超短超强激光脉冲辐照超薄碳膜电离状态研究

为了进一步理解极端条件下物质的电离特性, 特别是超短超强激光脉冲辐照超薄靶时等离子体的形成与分布, 本文以超薄碳膜为例, 细致研究了超短超强激光脉冲辐照下原子的离化过程. 分析和比较了强激光场直接作用电离和靶内静电场电离等两种场致电离形式, 在碰撞电离可以忽略的情况下, 发现更多的电离份额是来自靶内静电场的电离方式. 研究了激光脉冲强度对电离的影响, 发现激光脉冲强度越强, 电离速度越快, 产生的高价态离子所占比例也越高.当激光强度为1×10²⁰ W/cm²时, 尽管该强度高于电离生成C⁺⁶所需要的激光强度阈值, 但该激光脉冲并不能将整个靶电离成C⁺⁶离子, 对此本文进行了详细的分析. 在研究激光脉冲宽度的影响时, 发现激光脉宽越小, 电离速度越快, 但越小的激光脉冲电离获得的高价态离子越少.     

纳秒强激光场中甲醇光电离产生高价离子的研究

利用25ns脉冲Nd YAG 532nm的激光，在1011 W·cm-2的光场强度下，利用飞 行时间质谱对He, N2, Ar载气条件下甲醇的激光电离过程进行了研究.发现当利用氩作为 载气时，除观察到一般多光子电离所产生的离子和碎片离子外，还观察到很强的Cq+(q=2-4)和Oq+(q=2—4)高价离子.这些离子都有很高的平动能，通 过改变载 气种类和压力以及使用不同延迟条件的脉冲电场的实验，可以认为这些高价离子来源于含甲 醇团簇的库仑爆炸过程.这些实验结果为发展库仑爆炸理论研究提供新思路. 关键词： 甲醇 纳秒激光 高价离子 库仑爆炸     

Multiphoton double ionization of Ar in intense extreme ultraviolet laser fields studied by shot-by-shot photoelectron spectroscopy

Photoelectron spectroscopy has been performed to study the multiphoton double ionization of Ar in an intense extreme ultraviolet laser field (hν ～ 21 eV, ～ 5 TW/cm2), by using a free electron laser (FEL). Three distinct peaks identified in the observed photoelectron spectra clearly show that the double ionization proceeds sequentially via the formation of Ar(+): Ar+hν→Ar (+) + e? and Ar2(+) + 2hν→Ar(+) + e?. Shot-by-shot recording of the photoelectron spectra allows simultaneous monitoring of FEL spectrum and the multiphoton process for each FEL pulse, revealing that the two-photon ionization from Ar(+) is significantly enhanced by intermediate resonances in Ar(+).     

Collimated multi-MeV ion beams from high-intensity laser interactions with underdense plasma

A beam of multi-MeV helium ions has been observed from the interaction of a short-pulse high-intensity laser pulse with underdense helium plasma. The ion beam was found to have a maximum energy for He2+ of (40(+3)(-8)) MeV and was directional along the laser propagation path, with the highest energy ions being collimated to a cone of less than 10 degrees. 2D particle-in-cell simulations show that the ions are accelerated by a sheath electric field that is produced at the back of the gas target. This electric field is generated by transfer of laser energy to a hot electron beam, which exits the target generating large space-charge fields normal to its boundary.     

Charge Composition of Ions in a Cluster Plasma Formed under the Action of a High-Power Laser Pulse

A model describing the ionization of atoms and ions in a cluster under irradiation by a short laser pulse has been constructed. It is shown that the electron-impact ionization weakly affects the final charge composition, and the main mechanism of ion formation in the cluster is the over-barrier ionization by an electric field. The electric field acting on atoms and ions is the result of combined action of the external laser field and the intrinsic electric field of the cluster. The key parameters of the cluster beam and the laser pulse, which determine the properties of the charge composition of the cluster plasma, have been established.     

Comparison study of atomic and molecular single ionization in the multiphoton ionization regime

In this Letter, we report, for the first time in the multiphoton ionization regime, a comparison study of single-electron ionization of diatomic molecules versus rare gas atoms with virtually the same ionization potentials. In comparing N2+ to Ar+, a higher ion signal is seen in N2+ compared to Ar+ for linear polarization but the difference vanishes in circularly polarized light. In comparing O2+ to Xe+, we observe a suppression in O2+ compared to Xe+ for both linear and circular polarization but this suppression exhibits an intensity dependence; i.e., there is little suppression for O2+ at the lowest intensity range, but the suppression becomes increasingly stronger as the laser intensity increases. The multielectron screening model is used to discuss possible mechanisms of this intensity dependent suppression in O2+ in the multiphoton ionization regime.     

