Emission analysis of expanding laser produced lithium plasma plume in presence of ambient gas

Atomic analysis of the emission from laser-produced plasma from bulk lithium (Li) block has been made. The observed changes in the emission from lithium neutral and ionic species have been explained by considering various atomic processes. We demonstrate that the excitation process in case of neutral lithium Li (I) is electron impact excitation whereas for singly ionized lithium Li (II), radiative recombination is the dominant mechanism. We also show that the ionized species are dominant in the LPP plume.     

吸积盘的X射线辐射对周围星际物质的离化研究

利用辐射流体力学程序对三倍频纳秒激光与靶物质相互作用进行了模拟研究，得到了可以产生黑体辐射谱分布的激光等离子体X射线辐射靶的最佳厚度；数值模拟研究了黑体谱分布的X射线辐射场对等离子体系统平均离化度分布的影响，它有助于深入理解天体物理中吸积盘对它周围星际物质的离化影响. 关键词： 辐射流体力学 激光等离子体 X射线辐射 吸积盘 离化     

Resonance processes during harmonic generation in plasmas using mid-infrared radiation

A few recently introduced approaches of the high-order harmonic generation in laser-produced plasmas are reviewed. We show how the tuning of odd and even high-order harmonics of ultrashort pulses along the strong resonance of laser-produced indium plasma using optical parametric amplifier of white-light continuum radiation (1250?1400 nm) allows observation of different harmonics enhanced in the vicinity of the transition of In II ions possessing high oscillator strength. We discuss various peculiarities and discuss the theoretical model of the phenomenon of tunable harmonics enhancement in the region of 62 nm using indium plasma. With the theoretical analysis, we present the approach allowing reproduce the experimental observations and characterize the dynamics of the resonant harmonic emissions. We also discuss the resonance enhancement of harmonics using mid-infrared radiation in the tin, chromium, and antimony plasmas and show the calculations of this process.     

Bi靶激光等离子体极紫外光源以及碎屑辐射特性研究

激光等离子体极紫外光源具有体积小、稳定性高和输出波长可调节等优势,在极紫外光刻领域发挥着重要的作用。Bi靶激光等离子体极紫外光源在波长9～17 nm范围内具有较宽的光谱,可应用于制造极紫外光刻机过程中所需的极紫外计量学领域。利用平像场光谱仪和法拉第杯对Bi靶激光等离子体极紫外光源以及离子碎屑辐射特性进行了实验研究。在单脉冲激光打靶条件下,实验中观察到Bi靶激光等离子极紫外光谱在波长12.3 nm处出现了一个明显的凹陷,其对应着Si L-edge的吸收,是Bi元素光谱的固有属性。相应地在波长为11.8和12.5 nm位置处产生了两个宽带的辐射峰。研究了两波长光谱特性以及辐射强度随激光功率密度的变化。结果表明,在改变聚焦光斑大小实现不同激光功率密度（0.7×1010～3.1×1010 W·cm-2）过程中,当功率密度为2.0×1010 W·cm-2时两波长处的光辐射最强,其原因归结为Bi靶极紫外光辐射强度受激光能量用于支撑等离子膨胀的损失和极紫外光被等离子体再吸收之间的平衡制约所致。在改变激光能量实现不同激光功率密度过程中,由于烧蚀材料和产生两波长所需高阶离子随着功率密度的增加而增加,增强了两波长处的光辐射。进一步,研究了双脉冲激光对Bi靶极紫外光谱辐射特性影响,实验发现双脉冲打靶下原来在单脉冲打靶时出现在波长13～14 nm范围内的凹陷消失。最后,对单脉冲激光作用Bi靶产生极紫外光源碎屑角分布进行了测量。结果表明,当探测方向从靶面法线方向移动到沿着靶面方向上的过程中,探测到Bi离子动能依次减小,并且离子动能随激光脉冲能量降低而呈线性减小。此项研究有望为我国在研制极紫外光刻机过程所需的计量学领域提供技术支持和打下夯实的基础。     

Spatial resolution of X-ray line emission in laser produced plasma by shadow techniques

Spatial resolution of X-ray emission from laser-produced plasmas is obtained by placing a 500 μm wire between the plasma and a slitless crystal spectrometer. The sizes of emitting regions of various spectral lines, as well as electron temperature and density spatial profiles are deduced for an Al plasma.     

