Non-Linear Excitation and Decay of Low-Energy Nuclear Isomers Produced under Femtosecond Laser–Plasma Interaction

The properties of internal electronic conversion of nucleus excited in hot dense laser plasma are considered. The important role of dynamics of plasma charge state in residual gas is shown. We are also considering the role of multi-quanta photoexcitation of low-energy nuclear levels in this plasma. This revised version was published online in August 2006 with corrections to the Cover Date.     

飞秒和纳秒激光脉冲作用下等离子体X射线辐射特性

对飞秒和纳秒激光作用下的Ａｌ和Ｃｕ等离子体的Ｘ射线辐射进行了测量、分析和比较．实验结果表明在飞秒激光脉冲下等离子体Ｘ射线峰值向短波方向移动．同时Ａｌ等离子体的的电离阶数和温度在飞秒下比纳秒高．     

冷冻靶激光等离子体软X射线源

报道了以固态ＣＯ２作为靶材的一种新型激光等离子体软Ｘ射线源，与常规金属靶激光等离子体软Ｘ射线源相比，它是一种低污染的光源，深入研究正在进行中。     

激光等离子体光源软X射线反射率计

介绍了所研制的激光等离子体光源软X射线反射率计,该反射率计由激光等离子体光源、掠入射光栅单色仪、样品室、真空系统、样品台、光电探测系统和计算机控制系统组成,工作波段8～30 nm,测量样品的最大尺寸为130 mm×120 mm×120 mm(长×宽×高),可以利用这台反射率计对软X射线波段光栅、滤光片和多层膜反射镜等光学元件进行测量和评估。为检验反射率计的性能指标,利用该反射率计对本室研制的软X射线多层膜反射镜的反射率进行了测量,测量结果与理论计算结果符合较好,反射率测量重复性为±0.6%。     

Fluorescence Studies of Melanin by Stepwise Two-Photon Femtosecond Laser Excitation

Fluorescence of synthetic melanin in the solvents H₂O, KOH, ethylene glycol monomethyl ether, and dimethyl sulfoxide has been excited by two-photon absorption at 800 nm, using 120-fs pulses with photon flux densities of 10²⁷ cm^–2.S^–1. Compared to the one-photon (400-nm)-induced fluorescence of melanin, the overall spectral shape is red-shifted and shows a strong environment sensitivity. The decay of the two-photon-induced fluorescence (TPF) of melanin is three-exponential, with a shortest main component of about 200 ps. The results of the TPF studies in line with the unique light absorption property of melanin of a monotonously decreasing absorption spectrum between the near UV-region and the near infrared region indicate that the TPF is realized via stepwise absorption of two 800-nm photons. In comparison to the simultaneous absorption of two photons, the stepwise process needs lower photon flux densities to get a sufficient population of the fluorescent level. This stepwise process offers new possibilities of selective excitation of melanin in skin tissue in a spectral region where there is no overlap with any absorption of another fluorescent tissue component. The first results with different samples of excised human skin tissue (healthy, nevus cell nevi, malignant melanoma) suggest that fluorescence excited in this way yields information on malignant transformation.     

等离子体X射线激光介质均匀性测量

通过合理而有效地按排多种探测仪器，观察到等离子体Ｘ射线激光介质的空间非均匀现象。在保证入射激光经最佳组合透镜后焦线均匀性前提下，由实验显示等离子体介质的空间不均匀性主要来自靶材质量和调焦精度。此外，入射激光脉宽的大小变化将会引起等离子体整个辐射空间和时间范围的明显变化。     

用光线矩阵元描述X射线激光输出特性

采用矩阵光学方法，研究了串接多靶，弯曲靶加反射镜“双程放大”Ｘ射线激光输出特性，给出了发散角普遍公式，分析了电子密度梯度分布，反射镜角失调对Ｘ射线激光输出场分布的影响，所得结果与已有实验符合较好，最后，对如何从靶，Ｘ光学元件空间排布来实现衍射极限的输出发散角提出了新的设想，作了半定量的探讨。     

Effect of Discharge Plasma Potential on Diffusion Plasma Parameters Controlled by a Mesh Grid in a Double Plasma Device

The plasma region under investigation is separated from the discharge region by a mesh grid. Plasma potential and electron number densities and electron temperatures under bi‐Maxwellian approximation for electron distribution function of the multi‐dipole argon plasma are measured. The cold electrons in the diffusion region are produced by local ionization. The hot electrons are the ionizing electrons behaving as Maxwellian. The electron trapping process in the discharge region is produced by potential well due to positive plasma potential with respect to the anode and by a repulsive grid. The dependence of ratios of the density of the hot to the cold electrons N_E (=N_eh/N_ec) and hot to cold electron temperature T(=T_eh/T_ec) in the diffusion region on the depth of the potential well has been investigated. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

激光等离子体软X射线接近式光刻术初步研究

描述了用高功率脉冲激光打靶产生的等离子体作为软Ｘ射线源而进行的接近式软Ｘ射线光刻研究，采用负性辐射线光刻胶聚氯甲基苯乙烯，得到了一些新的实验结果。     

短密度梯度尺度等离子体中的软X射线激光

通过数值求解等离子体流体力学方程组，研究了短脉冲激光打靶结束后形成的短密度梯度尺度等离子体的冷降温过程，讨论了热传导，膨胀作功，辐射损失三种冷却机制对降温过程的贡献，并用解流体力学方程组得到的等离子参数计算ＭｇＸＩ等离子体中波长小于２０ｎｍ的所有可能跃迁的自发辐射放大增益系数，分析了它们与环境条件的关系，指出了在ＭｇＸＩ等离子体中获取水窗附近乃至水窗波段软Ｘ射线激光的可能性。     