Cluster-assisted generation of multicharged ions in nanosecond laser ionization of carbon bisulfide clusters at 1064nm

The photoionization of seeded carbon bisulfide molecular beam by a 1064\,nm nanosecond Nd-YAG laser with intensities varying from $0.8\times10^{11}$ to $5.6\times10^{11}$\,W/cm$^{2}$ have been studied by time-of-flight mass spectrometry. Multiply charged ions of S$^{q + }$ ($q$ = 2--6) and C$^{q +}$ ($q$ = 2--4) with kinetic energy of hundreds of electron volts have been observed, and there are strong experimental evidences indicating that those multicharged ions originate from the ionization of CS$_{2}$ neat clusters in the beam. An electron recolliding ionization model is proposed to explain the appearance of those multiply charged atomic ions under such low laser intensities.     

Evidence for rescattering in intense, femtosecond laser interactions with a negative ion

It is now well established that energetic electron emission, nonsequential ionization, and high harmonic generation, produced during the interaction of intense, femtosecond laser pulses with atoms (and atomic positive ions), can be explained by invoking rescattering of the active electron in the laser field, the so-called rescattering mechanism. In contrast for negative ions, the role of rescattering has not been established experimentally. By irradiating F- ions with ultrashort laser pulses, F+ ion yields as a function of intensity for both linearly and circularly polarized light have been measured. We find that, at intensities well below saturation for F+ production by sequential ionization, there is a small but significant enhancement in the yield for the case of linearly polarized light, providing the first clear experimental evidence for the existence of the rescattering mechanism in negative ions.     

产生惰性气体高价离子的新方法

此文介绍了一种产生惰性气体高价离子的新方法。在飞行时间质谱仪（ＴＯＦ－ＭＳ）上，把聚焦后的３０８ｎｍ激光掠射到不锈钢栅网上，产生超短脉冲的电子束，利用这种电子束来轰击惰性气体（Ｈｅ，Ｎｅ，Ａｒ，Ｋｒ，Ｘｅ），产生高价离子，并给出了这些离子的飞行时间质谱。这些高价离子可能是电子逐次电离气体原子产生的。这种方法可作为飞行时间质谱的一种理想的“软电离”的“点”离子源     

1-萘酚团簇的紫外光电离质谱研究

用飞行时间质谱仪和超声速脉冲分子束技术研究了紫外激光对1-萘酚(1HN)团簇的电离质谱.观测到(1HN)_n~+系列的团簇离子,且离子强度随团簇尺寸的增大而减小.电离激光的强度(在5μJ/pulse～100μJ/pulse范围内)对团簇离子强度的相对分布影响较小,说明软电离为产生团簇离子的主要过程,团簇离子的强度分布反映出电离前中性团簇的分布特征.增大电离区的进样气压可以产生更大尺寸的团簇离子,同时在(1HN)_n~+后面观测到新系列的团簇离子.这些新生离子与(H_2O)_m有关,考虑到1-萘酚团簇可以通过OH形成H键,推测该新生团簇离子通过团簇内的反应而产生.     

基于HIRFL-CSR的高速高电荷态重离子与原子碰撞X射线谱学实验设计与研究

依据非相对论偶极近似、相对论程函近似、ECPSSR理论及平面波玻恩近似方法,计算了30～500 MeV/u的Ar18+、Kr36+和Xe54+离子与Ar、Kr和Xe原子碰撞过程中辐射电子俘获、非辐射电子俘获及内壳电离截面.在此基础上,结合光子探测器的能量分辨以及炮弹离子跃迁谱线的多普勒效应等因素,针对HIRFL-CSR...     

氩团簇高信噪比13—23nm软x射线辐射谱实验观察

用150fs的掺钛蓝宝石激光系统, 在功率密度约为5×10¹⁵ W/cm²时 激励氩(Ar)团簇，利用具有空间分辨能力的平场光栅谱仪观察到13—23nm波段Ar的软x射线谱，并观察到Ar的11阶离子谱线.在较宽的激光脉宽和较低的激光功率密度情况下，通过激励Ar团簇，获得 了Ar的高阶电离度的实验结果，且谱线的信噪比明显好于光场感应电离的情况，说明团簇的 形成大幅度地提高了激光能量的吸收效率. 关键词： Ar团簇 超短强激光 软x射线辐射     

Ar辅助确定Al等离子体电子温度

用Ar气作保护气时 ,Nd :YAG脉冲激光烧蚀Al靶 ,将诱发Ar气电离 ,并产生丰富的Ar离子谱线辐射。文章根据Ar离子谱线辐射信息 ,分析了ArⅡ 385 0 5 7,ArⅡ 386 85 3,ArⅡ 4 0 4 2 91 ,ArⅡ 4 0 7 2 0 1nm等 4条谱线的时间分辨行为 ,计算了Al等离子体的电子温度。结果发现 :Al等离子体的电子温度约 1 5 0 0 0～2 2 0 0 0K ,随延迟时间的增加 ,电子温度单调衰减     

