Angular distribution and conversion of multi-keV L-shell X-ray sources produced from nanosecond laser irradiated thick-foil targets

An experimental study on the angular distribution and conversion of multi-keV X-ray sources produced from 2 ns-duration 527nm laser irradiated thick-foil targets on Shenguang II laser facility (SG-II) is reported. The angular distributions measured in front of the targets can be fitted with the function of f(theta) = alpha+ (1- alpha)cos(beta) theta (theta is the viewing angle relative to the target normal), where alpha = 0.41 +/- 0.014, beta = 0.77 +/- 0.04 for Ti K-shell X-ray Sources (similar to 4.75 keV for Ti K-shell), and alpha = 0.085 +/- 0.06, beta = 0.59 +/- 0.07 for Ag/Pd/Mo L-shell X-ray Sources (2-2.8 keV for Mo L-shell, 2.8-3.5 keV for Pd L-shell, and 3-3.8 keV for Ag L-shell). The isotropy of the angular-distribution of L-shell emission is worse than that of the K-shell emission at larger viewing angle (>70 degrees), due to its larger optical depth (stronger self-absorption) in the cold plasma side lobe Surrounding the central emission region, and in the central hot plasma region (emission region). There is no observable difference in the angular distributions of the L-shell X-ray emission among Ag, Pd, and Mo. The conversion efficiency of Ag/Pd/Mo L-shell X-ray sources is higher than that of the Ti K-shell X-ray sources, but the gain relative to the K-shell emission is not as high as that by using short pulse lasers. The conversion efficiency of the L-shell X-ray sources decrease, with increasing atomic numbers (or X-ray photon energy), similar to the behavior of the K-shell X-ray Source.

利用皮秒脉冲激光驱动瞬态X射线激光

报道了利用皮秒激光驱动产生瞬态类镍银X射线激光的实验结果．采用一路脉冲宽度为数百皮秒的激光作为预脉冲，配合另一路皮秒激光作为主脉冲联合驱动平面靶，获得了一定强度的类镍银X射线激光输出，输出能量约为5-10nJ．

利用x射线激光干涉诊断等离子体电子密度

x射线激光探针干涉方法是诊断高温高密度激光等离子体电子密度等信息的重要工具．利用神光Ⅱ装置输出激光驱动的类镍-银x射线激光作为探针，成功地进行了马赫-曾德尔干涉法诊断实验，获得了清晰的包含等离子体信息的动态干涉条纹图像，并据此给出了待测C8H8等离子体临界面附近电子密度的空间分布。

Characterization of a multi-keV x-ray source produced by nanosecond laser irradiation of a solid target: The influence of laser focus spot and target thickness

The influence of focus spot and target thickness on multi-keV x-ray sources generated by 2 ns duration laser heated solid targets are investigated on the Shenguang II laser facility. In the case of thick-foil targets, the experimental data and theoretical analysis show that the emission volume of the x-ray sources is sensitive to the laser focus spot and proportional to the 3 power of the focus spot size. The steady x-ray flux is proportional to the 5/3 power of the focus spot size of the given laser beam in our experimental condition. In the case of thin-foil targets, experimental data show that there is an optimal foil thickness corresponding to the given laser parameters. With the given laser beam, the optimal thin-foil thickness is proportional to the -2/3 power of the focus spot size, and the optimal x-ray energy of thin foil is independent of focus spot size. (C) 2008 American Institute of Physics.

Further acceleration of MeV electrons by a relativistic laser pulse

With the development of photocathode rf electron gun, electrons with high-brightness and mono-energy can be obtained easily. By numerically solving the relativistic equations of motion of an electron generated from this facility in laser fields modelled by a circular polarized Gaussian laser pulse, we find the electron can obtain high energy gain from the laser pulse. The corresponding acceleration distance for this electron driven by the ascending part of the laser pulse is much longer than the Rayleigh length, and the light amplitude experienced on the electron is very weak when the laser pulse overtakes the electron. The electron is accelerated effectively and the deceleration can be neglected. For intensities around 10(19) W(.)mu m(2)/cm(2), an electron's energy gain near 0.1 GeV can be realized when its initial energy is 4.5 MeV, and the final velocity of the energetic electron is parallel with the propagation axis. The energy gain can be up to 1 GeV if the intensity is about 10(21) W(.)mu m(2)/cm(2). The final energy gain of the electron as a function of its initial conditions and the parameters of the laser beam has also been discussed.

Laser beam automatic alignment in multipass amplifier

A laser beam automatic alignment system is applied in a multipass amplifier of the SG-III prototype laser. Considering the requirements of the SG-III prototype facility, by combining the general techniques of the laser beam automatic alignment system, according to the image relayed of the pinholes in the spatial filter, and utilizing the optical position and the spatial distribution of the four pinholes of the main spatial filter in the multipass amplifier of the SG-III prototype, a reasonable and optimized scheme for automatic aligning multipass beam paths is presented. It is demonstrated on the multipass amplifier experimental system. (C) 2004 Society of Photo-Optical Instrumentation Engineers.

