等离子体通道的声学诊断方法

超短脉冲强激光在空气中传输可以形成很长的等离子体通道，目前对这种等离子体通道有许多诊断方法，文章介绍了一种十分简易但很有效的方法——声学测量方法．该方法可以根据通道不同位置的声音信号，测量通道的长度和通道内电子密度等一些参数，具有其他传统诊断方法无可比拟的优越性．     

靶结构对激光等离子体动量耦合系数的影响

强激光与靶相互作用产生的等离子体可以作为一种新型的推进源.就强激光与靶相互作用过程中，靶结构对激光等离子体动量耦合系数的影响进行了研究.结果表明，相对于无约束的平面靶，坑靶将动量耦合系数提高了5倍，而约束的平面靶将动量耦合系数提高了10倍以上.分析发现，对等离子体的有效约束是提高动量耦合系数的主要原因. 关键词： 激光等离子体 推进 动量耦合系数     

Effect of the target positions on the rapid identification of aluminum alloys by using filament-induced breakdown spectroscopy combined with machine learning

Filament-induced breakdown spectroscopy (FIBS) combined with machine learning algorithms was used to identify five aluminum alloys. To study the effect of the distance between focusing lens and target surface on the identification accuracy of aluminum alloys, principal component analysis (PCA) combined with support vector machine (SVM) and K-nearest neighbor (KNN) was used. The intensity and intensity ratio of fifteen lines of six elements (Fe, Si, Mg, Cu, Zn, and Mn) in the FIBS spectrum were selected. The distances between the focusing lens and the target surface in the pre-filament, filament, and post-filament were 958 mm, 976 mm, and 1000 mm, respectively. The source data set was fifteen spectral line intensity ratios, and the cumulative interpretation rates of PC1, PC2, and PC3 were 97.22%, 98.17%, and 95.31%, respectively. The first three PCs obtained by PCA were the input variables of SVM and KNN. The identification accuracy of the different positions of focusing lens and target surface was obtained, and the identification accuracy of SVM and KNN in the filament was 100% and 90%, respectively. The source data set of the filament was obtained by PCA for the first three PCs, which were randomly selected as the training set and test set of SVM and KNN in 3:2. The identification accuracy of SVM and KNN was 97.5% and 92.5%, respectively. The research results can provide a reference for the identification of aluminum alloys by FIBS.     

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.     

Double Jet Emission of Hot Electrons from a Micro-droplet Spray

Spatial distribution of hot electrons with energies above 50 keV are investigated by an ethanol micro-droplet spray irradiated by linearly and elliptically polarized 150 fs laser pulses at an intensity of 10^18 W/cm^2. Two symmetric hot electron jets with respect to the laser propagation direction are observed in the polarization plane for a     

飞秒激光引导闪电的模拟实验研究

采用能量40 mJ，脉冲宽度50 fs的超短脉激光脉冲形成的等离子体通道诱发和引导了3—23 cm长间隙的静态高压放电.实验观测显示，等离子体通道整体上能使空气间隙的击穿阈值降低到自然击穿阈值的40％.实验中通过对放电电弧发出的白光信号与激光信号的时间延迟进行分析得到激光引导下梯级先导的发展速度约为10⁷ cm/s. 关键词： 等离子体通道 高压放电     

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。     

飞秒平顶光束经微透镜阵列在熔融石英中的成丝及其超连续辐射

实验研究了平顶激光光束经微透镜阵列在熔融石英中成丝的演化以及超连续辐射的产生,并进一步与高斯光束的成丝和超连续辐射进行了对比研究.分别对这两种光束的多丝传输进行了横向和纵向成像.结果表明,使用平顶光束可以获得更为均匀的多丝分布,成丝的起点也更为一致;尤其重要的是,相对于高斯光束,平顶光束可以使用更高的入射激光脉冲能量而不会造成介质的损伤,从而可以获得更高脉冲能量和更高转换效率的超连续辐射.     

整形飞秒激光脉冲的成丝超连续辐射控制

飞秒激光成丝超连续辐射具有高强度和高时空相干性等优点,作为一种超宽带光源在很多领域都具有广泛的应用前景.本文提出一种结合微透镜阵列的空间调制和基于液晶空间光调制器的时域整形的飞秒激光脉冲整形方式,利用基于遗传算法的反馈优化控制,实现了飞秒激光在熔融石英中成丝产生的超连续辐射强度的调制,得到了在一定范围内光谱强度可控的超连续辐射光谱;光谱的能量密度可以从0.03μJ/nm调制到0.09μJ/nm,其能量密度变化达到了初始值的3倍.计算了典型迭代代数对应的整形脉冲时域包络,分析了超连续光谱随迭代代数的演化趋势,结果表明,脉冲包络的峰值强度和波形分布是影响超连续光谱展宽和强度的主要物理原因.     

The high dependence of polarization resolved laser-induced breakdown spectroscopy on experimental conditions

It is shown that the continuum emission produced by an Al alloy ablated by femtosecond laser pulses is much more polarized than the characteristic lines of elements. A Glan-Thomson polarizer is used in the laser-induced breakdown spectroscopy experiment to investigate the polarization effect. The use of the polarizer at its minimal transmission increases the signal-to-noise ratio. The effects of angle of detection, focal position, and pulse energy on the signal-to-noise ratio are also studied.