软X射线激光探针诊断高$lt;i$gt;Z$lt;/i$gt;材料等离子体

激光辐照靶产生的等离子体电子密度的诊断对于惯性约束聚变、高能量密度物理等相关领域的研究具有重要意义,特别是高Z材料等离子体临界面附近的电子密度分布信息的测量. 利用软X射线激光作为探针是诊断等离子体电子密度分布的一种重要方法,但在诊断激光辐照高Z材料产生的等离子体研究中,遇到了高Z材料等离子体自发辐射过大的问题,难以开展. 为此,针对软X射线激光的特点,发展了多种具体的实验技术. 通过综合利用这些技术,大大的抑制了待测等离子体自发辐射对信号的影响,使得软X射线激光探针诊断高Z材料等离子体成为可能. 作为典型例子,实验诊断了激光辐照金平面靶的等离子体,获得了清晰的实验图像,表明相关的技术是有效和可行的. 关键词： 等离子体诊断 激光探针技术 软X射线激光 Z材料等离子体')" href="#">高Z材料等离子体     

Transmission grating spectrograph with on-line recording of XUV soft X-ray spectra from laser produced plasmas

The setting up and on-line operation of a transmission grating spectrograph in the XUV soft X-ray region is described. The detector was a microchannel plate–image intensifier combination, and the output of the image intensifier was coupled to a CCD camera–frame grabber system through an imaging lens. The spectrograph could be operated in the 5–20 Å range with 0.6 Å spectral resolution and in the 5–50 Å range with 1 Å resolution, respectively. The high sensitivity of the detector enables single shot operation, which is useful for several laser plasma interaction studies.     

均匀线状激光等离子体X光单色源和软X光胶片响应特性的标定

利用均匀线聚焦激光产生的等离子体和软X针孔透射光栅谱仪获得了均匀的线状软X光单色光源.在这一光源基础上,利用加阶梯膜的新方法首次标定了国产无保护层5F软X光胶片在软X光波段的响应特性.     

Mitigation of energetic ion debris from Gd plasma using dual laser pulses and the combined effect with ambient gas

For the next-generation beyond extreme ultraviolet lithography(EUVL) sources, gadolinium(Gd) plasma with emission wavelength at 6.7 nm seems to be the leading candidate. Similar to the Sn target 13.5 nm light source, ion debris mitigation is one of the most important tasks in the laser-produced Gd plasma EUV source development. In this paper,a dual-laser-pulse scheme, which uses a low energy pulse to produce a pre-plasma and a main pulse after a time delay to shoot the pre-plasma, is employed to mitigate the energetic ion generation from the source. Optimal conditions(such as pre-pulse energy and wavelength, and the time delay between the pre-pulse and the main pulse for mitigating the ion energy) are experimentally obtained, and with the optimal conditions, the peak of the ion energy is found to be reduced to1/18 of that of a single laser pulse case. Moreover, the combined effect by applying ambient gas to the dual-pulse scheme for ion debris mitigation is demonstrated, and the result shows that the yield of Gd ions is further reduced to around 1/9 of the value for the case with dual laser pulses.     

Optimization of neon soft X-rays emission from 200 J fast miniature dense plasma focus device: A potential source for soft X-ray lithography

The neon soft X-ray (SXR) emission characteristics of a Fast Miniature Plasma Focus (FMPF-3) device have been investigated. The FMPF-3 device used for our experiment is of sub-kilojoule energy capacity, which is an order of magnitude lesser than the other well established plasma focus devices. The influence of different geometrical parameters of the anode and the pressure of the filling gas on the SXR emission was investigated to optimize the neon SXR yield and thereby make it a potential source for X-ray lithography. The SXR signal, solely from the desired, characteristic spectral range (900–1600) eV was selectively extracted and acquired using appropriate X-ray absorption filters on diode X-ray spectrometer. It was found that the neon SXR emission from 17 mm long cylindrical anode, which produced best neutron yields, was rather poor, in a very narrow pressure range and that too at low operating pressure. With decrease in the length of cylindrical anode, the optimum operating pressure shifts to higher pressure side, the working pressure range widens and the SXR yield also increases until the anode length is reduced to 12 mm, after which, the SXR yield and working pressure range start to degrade. The highest neon SXR yield of 1.1 J/shot, corresponding to a wall plug efficiency of 0.57%, was obtained for 12 mm long cylindrical anode. The tapered anodes with different length were also designed and tested, but they did not show any significant improvement in neon SXR yield.     

