Triggering and guiding of high voltage discharge by using femtosecond laser filaments with different parameters

This paper demonstrates the triggering and guiding of the stationary high voltage (HV) discharges at 5--40 kV by using plasma filaments generated by femtosecond laser pulses in air. A significant reduction of the breakdown voltage threshold due to the pre-ionization of the air gap by laser filamentation is observed. The discharge experiments are performed by using laser pulses with different energy from 15--60 mJ. The electron density of filaments is detected by sonography method. The influence of the electron density of laser filaments on the triggering and guiding HV discharge is experimentally investigated. The results have shown that the behaviour of plasma filaments can strongly affect the efficiency of triggering and guiding HV discharge.     

双脉冲激光锡等离子体光源的碎屑动力学研究

极紫外光刻是下一代大容量集成电路制造中最有发展前景的技术之一, 而碎屑的减缓及阻挡一直是极紫外光刻光源研究中亟需解决的关键问题。研究了双纳秒激光脉冲辐照锡靶产生的等离子体碎屑的动力学演化。结果表明, 等离子体碎屑强烈依赖于预脉冲的能量及其与主脉冲的时间延迟, 当预脉冲能量为30 mJ, 双脉冲时间间隔150 ns情况下, 大部分锡离子的能量从2.47 keV降低到0.40 keV, 降低了6.1倍, 碎屑得到了有效抑制。通过对碎屑动能角分布的测量, 发现此方法可以有效减缓全角度范围的激光锡等离子体碎屑, 并且越接近靶材法线方向, 碎屑的动能减少得越多。     

Comparative investigation of the resistance and ability to trigger high voltage discharge for single and multiple femtosecond filaments in air

A comparative investigation of the resistance and ability to trigger high voltage(HV) discharge for a single filament(SF) and multiple filaments(MFs) has been carried out.The experimental results show that the trend of the breakdown threshold of the SF exactly follows that of its resistance,but this is not the case for the MF.The MF’s resistance is much smaller than the SF’s.However,the MF shows a slightly higher HV breakdown threshold than the SF.The underlying physics is that the measured resistance of the MF is collectively contributed by every filament in the MF while the HV breakdown threshold is determined by only one single discharging path.     

Influence of Initial Pulse Chirp on Rainbow-Like Supercontinuum Generation from Filamentation in Air

Supereontinuum （SC） generation from laser filamentation in air is found to depend strongly on the pulse duration. Rainbow-like SC generation is observed only for a pulse of appropriate negative chirp that agrees with the predictions put forward by Golubtsov et al. [Quantum Electron. 33 （2003） 525]. The conversion efficiency of an 800-nm laser light to rainbow-like SC is found to be the highest for 257fs pulses with an initial negative chirp. A larger chirp will lead to filamentation surviving at longer distance.     

空气中激光等离子体通道的荧光探测和声学诊断两种方法的比较实验研究

使用荧光探测和声学诊断两种方法，对超强飞秒激光脉冲在空气中传输形成的等离子体通道同时进行了测量.两种方法都很好地反映了等离子体通道的演化过程.对两种方法的比较研究发现，声学诊断相对于荧光探测方法来说，具有较高的灵敏度和空间分辨能力，实验装置也更简单，更适宜于等离子体通道的常规测量. 关键词： 强飞秒激光等离子体通道 荧光探测 声学诊断     

用声学诊断方法测量激光等离子体通道的长度与电子密度

用声学诊断方法对超短脉冲强激光在空气中传输形成的等离子体通道进行了测量，根据通道不同位置的声音信号，得到了通道的长度和通道内电子密度等信息. 关键词： 声学测量 等离子体通道     

空气中单个激光等离子体通道的形成条件

利用皮秒和飞秒激光研究了激光在空气中聚焦产生单个等离子体通道的条件.研究发现，能量为8—12mJ皮秒激光被焦距为15cm的透镜聚焦后，可以产生较为稳定的单个通道.通过横向纵向阴影成像分析发现，通道的管壁对聚焦产生的自发光具有箍缩作用，而通道内部却有利于光的传输.同时还发现，当采用短焦距透镜时，能量低于10mJ的飞秒激光在空气中较易形成单个等离子通道. 关键词： 等离子体通道 皮秒激光 飞秒激光 阴影成像     

空气中飞秒激光等离子体荧光辐射光谱研究

系统地研究了不同聚焦条件下飞秒激光空气等离子体的荧光辐射特性以及空间演化情况.在紧聚焦情况下,由于焦点附近比较高的激光强度以及比较高的电子密度,辐射光谱表现为连续谱和线状原子光谱的叠加.在弱聚焦情况下,辐射光谱主要由很多分子线谱组成,而没有观测到连续谱的产生.还研究了光谱谱线强度随激光传输距离的演化情况,结果显示,光谱谱线的强度变化在一定程度上间接反映了等离子体细丝的演化情况.     

合金钢的激光诱导击穿光谱实验条件优化

利用1 064 nm波长Nd∶YAG脉冲激光诱导击穿合金钢产生激光等离子体光谱,采用高分辨率及门宽控制的ICCD探测LIBS信号光谱。选用铁元素原子谱线404.581,414.387,427.176和438.355 nm进行分析,研究了不同实验参数对LIBS光谱信号强度的影响结果。实验结果表明,激光脉冲能量、激光聚焦位置以及ICCD探测器的延时等实验参数对合金钢LIBS信号有较大影响。通过优化这些实验参数,获得高光谱强度和信背比的LIBS信号,确定了LIBS技术用于合金钢微量元素成分分析的最佳实验条件,从而开展合金钢样品成分分析。     

The polarization characteristics of single shot nanosecond laser-induced breakdown spectroscopy of Al

The polarization-resolved laser-induced breakdown spectroscopy (PRLIBS) technique, which can significantly reduce the polarized emission from laser plasma by placing a polarizer in front of the detector, is a powerful tool to improve the line-to-continuum ratio in LIBS applications. It is shown that the continuum emission from the plasma produced through ablating an Al sample by nanosecond laser pulses is much more polarized than the discrete line emission with the singlepulse PRLIBS technique. The effects of laser fluence and detection angle on the Al polarization spectrum are systematically explored experimentally. The calculated result of the polarization spectrum as a function of laser fluence shows that it is in agreement with the experimental observations.