Diagnose Parameters of Plasma Induced by Femtosecond Laser Pulse in Quartz and Glasses

Electron plasma induced by a focused femtosecond pulse (130 fs, 800 nm) in quartz, fused silica, K9 glass, and Soda Lime glass was investigated by pump-probe technology. Pump and probe shadow imaging and interferometric fringe imaging have been used to determine plasma density, relaxation time, and electron collision time in the conduction band. In these materials, the electron collision time is about several femtoseconds when the electron density is in the 10¹⁹cm⁻³ range. The electron relaxation processes are different: lifetime is about 170 fs in pure quartz and fused silica, and about 100 ps in K9 and Soda Lime glass. The modified electron band by doped ions is regarded to be responsible for the difference of decay time in these materials.     

Nonlinear Excitation of Tryptophan Emission Enhanced by Silver Nanoparticles

We measured and analyzed the behavior of the fluorescence of tryptophan water solutions with and without silver nanoparticles, excited by one, two and three photon processes. Two different colloids with silver nanoparticles with distinct diameters (0.65 nm and 9 nm) were used in the experiments. Fluorescence quenching was observed with one and two photon excitation. However, upon three-photon excitation, significant fluorescence enhancement was observed in the colloid. In this case excitation of the amino acid is assisted by the nonlinear absorption of infrared light by the silver nanoparticles. In this paper we are proposing a new way to explore metallic nanoparticles to enhance autofluorescence of biomolecules.     

脉冲激光制备类金刚石薄膜及原位激光等离子体发射光谱

用ＹＡＧ脉冲激光轰击真空室内的石墨靶,可以形成包含碳素的激光等离子体,并在硅或石英衬氏上淀积形成某种类型的碳膜。用光学多道分析仪原位测量了激光等离子体的发射光谱,给出反应空间可能存在的反应基团有碳原子、碳离子、碳分子等,用拉曼光谱研究了薄膜的结构,证明所形成的薄膜为类金刚石膜,并得出碳原子和碳离子与薄膜的类金刚石结构有关。制备过程中,氢的参与有利于薄膜中金刚石成分的形成。空间分辨的原位激光等离子体发射光谱表明,在反应空间存在薄膜形成的最佳位置。     

同轴空心阴极氦等离子体的电子激发温度研究

利用同轴空心阴极放电装置,产生氦低温等离子体。通过对等离子体的发射光谱进行测量和计算,研究放电功率以及氦气压强对等离子体的电子激发温度的影响。结果表明:氦低温等离子体的发射光谱主要由连续谱和原子谱线构成,放电功率和压强对谱线的强度具有明显影响。压强的变化不仅影响电子从电场中获得的能量,还会影响电子与原子的碰撞频率,从而导致电子激发温度随着氦气压强的增大,出现先上升后下降的变化趋势。     

脉冲激光烧蚀碲镉汞材料的等离子体发射谱

脉冲激光辐照处于不同背景气压下的Hg0.8Cd0.2Te材料表面,用时间和空间分辨诊断技术探测了激光照射后产生的等离子体发射谱,根据所获得的飞行时间谱测量了等离子体中粒子的出射速度,结果表明粒子速度随着出射距离的增加迅速减小,且背景气压对出射速度有很大的影响,而激光能量对粒子速度的影响不大。另外根据谱线的展宽计算了等离子体中的电子密度,结果表明,电子密度在激光辐照样品后的短时间内迅速减小,且电子密度最大的位置不是出现在靶的表面而是在距表面一定距离处。     

激光选态激发的量子逻辑功能

基于三模激光与三能级分子相互作用时态的布居依赖于激光的位相和振幅,提出利用激光选态激发,实现Ｆｒｅｄｋｉｎ量子逻辑门的功能。     

斜入射泵浦等离子体状态研究

 研究了作用在靶介质上的斜入射泵浦激光,对产生的靶等离子体状态以及激光增益区的影响。研究结果表明,等离子体状态和激光增益区随入射角θ0 (20(变化而变化。当θ0≤20°时这种变化不大。当θ0约30°时等离子体状态和激光增益区有比较明显的变化。当θ0≥40°时, 状态有很大的变化,严重影响激光增益和放大。     

飞秒强激光与欠稠密等离子体相互作用中的二次谐波辐射

对超短超强激光脉冲 (45fs,6× 10 17W /cm2 )与光致电离氦气形成的欠稠密等离子体相互作用中的二次谐波辐射进行了实验研究。测量了多种打靶强度的飞秒激光脉冲与不同气体密度氦气相互作用的二次谐波光谱 ,得到在欠稠密等离子体中二次谐波辐射与打靶激光能量的关系 ,分析了产生二次谐波辐射产生的物理机制 ,在考虑了强短脉冲激光电离气体产生的等离子体径向电子密度梯度因素 ,基于非线性作用过程的理论预期曲线与实验结果较好地吻合     

Nuclear Excitation by Electron Transition and Gamma-Ray Laser

This paper studies nuclear excitation by electron transition (NEET) and is potential application in developing gamma-ray laser.A quantum mechanics formula to calculate NEET probabilities was presented with emphasis on the calculations of the transition matrix elements and discussions of the transition selection rules.The NEET probabilities for a number of nuclides were calculated.The upper limit of NEET probability is evaluated to be about 10^－5.The possibility for applying the technique of NEET in the development of gamma laser was investigated.