Investigations on laser plasma soft X-ray sources generated with low energy laser systems

Spectra of laser-induced plasmas at low laser energies and intensities (around 100 mJ and 10¹⁰ W cm^–2 respectively) have been recorded in the spectral range of 20 to 100 nm for different target materials, laser intensities at the target and laser wavelengths. For heavy target materials, a broadband spectrum with a spectral maximum typically around 30 nm is obtained. This broadband radiation source is well suited for photoionization processes and the generation of short wavelength inner-shell photoionization lasers. For the cadmium-photoionization laser, the influence of different soft X-ray spectra on the laser energy has been investigated. The potential of laser plasma soft X-ray sources for scientific and technical applications is briefly reviewed.Dedicated to Prof. Dr. Herbert Welling on the occasion of his 60th birthday     

半圆柱壳槽靶的激光等离子体软X射线光谱发射特点的研究

通常对一种半圆柱壳槽靶与平面靶激光等离子体软X射线光谱空间分布特点和流体动力学行为的比较,证实这种槽形靶可以有效地提高槽区内等离子体温度,从而增强该区域内的软X＇射线光谱发射.     

空间微小碎片超高速撞击诱发的等离子体特性研究

空间微小碎片超高速撞击航天器表面可产生稠密的等离子体,随着等离子体的扩散可导致静电放电及电磁干扰脉冲的发生,近而威胁航天器在轨安全.本文利用等离子体驱动微小碎片加速器研究了质量为10 5g的空间碎片撞击产生的等离子体基本特性,给出了等离子体总电荷与微小碎片速度之间的关系,获得了等离子体扩散速度参数及等离子体电子密度随时间和空间的演化关系,研究结果对于揭示空间微小碎片撞击诱发放电和电磁干扰脉冲形成的机理具有重要意义.     

Characterization of compact bright soft X-ray source based on picosecond laser plasma

Radiation emission of silicon and aluminum plasmas produced by 40-ps laser pulses with peak intensity above 10¹⁴ W/cm² was studied. High-resolution soft X-rayspectra of H-like and He-like ions were analyzed to determine plasma parameters. We compared the line shape of resonance transitions and their intensity ratios to corresponding dielectronic satellites and the intensities of the intercombination lines of He-like ions with the results of model calculations. Such comparisons gave average values of the electron number density N_e=(1-1.9)×10²¹ cm^-3 and the electron temperature T_e=460–560 eV for Si plasmas and about 560 eV for Al plasmas produced by the first and the second laser harmonics. The plasma size is about 100 μm. According to our estimations, more than 10¹² photons were produced within the resonance line spectral width and in the solid angle 2π during the total decay period. PACS 41.50.+h; 52.25.Os; 52.50.Jm     

亚密度冷等离子体的低功率激光吸收特性分析

当电子密度远低于入射小功率激光所对应的临界密度时,冷等离子体对激光的吸收特性与高密度热等离子体将有很大的差别。在亚密度冷等离子体中,电子与中性粒子间的碰撞将占主导地位,对应的频率远大于电子-离子碰撞频率,这使得碰撞吸收本质发生了变化。亚密度等离子体的电子密度和碰撞频率均较小,它在单位长度传输路径内对常用的工作在可见光、红外波段内的小功率激光的碰撞吸收可以忽略不计。但是对于非正常吸收机制的影响尚需深入研究。     

用于等离子体诊断的ps激光探针

 ps激光探针作为激光等离子体诊断的探针光源，它是通过两次倍频和两次受激喇曼散射，将波长为1 054nm、脉宽约为1ns激光转换成波长为308nm、脉宽小于30ps的紫外光。研究结果表明：探针光系统输出能量大于1mJ，脉宽小于30ps，均匀性较好，运行成功率大于90%，满足了激光等离子体诊断的要求。     

电磁驱动超高速机械快门性能分析

高温高密度等离子体辐射源产生脉冲X射线的同时还产生等离子体碎片,飞散速度分布在0.1~10km/s。研制电磁驱动超高速机械快门,有效通光孔径为40mm×50mm,利用45mm×60mm×100μm的铝膜作为快门叶片,在放电电压20kV、驱动电流80kA、放电周期18μs条件下,获得的快门关门时间小于180μs。将快门放置在距离等离子体X射线源2m处,X射线通过后在180μs时间内关闭光学通道,以阻挡高温高密度等离子体产生的碎片,保护X射线精密探测系统和样品,同时实现等离子体参数的精密测量。     

电磁驱动超高速机械快门性能分析

高温高密度等离子体辐射源产生脉冲X射线的同时还产生等离子体碎片,飞散速度分布在0.1~10 km/s。研制电磁驱动超高速机械快门,有效通光孔径为40 mm50 mm,利用45 mm60 mm100 m的铝膜作为快门叶片,在放电电压20 kV、驱动电流80 kA、放电周期18 s条件下,获得的快门关门时间小于180 s。将快门放置在距离等离子体X射线源2 m处,X射线通过后在180 s时间内关闭光学通道,以阻挡高温高密度等离子体产生的碎片,保护X射线精密探测系统和样品,同时实现等离子体参数的精密测量。     

