空气中YAG激光诱导Cu等离子体空间特性的研究

在空气中利用Nd: YAG脉冲激光诱导金属Cu靶,产生激光等离子体羽,并获得等离子体羽的空间谱;研究了空间谱线结构;分析了不同空间位置处电子温度和电子密度的空间演化规律;并对等离子体光谱的特性和产生机制进行了讨论. 结果表明：谱线结构、谱线强度和等离子体的电子温度及电子密度都与空间位置变化密切相关,特征谱强度最大值出现在距靶面0.75-1.0mm的空间位置处,此处CuⅠ谱线相对强度最强,在1.25 mm空间位置处电子温度比周边的电子温度偏低,但此处电子密度反而升高,这种现象可以由级联效应得到解释。     

利用H_β线的Stark加宽计算激光诱导Cu等离子体的电子密度

在潮湿空气中,用Nd:YAG脉冲激光器产生的1.06 μm激光烧蚀金属Cu靶产生等离子体,并观测了其空间分辨的发射光谱.依据光谱线波长、相对强度等参数估算了沿靶面法线不同位置等离子体的电子温度.在此基础上,由H_β线的Stark加宽、分别用三种方法计算得到等离子体的电子密度.讨论了电子温度和电子密度沿靶面法线的空间分布特征.结果分析表明:利用环境气体的谱线测量复杂元素等离子体电子密度的方法是可行的.在距离靶面1.0 mm的空间位置附近电子温度骤然降低、电子密度具有最大值的现象可以从激光诱导等离子体产生机制的角度得到定性解释.     

离焦量对空气中激光诱导铜等离子体光谱特性的影响

利用Nd: YAG脉冲激光在空气中烧蚀金属Cu靶,获得等离子体光谱;采用改变离焦量的方法,研究了离焦量的变化对谱线结构及谱线强度的影响;分析了离焦量分别为1mm、0mm和-2mm时,沿靶面法线方向不同空间距离处电子温度的演化规律;并对等离子体光谱的特性和产生机制进行了讨论. 结果表明,谱线结构、谱线强度和等离子体的电子温度都与离焦量的变化密切相关,聚焦点在-2mm处CuⅠ谱线相对强度出现峰值,电子温度数值最大;聚焦点在-0.5mm和-1.0mm附近谱线相对强度遽然降低的现象是由于等离子体的屏蔽效应造成的.     

利用Hβ线的Stark加宽计算激光诱导Cu等离子体的电子密度

潮湿空气中,利用Nd:YAG脉冲激光烧蚀Cu靶获得等离子体发射光谱,依据谱线波长和相对强度等信息计算了等离子体的电子温度;在此基础上,分别用三种方法由Hβ线的Stark加宽计算得到电子密度,并对结果进行了比较分析,证实：对于电子密度在1015~1016cm-3范围内的等离子体,用Hβ谱线测量电子密度是可靠的. 讨论了等离子体电子温度和电子密度在垂直于靶面方向的空间分布,并从产生机制的角度解释了等离子体的传播过程.     

真空中脉冲激光烧蚀铝等离子体发射光谱及粒子速度研究

利用Q开关Nd:YAG激光器产生的1.06 μm倍频后532 nm、脉宽10 ns的脉冲激光聚焦在置于真空室中铝靶上,观测激光诱导的铝等离子体发射光谱.采用不同的激光能量,分析了波长范围为350 nm到400 nm的空间、时间分辨发射光谱.在局部热力学平衡(LTE)条件近似下,根据谱线的相对强度,计算得到等离子体电子温度,给出了靶面附近电子温度的空间、时间演化规律;根据谱线半宽,计算等离子体电子密度,并给出了靶面附近电子密度的空间与时间演化规律;在靶面正前方处放置动能探测器,记录粒子飞行时间信号,观测不同激光强度烧蚀铝靶产生等离子体中三种粒子到达探测器的时间,计算得出等离子体中三种观测到的粒子喷射速度.     

空气中激光烧蚀Cu产生等离子体发射光谱的研究

利用Q-开关Nd:YAG激光器产生的1.06 μm、10 ns的脉冲激光聚焦在空气中的Cu靶上,观测了激光诱导的Cu等离子体发射光谱.采用不同的激光能量,分析了波长范围为440 nm到540 nm的空间分辨发射光谱.在局部热力学平衡(LTE)条件近似下,根据谱线的相对强度,得到了等离子体电子温度约在104 K以上,给出了靶面附近电子温度的空间演化规律,并探讨了N(Ⅱ)500.52 nm谱线的谱线强度和半高全宽随激光能量的变化规律.     

