据电路模型提出了计算热电子流强度的方法,并以此考查了烧蚀热电子发射行为,验证了该测量方法的可行性。该电路基于电流源短路测量原理设计,可以监测热电子流强度的时间演化。文中以热电子流密度的峰值为指标,分析了光斑面积对热电子发射的影响。表明:表面温升过程是决定热电子流密度的主要因素,而激光脉冲能量与光斑面积决定表面温升;当激光能量一定时,热电子流密度随光斑面积增加而迅速减小。根据包括烧蚀区温度及逸出功的热电子发射模型,讨论了三种靶材的烧蚀热电子发射行为,认为逸出功对热发射影响不大,而靶材熔点是热电子发射峰值电流密度的决定因素。As the initial stage of laser ablation on solid surfaces,the phase of heating surface layer lasts for a very short time(order of laser pulse duration)and isthen followed by the process of melting,vaporization and ionization,with ablation plasmas being obtained eventually.Thermal electron emission occurs on the surface before the ablation and formation ofpulsed electron current.Taken as the target metals,Cu,Al and Ti were ablated in vacuum condition using pulsed Nd:YAG laser.We designed a measurement circuit which was capable of tracing the ablation electron emission.According to thecircuit theory,a method was proposed to figure out the electron current intensity.By examining the characteristics of the ablation electron emission,the circuit and the corresponding analysis method was verifiedto be feasible.The circuit was designed based on the shorted measurement,which can monitor the temporal variation of ablation electron emission.By relating the electron emission peak to the laser beam cross-section,it was shown that the surface temperature elevation before ablation determined the thermal electron emission,since the laser energy and thebeamcross-section determined the temperature.If the laser energy was kept constant,the thermal electron current intensity for the 3 targets went down rapidly in a similar way with rising beamcross-section.According to the thermal emission model including the temperature and work function of the ablation zone,it was concluded that the melting point of targets puts heavier effect on the thermal electron emission than the work function.

关 键 词：脉冲激光烧蚀 等离子体 热电子发射 短路测量电路 

分 类 号：O539[理学—等离子体物理]