图像处理在光路自动准直系统中的应用

光路自动准直系统应用于惯性约束聚变的高功率激光装置中的光束自动调整。图像处理是光路自动准直的关键技术之一。针对神光Ⅲ原型装置，结合阈值化、重心法、中值滤波和圆拟合等多种不同的图像处理方法设计了一套合理的准直方案，并且在模拟实验平台上进行了实验验证。实验结果表明，光路自动准直系统能够在15min之内顺利完成光路的自动调整，光束近场调整精度优于近场光斑的±0．5％，光束远场调整精度≤±0．3″，满足了原型装置的总体要求。

“神光-Ⅱ”第九路终端光学系统稳定性分析

在“神光-Ⅱ”装置上进行先进高能多功能激光束系统（简称第九路）研制工程中,由于在原ICF靶室上又增加了输入“汤姆逊探针光”和“X光背光照明探针光”的锥形真空套筒及其终端光学元件,导致原有靶室结构的变化,可能会引入新的不稳定因素.通过有限元分析方法,建立有限元分析模型,进行优化设计.通过位移传感器测量结果可知,第九路终端光学元件径向窜动所引起的打靶误差最大值为2.110 μm,小于“神光-Ⅱ”靶场终端光学系统的最大允许误差值7.785 μm.

ICF靶场中光束口径与列阵间隔的研究

从靶场反射镜架模块的机械结构设计布局所需几何空间的角度出发，根据大口径、列阵器件的特殊要求，给出符合“神光Ⅲ”装置总体技术要求的ICF靶场光束口径与列阵间隔之间的关系，得出靶场△纵、△横应满足的公式．

高功率激光装置前端系统激光脉冲的时间整形及修正技术

针对激光惯性约束聚变实验研究对高功率激光驱动器前端系统复杂时间形状种子激光脉冲的需求, 应用孔径耦合带状线集成波导整形系统设计了满足需要的前端整形激光脉冲。用一种新方法精确计算了孔径耦合带状线电脉冲整形器的耦合系数和孔径宽度的数值关系, 并针对高衬比度整形激光脉冲的需求, 提出了高衬比度双极型集成波导整形系统方案。由该系统可以得到100 ps脉冲前沿、1～3 ns脉冲宽度可调、高衬比度(大于100∶1)、光滑无纹波调制、可精确满足神光II八路及第九路装置需求的前端整形激光脉冲。

"神光-Ⅱ"装置第九路靶场终端光学组件的研制

针对“神光-Ⅱ”装置第九路系统主激光瞄准精度小于等于30μm和大焦斑辐照均匀性优于10％的要求，提出了靶场终端光学组件的设计结构。应用有限元法对组件关键机械元件和ICF靶室整体进行动静态分析，优化了设计参数。同时与聚焦透镜配合进行数值分析列阵透镜，确定了单元数、曲率和厚度以及单元长和宽等参数。经过实验测试，主激光瞄准精度达到28．9μm，大焦斑辐照的形状为1000μm×500μm，均匀性为12．0％。

ICF中可调法布里-珀罗滤波器间距稳定度研究

在神光Ⅱ第9路ICF高功率激光装置中，采用可调法布里-珀罗（F-P）滤波器对幅度调制效应进行补偿，根据补偿装置的技术要求，提出-种应用nm量级精度的电容式位移传感器对可调F-P滤波器间距稳定度进行监控的系统，详细论述了监控系统的结构与工作原理。给出了电容式位移传感器的驱动电路及数据处理与控制软件的设计方案，并对电容式位移传感器的精度进行了标定。实验结果表明，该位移监控系统能够使可调F—P滤波器的间距稳定度保持在15nm／h以内，使幅度调制效应的调制深度优于4％。

神光Ⅱ装置中空间滤波器系统的稳定性设计与分析

考虑到空间滤波器系统在激光装置中的稳定性要求，分析了影响稳定性的各种因素。对现行装置中的SF4空间滤波器系统进行振动模态测试，初步确定系统的工作状况，并结合振动理论明确系统稳定性的设计参数。利用有限元软件ANSYS对空间滤波器系统及相关的设计进行仿真验证计算。结果表明：SF4系统的一阶固有频率达到83Hz，与实验结果相符合，满足系统稳定性的要求；在系统中引入支撑不但能有效增加系统的刚度，同时能转移系统的振型；系统基础支撑平台的选择要求平台独立，并且选择较低的高度以便于控制上层光学元件的变形；在系统中的引入

大口径八边形钕玻璃片支撑系统的光机集成分析

控制由机械装夹方式所引入的波前畸变以提高惯性约束聚变(ICF)输出光束的质量，是在大口径钕玻璃片主放大器结构设计中必须考虑的。提出了一种新的有限元变形结果与光学元件面形畸变之间的数据处理方式，并与传统方式进行了对比。基于新的数据处理接口，利用光机集成分析方法对大口径八边形钕玻璃片的支撑系统结构设计参数进行优化。优化的结果保证了由支撑系统引起的透过波前畸变小于十分之一波长，同时波前畸变与设计参数变动的相关性最小。

基于棱镜实现三倍频谐波分离

基于棱镜的色散特性,提出一种楔形窗口与聚焦透镜组合的方式,解决了高功率激光装置三倍频谐波分离所存在的问题,即三倍频的高通量传输和靶面辐照。结合“神光Ⅱ”装置多功能高能激光系统有关参数进行系统设计,确定了楔形窗口参数,并对其所引起的B积分和间距误差进行了分析。通过实验测试,三倍频传输通量由0.7～1 J/cm2提高到2.8 J/cm2,同时靶面三倍频和二倍频分离间距达到2.85 mm,实现了高功率激光装置高通量传输的三倍频谐波分离。