Gd靶激光等离子体光源离带辐射及其等离子体演化的研究

利用脉冲宽度为10 ns,输出波长为1 064 nm的Nd∶YAG激光器作用金属Gd以及纳米粒子掺杂的低密度Gd玻璃等两种形式靶所产生等离子体光源的离带辐射进行了研究,发现等离子体所发出的连续辐射是离带辐射的主要成分,光谱分布与温度为5 eV的普朗克曲线相匹配。此外,相对于金属Gd靶而言,采用纳米粒子掺杂的低密度Gd玻璃靶可大幅度降低等离子体光源的离带辐射。利用光谱法,对激光作用纳米粒子掺杂的低密度Gd玻璃靶所形成光源的等离子体羽的电子温度和电子密度进行了时空分辨研究。实验结果表明,在打靶结束125 ns时,距靶面6 mm位置处等离子体的电子温度约为4 eV,电子密度约为1.2×1018 cm-3。同时发现在激光打靶结束后等离子体羽的电子温度和电子密度随延时的变化而呈指数下降,在120～250 ns时间范围内,两者下降较快,之后其幅度下降缓慢。另一方面,当打靶脉冲结束约200 ns时,在距离靶面1～10 mm的空间内等离子体的电子温度及密度均经历先上升后下降的变化过程。在距靶材表面6 mm位置处,电子温度和电子密度均达到最大值,电子温度约为2.6 eV,电子密度为8.5×1017cm-3。     

发射光谱法研究纳秒激光烧蚀硅等离子体特性

利用调Q Nd3+∶YAG激光器三倍频355 nm激光脉冲烧蚀空气环境的硅样品,观测不同脉冲激光能量下产生的等离子体在380～420 nm范围内的时间-空间分辨等离子体发射光谱,观测到在等离子体羽膨胀初期存在N+发射光谱。在局域热力学平衡近似条件下,根据时间-空间分辨等离子体发射光谱计算得到等离子羽体电子温度和电子密度随时间延时存在二次指数衰减变化,等离子体羽体电子温度和电子密度的空间分布近似呈Lorentz分布,发现在确定激光脉冲能量下电子密度空间分布最大值偏离光谱强度最大空间位置并对产生原因进行分析,探讨了等离子体羽参数与激光脉冲能量的关系。     

激光等离子体发射谱展宽机制研究

根据激光诱导Cu等离子体的发射光谱特性,详细地讨论了谱线展宽机制;根据谱线的强度和半高宽度,计算了等离子体的电子温度和密度,给出了电子密度的时间和空间的演化规律。     

激光诱导Ti等离子体光谱的时间演化特性研究

利用Nd:YAG激光器产生的1064 nm、10 ns脉冲激光聚焦在空气中的Ti靶,观测了激光诱导Ti等离子体发射光谱.调节激光能量为45 mJ/pulse,分析了时间范围在0到4000 ns的时间分辨发射光谱和谱线轮廓以及展宽.在局部热力学平衡(LTE)条件下,利用Saha-boltzmann图法拟合电子温度,Saha方程计算电子密度,讨论了等离子体电子温度和电子密度随时间的演化规律.结果表明,在所讨论的时间范围内,谱线的强度在延时250 ns处达到最大,250 ns后随着延迟时间的增加减小,电子密度和电子温度在延时1000 ns内快速衰减,1000 ns后衰减速度变慢.     

低能电子显微术及其应用

低能电子显微术是新发展起来的一种显微探测技术。它的特点是利用低能（１－３０ｅＶ）电子的弹性背散射使表面实空间实时成像，具有高的横向（１５ｎｍ）和纵向（原子级）分辩率，且易与低能电子衍射及其他电子显微术相结合。近年来它已有效地应用于金属和半导体表面的形貌观测、表面相变、吸附、反应及生长过程的研究。     

On the interpretation of the electron anomalous magnetic moment

Guided by a Compton-sized model, we demonstrate that: (a) the magnetic self-energy of the electron, as estimated initially by Rasetti and Fermi, can be directly related to both the sign and the magnitude of the electron anomalous magnetic moment; and (b) the classical expression for the magnetic self-energy of the electron exhibits the same characteristic logarithmic divergence that occurs in QED. This electron model quantitatively reproduces the spin, magnetic moment, and gyromagnetic ratio of the electron, correct to first order in = e² /c. It also relates the quantum-mechanical spin projection angle to the vanishing of the electric quadrupole moment, and it is capable of reproducing point-like scattering behavior.     