微通道板X射线探测器

在激光等离子体实验研究中,为了更好地了解激光与等离子体相互作用过程中所发生的物理过程,要求能够高时间分辨地观测等离子体所辐射的X射线的特征。测量的关键在于X射线探测元件,既要有快的时间响应,又要能够输出足够大的光电流,以便直接驱动高速示波器,进行显示和照像。普通的闪烁体/光电倍增管X射线探测器,由于闪烁体荧光有着固有的衰减时间,以及普通的光电倍增管中的电子飞行时间离散严重,时间分辨力难以提高。     

超声波辅助提取-HG-ICP-AES法测定中草药雷公藤中可溶态Sb(Ⅲ)和Sb(Ⅴ)

本文建立了用超声波辅助提取,氢化物发生-电感耦合等离子体原子发射光谱法测定中草药雷公藤中可溶态Sb(Ⅲ)和Sb(Ⅴ)的分析方法。研究了超声波辅助提取的影响因素、锑形态分离的最佳pH值、仪器工作条件对锑氢化物发生的影响及五价锑的还原条件,探讨了共存离子对锑测定的干扰及消除方法。Sb(Ⅲ)和Sb(Ⅴ)的检出限分别为0.3和2.4 μg·L-1, 相对标准偏差分别为3.9%和4.5%,样品加标回收率为93%～105%。     

Numerical simulation of melting and evaporation of a cold foil target irradiated by a pre-pulse

Melting and evaporation of matter due to pre-pulse irradiation of a high-peak-power ultra-short pulse laser onto a cold foil target and the expansion of laser-produced plasma are numerically evaluated using a hydrodynamic code based on CIP (cubic-interpolated propagation) and modified C-CUP (CIP-combined unified procedure) methods. The material properties of the solid, equation of state, laser absorption coefficient, skin depth, and thermal conductivity are consistently implemented. The formation and propagation of laser-produced plasmas are obtained with good numerical stability. PACS 02.70.-c; 52.38.Mf; 52.38.Kd     

Temporally and spectrally resolved imaging of laser-induced plasmas

We report a hybrid imaging technique capable of performing measurements of the spatial, temporal, and spectral emission characteristics of laser-induced plasmas by use of a single detection system. We apply this technique to study the plasma produced by laser ablation of LiNbO3 and observe phenomena not seen in such detail with standard instruments. These include extreme line broadening up to a few nanometers accompanied by self-absorption near the target surface, and expansion dynamics that differ strongly between the different species. Overall, the wealth of quantitative information provided by this novel technique sheds new light on processes occurring during plasma expansion.     

Effect of dielectronic recombination on the charge-state distribution and soft X-ray line intensity of laser-produced carbon plasma

The effect of dielectronic recombination in determining charge-state distribution and radiative emission from a laser-produced carbon plasma has been investigated in the collisional radiative ionization equilibrium. It is observed that the relative abundances of different ions in the plasma, and soft X-ray emission intensity get significantly altered when dielectronic recombination is included. Theoretical estimates of the relative population of CVI to CV ions and ratio of line intensity emitted from them for two representative formulations of dielectronic recombination are presented.     

Opacity effect on extreme ultraviolet radiation from laser-produced tin plasmas

Opacity effects on extreme ultraviolet (EUV) emission from laser-produced tin (Sn) plasma have been experimentally investigated. An absorption spectrum of a uniform Sn plasma generated by thermal x rays has been measured in the EUV range (9-19 nm wavelength) for the first time. Experimental results indicate that control of the optical depth of the laser-produced Sn plasma is essential for obtaining high conversion to 13.5 nm-wavelength EUV radiation; 1.8% of the conversion efficiency was attained with the use of 2.2 ns laser pulses.     

Gd靶激光等离子体6.7nm光源的实验研究

本文对Gd靶激光等离子体极紫外光源进行了实验研究, 在 6.7 nm附近获得了较强的辐射, 并研究了6.7 nm 附近光辐射随打靶激光功率密度变化的规律以及收集角度对极紫外辐射的影响. 同时, 对平面Gd靶激光等离子光源的离子碎屑角分布进行了测量, 发现从靶面的法线到沿着靶面平行方向上Gd离子数量依次减少. 进一步研究结果表明采用0.9 T外加磁场的条件下可取得较好的Gd 离子碎屑阻挡效果.     