激光与固体靶面烧蚀等离子体的能量耦合计算

 强激光辐照下固体靶表面迅速汽化产生靶蒸气等离子体,激光穿过等离子体区到达固体靶表面的过程就是激光束与等离子体的能量耦合与交换过程。采用具有五阶精度的WENO差分格式和简易等离子体状态方程模型对激光与等离子体相互作用的复杂物理过程进行了数值计算,分析了激光束能量在等离子体区中的吸收、屏蔽效应等动态耦合规律以及激光支持等离子体前驱冲击波传播。数值模拟结果表明：激光能量是支持靶面等离子体运动的唯一原因,能量屏蔽效应对激光与等离子体能量耦合有很大影响,通过控制激光脉冲宽度,可以合理调节屏蔽效应的影响。     

Ionization of atoms by the spatial gradient of the pondermotive potential in a focused laser beam

Ionization of atoms by the spatial gradient of the pondermotive potential in a focused laser beam is investigated. Rydberg ions, formed during the interaction of noble gas atoms with an intense laser pulse, are used to probe the gradient field. Rydberg ion species with higher ionization potentials are produced at locations where the gradient field is largest. The measured Rydberg ion yields differ dramatically from estimates that ignore gradient-field ionization, but are in good agreement with predictions that include the effect.     

纳秒强激光中丙酮团簇增强的多价电离现象

利用脉宽为25 ns的脉冲Nd: YAG 532 nm的激光，在10¹⁰—10¹¹ W/cm²的强度下，用飞行时间质谱对丙酮团簇的激光电离过程进行了研究. 观察到了较强的O^q+(q=2—4)和C^q+(q=1—4)高价离子信号，这些高价离子 C⁴⁺，C³⁺，C²⁺，O⁴⁺，O³⁺，O²⁺的最大概然平动能分别为240 eV，70 eV，30 eV，90 eV，80 eV，40 eV. 高价离子的强度和平动能随激光强度的增大而增大. 我们提出一个多光子电离引发，逆韧致吸收加热-电子碰撞电离模型来解释高价离子的产生. 关键词： 丙酮 团簇 库仑爆炸 高价离子     

Ar中抖动现象观察

本文叙述了利用准分于紫外激光打靶产生的软Ｘ射线激励（ＬＰＸ）所观察到的Ａｒ中抖动（Ｓｈａｋｅ－ｕｐ）现象．对Ａｒ＋３ｐ４４ｐ与下能态跃迁产生的６８条谱线进行了识别，标定，除两条谱线没观察到外，其余所有可能产生的跃迁谱线都已被观察到．     

团簇增强的纳秒激光电离产生Xez+(z≤20)高价离子

利用功率密度为1011—1012W·cm-2的1064nm纳秒激光电离氙原子团簇，在飞行时间质谱中观察到电离态高达+20的高价离子.不同脉冲束位置实验表明，仅当激光作用于分子束的中段时，才能观察到高价离子，且高价离子的强度随束源压力的增加而迅速增强.实验结果表明束中大尺寸团簇的存在与高价离子的形成密切相关.讨论了高价离子产生的可能机理. 关键词： 氙 纳秒激光 高价离子 飞行时间质谱     

X-ray emission for Ar11+ ions impacting on various targets in the collisions near the Bohr velocity

X-ray emission from the collisions of 3 MeV Ar¹¹⁺ ions with V, Fe, Co, Ni, Cu, and Zn is investigated. Both the x-rays of the target atom and projectile are observed simultaneously. The x-ray yield is extracted from the original count. The inner-shell ionization cross section is estimated by the binary encounter approximation model and compared with the experimental result. The remarkable result is that the Ar K-shell x-ray yield is diminished with the target atomic number increasing, which is completely opposite to the theoretical calculation. That is interpreted by the competitive consumption of the energy loss for the ionization of inner-shell electrons between the projectile and target atom.     

Production of highly charged argon ions from a room temperature electron beam ion trap

In this work.highly charged ions have been extracted from the advanced Electron Beam Ion Source (EBIS-A) developed in a scientific cooperation between the Dresden University of Technology and the DREEBIT GmbH Dresden.The charge state distributions of ions extracted from the EBIS-A are measured in and extracted in the leaky mode.3×105 Ar18+ ions per pulse are extracted in the pulse mode.The ion charge state distribution is a function of the ionization time.