The effects of self-fields on the electron trajectory in a two-stream free electron laser with a helical wiggler and an axial guiding magnetic field

A theory for the two-stream free-electron laser(TSFEL) with a helical wiggler and an axial guide magnetic field is developed.In the analysis,the effects of self-fields are taken into account.An analysis of the two-stream steady-state electron trajectories is given by solving the equation of motion.Numerical calculations show that there are seven groups of orbits in the presence of self-fields instead of two groups reported in the absence of self-fields.The stability of the trajectories is studied numerically.     

Relaxation between electrons and surface phonons of a homogeneously photoexcited metal film

The energy relaxation between the hot degenerate electrons of a homogeneously photoexcited metal film and the surface phonons (phonon wave vectors in two dimensions) is considered under Debye approximation. The state of electrons and phonons is described by equilibrium Fermi and Bose functions with different temperatures. Two cases for electron scattering by the metal surface, namely specular and diffuse scattering, are considered.     

北京自由电子激光器电子束截面监测系统

报告了北京自由电子激光器(BFEL)从30MeV直线加速器出口到摇摆磁铁出口束流输运段的束流截面监测系统。该系统由四台遥控气动可伸缩荧光屏探头、光学放大系统、闭路电视摄象系统及视频图象处理系统组成。利用该系统进行模拟实验,其系统空间分辨率约100μm,达到BFEL总体要求。利用该系统可以测量摇摆磁铁入口处及内部电子束和准直激光的截面、位置和畸变,进行束流准直、聚焦和发射度测量。     

Investigation of the effect of electron cyclotron heating on runaway generation in the KSTAR tokamak

Wave enhanced runaway generation is expected to play an important role in the conversion of plasma current into runaway current during major disruptions. The fast electrons created by electron cyclotron heating (ECH) were used to study this issue in KSTAR. It is found that the fast electrons driven by ECH can enhance runaway production in the flat top phase with high loop voltage. The runaway current in disruptions was not enhanced by the ECH produced fast electron population due to the strong magnetic fluctuations which inhibited the generation of runaway electrons. It is found that a complete loss of existing REs during thermal quench has occurred in KSTAR limiter configuration discharges.     

Near threshold photodetachment cross section of negative atomic oxygen ions

A 40-target state close-coupling calculation for the photodetachment cross section of negative atomic oxygen near threshold is carried out with core－valence electron correlation by using the R-matrix method. It was shown that after considering the excitations of two electrons from the 2s shell, the electron affinity of O^- (2s^22p^5{}^2P°) agrees with the experimental result much better than that just considering the excitations of electrons only from the 2p shell as well as only one electron from the 2s shell. Total cross section as well as the main contribution of the ionization channels to the partial cross section are illustrated to show the structure near threshold clearly.     

Holes drilling in gold and silver decahedral nanoparticles by the convergent beam electron diffraction electron beam

The 200?kV focused electron beam in the convergent beam electron diffraction patterns mode in a transmission electron microscope (TEM) with field emission gun is able to drill holes in gold and silver decahedral nanoparticles. However, although they are done under the same circumstances, the holes are shapeless in the silver and faceted in gold nanoparticles. In addition to this, the holes are closed during their high-resolution TEM observation in both materials. To comment their differences, displacement energy considerations are taken into account as function of the sputtering energy in order to modify the displacement cross-section of the processes.     

Commissioning of electron cooling in CSRe

The 400 MeV/u 12C6＋ ion beam was successfully cooled by the intensive electron beam near 1 A in CSRe.The momentum cooling time was estimated near 15 s.The cooling force was measured in the cases of difierent electron beam profiles,and the difierent angles between the ion beam and electron beam.The lifetime of the ion beam in CSRe was over 80 h.The dispersion in the cooling section was confirmed as positive close to zero.The beam sizes before cooling and after cooling were measured by the moving screen.The beam diameter after cooling was about 1 mm.The bunch length was measured with the help of the signals from the beam position monitor.The difiusion was studied in the absence of the electron beam.