类钠铜离子软X射线激光三体复合泵浦机制的研究

 详细研究了类钠铜离子激光等离子体中的各种复合过程，并从理论上描述了类钠铜离子软X射线激光的低温三体复合泵浦机制。     

CO2激光锡等离子体极端紫外及可见光光谱

利用CO2激光烧蚀锡靶产生等离子体,当入射到靶面的单个脉冲能量为400mJ,半峰全宽(FWHM)为75ns时,使用光谱仪和增强型电荷耦合器件(ICCD)采集了等离子体的时间分辨光谱。在局域热平衡假设下,利用谱线的斯塔克展宽和五条Sn II谱线的相对强度计算并得到了等离子体电子密度、电子温度和辐射谱线强度随时间的变化规律;利用掠入射极端紫外平场光栅光谱仪,结合X射线CCD同时探测了光源在6.5～16.8nm波段的时间积分极端紫外辐射光谱。实验结果表明:激光点燃等离子体早期的100ns内有很强的连续谱,此后才能分辨出明显的原子和离子线状谱。在延时0.1～2.0μs的时间区间内,等离子体中的电子温度和密度分别在2.3～0.5eV和7.6×1017～1.2×1016 cm-3范围内,均随时间经历了快速下降,然后再较缓慢下降的过程。激光锡等离子体极端紫外不可分辨辐射跃迁光谱峰值中心位于13.5nm,FWHM为1.1nm。     

Pump–probe studies of EUV and X-ray emission dynamics of laser-irradiated noble gas droplets

The interaction of high intensity 100-ps laser pulses with micron-sized noble gas (argon and krypton) droplets is experimentally investigated via a series of pump–probe experiments monitoring the delay-dependent X-ray and extreme ultraviolet (EUV) emission, and by imaging frequency-doubled probe light scattered from the interaction region. An understanding of the time scales for this interaction is important for optimization of EUV sources for next-generation lithography that utilizes laser-produced plasmas (LPP). Depending on the spectral region of interest, the type of emission, and the droplet characteristics, the effective emission lifetime was found to extend from a few hundred picoseconds to as long as several nanoseconds, in agreement with the expected plasma expansion, EUV excitation, and recombination emission time scales. Received: 22 August 2002 / Accepted: 8 February 2003 / Published online: 28 May 2003 RID="*" ID="*"Corresponding author. Fax: +1-301/3149-363, E-mail: riq@wam.umd.edu     

X-ray spectrometry of laser-produced aluminum plasmas

X-ray lines and continuum emission from a laser-produced aluminum plasma have been studied. The electron temperature variations during the laser pulse (30 ns) were deduced from time-dependent measurements of intensities of resonance lines (2.5 ns time-resolution). Comparison is made with electron temperature values deduced from ion emission measurements.     

高分辨椭圆弯晶谱仪在激光等离子体实验中的应用

 描述了用于激光等离子体X射线光谱研究的椭圆弯曲晶体谱仪系统。在“神光Ⅱ”第九路激光上对该谱仪进行标定实验,利用CCD相机成功地获得了激光等离子体铝和钛离子的K壳层和金离子M壳层谱;通过研究和辨认谱线,得到了X射线光谱,同时还给出了实验测定的谱仪分辨率。椭圆弯曲晶体谱仪除有高的收集光子效率外,还有更好的谱分辨和空间分辨率。分析了椭圆弯曲晶体谱仪在前沿科学技术和高技术实验中的应用。     

Scaling of betatron X-ray radiation

Energetic electron beams accelerated in a laser-produced plasma wakefield cavity can generate collimated beams of X-ray radiation. The oscillation of the electrons in the plasma cavity produces synchrotron-like emission, called betatron radiation. On the basis of state of the art experiments, we discuss the potentiality of this source in terms of spectral brigthness and flux. These characteristics are compared to existing and planned X-ray sources in both laser and accelerator communities.     

Intense xenon capillary discharge extreme-ultraviolet source in the 10-16-nm-wavelength region

We have observed intense extreme-ultraviolet emission, within the 10-16-nm-wavelength range, emitted by a xenon capillary discharge plasma. Within a 0.3-nm bandwidth centered at 13.5 nm the axial emission intensity was comparable with that from the brightest laser-produced plasma sources, and a similar intensity was measured at approximately 11.3 nm. This source could thus be suitable for extreme-ultraviolet imaging applications, such as extreme-ultraviolet lithography.