脉冲激光辐照液滴锡靶等离子体极紫外辐射的实验研究

采用波长13.5 nm的极紫外光作为曝光光源的极紫外光刻技术是最有潜力的下一代光刻技术之一, 它是半导体制造实现10 nm及以下节点的关键技术. 获得极紫外辐射的方法中, 激光等离子体光源凭借转换效率高、收集角度大、碎屑产量低等优点而被认为是最有前途的极紫外光源. 本文开展了脉冲TEA-CO₂激光和Nd:YAG激光辐照液滴锡靶产生极紫外辐射的实验, 对极紫外辐射的谱线结构以及辐射的时空分布特性进行了研究.实验发现: 与TEA-CO₂激光相比, 较高功率密度的Nd:YAG激光激发的极紫外辐射谱存在明显的蓝移; 并且激光等离子体光源可以认为是点状光源, 其极紫外辐射强度随空间角度变化近似满足Lambertian分布.     

微小碎片加速器同轴枪内等离子体轴向速度研究

等离子体驱动微小碎片加速器是地面模拟空间微小碎片超高速撞击实验的装置, 决定其加速效果的是加速器同轴枪内等离子体轴向速度. 采用发射光谱法研究等离子体轴向速度随放电电压和工作气体压强的变化关系. 实验结果揭示:轴向速度随着放电电压的增大线性增加,随工作气压的增大而缓慢减小, 与数值模拟结果符合.为进一步提高等离子体轴向速度,优化加速器提供了可靠依据.     

长脉冲keV X射线源的辐射特征

 利用神光Ⅱ第九路2 ns长脉冲激光束作用厚钛固体靶,研究了产生的keV X射线源的辐射区域和总辐射功率的时间行为。结果表明：在长脉冲激光作用厚固体靶时,硬X射线线辐射功率的时间行为以及辐射体积的时间行为与激光脉冲波形一致;长脉冲时,等离子体2维膨胀效应非常显著,keV X射线线辐射的径向辐射区域在激光焦斑尺寸附近达到饱和,导致X射线线辐射功率出现饱和,且keV X射线线辐射的辐射体积正比于焦斑尺寸的3次方。从理论和实验角度研究了在同样入射激光能量下,辐射功率随激光焦斑尺寸的变化关系,发现keV X射线线辐射的饱和辐射功率正比于焦斑尺寸的5/3次方,理论结果与实验结果一致。并讨论了相同基频输出激光能量下,keV X射线辐射总功率随激光波长的变化关系,发现即使考虑了倍频效率的影响,短波长激光仍然有利于keV X射线的发射。     

A pulse-train laser driven XUV source for picosecond pump–probe experiments in the water window

We describe the development of a table top soft X-ray source based on a laser produced plasma. The plasma is produced by a Nd:YLF pulse-train laser which delivers pulse trains of up to 400 pulses each of about 25 ps duration. Number and energy of the micropulses are fully computer controlled adjustable for an optimum interaction with a rotating solid target. Spectral, spatial and temporal characteristics of the X-ray emission from Mylar and copper targets have been studied. A calibrated back-illuminated CCD camera together with a slit grating spectrograph were utilized for the measurement of the absolute soft X-ray photon fluxes. The temporal measurements were performed using a streak camera while the plasma size was measured with a zone plate. An application of the system in a X-ray absorption experiment is shown. The advantages of the system in view of possible optical pump and soft X-ray probe experiments will be discussed.     

激光等离子体相互作用的数值模拟

 基于激光等离子体相互作用的复杂物理过程的数学模型，采用PIC方法分别研究了P极化和S极化非均匀短脉冲强激光入射均匀分布的稠密等离子体时引起的空泡、成丝等物理现象。模拟了激光脉冲在真空中的3维传播形貌。由3维密度分布图发现：激光产生的巨大的有质动力向两侧推动粒子，形成等离子体密度通道；当激光脉冲入射等离子体区域后，纵向加速的电子速度峰值出现在电流峰值处。     

激光等离子体推进技术研究新进展

随着激光技术的发展,激光等离子体推进技术越来越来呈现出其独特的优势,现在已成为当前科学研究和推进领域的研究热点之一.文章对激光等离子体推进技术的应用以及目前的研究进展进行了总结.     

基于脉冲激光的空间碎片移除技术:综述与展望

近年来,近地轨道的空间碎片问题对航天应用的威胁日益严峻。通过主动移除技术手段减少在轨空间碎片的数量,从而保障空间资源的可持续开发和航天器的安全运行,已成为相关领域研究的热点。溯源了空间碎片问题的产生及沿革,分析基于不同技术途径的主动移除方案的特点。重点研究了脉冲激光主动移除空间碎片的关键技术与科学问题,总结了现阶段的技术发展情况,并对未来天基激光移除空间碎片的发展方向给出了建议。