空泡机制产生betatron X射线辐射的数值模拟

针对SILEX钛宝石激光器参数,采用PIC数值模拟程序VORPAL对激光尾波场加速进行了模拟,得到了电子轨迹及能量数据,进而通过理论计算得到了空泡机制下X射线辐射特性。结果表明,空泡机制下高能电子在空泡中做betatron振荡且多数电子被加速到170 MeV左右;加速能量较低的电子（约100 MeV）, 其辐射谱为临界能量约3 keV的类同步辐射谱,发散角约为8 mrad,而能量较高的电子（约170 MeV）对应的光子临界能量约为10 keV。     

鞘场加速机理中质子束的特性与其初始尺寸的关系

为了研究激光鞘场中质子层的尺寸对质子束特性的影响,本文应用中国工程物理研究院 激光聚变研究中心的二维Particle-In-Cell (2D-PIC)数值模拟程序Flips2D进行了相关数值模拟研究. 研究了质子束总能量随时间的变化,得出了加速持续过程与激光脉冲持续时间的关系; 研究了质子层的宽度对加速后质子束发散角和能谱的影响;研究了质子层的厚与加速后质子束 发散角和能谱的关系;得出了质子层的初始尺寸对加速后质子特性的影响规律.     

Characterization of relativistic electrons generated by a cone guiding laser pulse

We demonstrated the interaction of a gold cone target with a femto second(fs) laser pulse above the relativistic intensity of 1.37×10 18 μm 2 W/cm 2.Relativistic electrons with energy above 2 MeV were observed.A 25%-40% increase of the electron temperature is achieved compared to the case when a plane gold target is used.The electron temperature increase results from the guiding of the laser beam at the tip and the intense quasistatic magnetic field in the cone geometry.The behavior of the relativistic electrons is verified in our 2D-PIC simulations.     

Higher order harmonics suppression in extreme ultraviolet and soft x-ray

The extreme ultraviolet and soft x-ray sources are widely used in various domains. Suppressing higher order harmonics and improving spectral purity are significant. This paper describes a novel method of higher order harmonics suppression with single order diffraction gratings in extreme ultraviolet and soft x-ray. The principle of harmonic suppression with single order diffraction grating is described, and an extreme ultraviolet and soft x-ray non-harmonics grating monochromator is designed based on the single order diffraction grating. The performance is simulated by an optical design software. The emergent beams of a monochromator with different gratings are measured by a transmission grating spectrometer. The results show that the single order diffraction grating can suppress higher order harmonics effectively, and it is expected to be widely used in synchrotron radiation, diagnostics of laser induced plasma, and astrophysics.     

Single order soft X-ray diffraction with quasi-random radius pinhole array spectroscopic photon sieves

A novel single order diffraction grating in the soft X-ray region, called quasi-random radius pinhole array spectro- scopic photon sieves （QRSPS）, is proposed in this paper. This new grating is composed of pinholes on a substrate, whose radii are quasi-random, while their centers are regular. Analysis proves that its transmittance function across the grating bar is similar to that of sinusoidal transmission gratings. Simulation results show that the QRSPS can suppress higher-order diffraction effectively. And the QRSPS would still retain its characteristic of single order diffraction when we take the effect of X-ray penetration into account. These properties indicate that the QRSPS can be used in the soft X-ray spectra measurement.     

梯形透过率光栅远场光强分布及光栅方程的解析推导

二值化梯形透过率光栅是一种具有离轴衍射级次的二维光栅,其各衍射点光强信息和位置信息的确定对该新型光栅的实际应用具有重要意义。然而,目前尚无相关解析理论对其进行合理的描述。为了解决上述问题,通过二维傅里叶变换方法获得了该光栅各个衍射级次光强分布的解析表达式,并根据二维光栅的结构特征给出了在透射式和反射式情况下该光栅满足的光栅方程。这为该新型光栅的光线追迹计算打下了理论基础。最后,将解析表达式计算结果与采用X-Lab软件标量衍射模块计算的数值模拟结果进行比较,验证解析理论的正确性。     

一种新型透射式自聚焦光栅的设计及理论研究

结合普通透射光栅的分光特性和菲涅耳波带片的聚焦特性,提出一种应用于软X射线波段的新型透射式自聚焦光栅。根据菲涅耳衍射理论,对其衍射特性进行理论推导,证明该新型光栅存在一个与光栅平面垂直的焦平面,不同波长的光波聚焦于该焦平面的不同位置。在焦平面上,焦点位置随光子能量的变化是线性的,即能实现光子能量的线性测量。通过解析推导,得到在沿着焦平面和垂直于焦平面两个方向上光斑的展宽模式,发现该新型光栅在沿着焦平面的光斑展宽模式不同于普通光栅。根据基尔霍夫衍射公式,设置实用化参数,对其衍射模式进行了详细的数值模拟研究,并讨论了相应的测谱范围和谱分辨率。     

硬X射线透射晶体谱仪的设计性能参数

激光等离子体相互作用高分辨硬X射线光谱的测量通常采用柱面透射弯晶谱仪实现。利用几何光学模型对柱面透射弯晶谱仪的关键技术参数进行了理论计算和数值模拟,给出了谱仪弯晶曲率半径、光源到晶体的距离、光源尺寸和探测器的位置等因素对谱仪测谱范围和分辨能力的影响情况,分析了光谱分辨水平随能点的变化。分析结果表明:晶体曲率半径对测谱范围和谱分辨能力影响大,在光源尺寸较小时,随着探测器与罗兰圆距离的增加,谱线之间距离增加的速度大于光谱线宽增加的速度,使得分辨能力增加。     

非理想背光照相对靶壳阿贝尔密度反演的影响

建立了背光照相的模拟手段,研究了记录屏像素尺寸、背光强度分布、背光光谱非单色、针孔弥散及针孔形状对惯性约束聚变中常用塑料球壳的阿贝尔密度反演的影响。结果表明:较大的记录屏像素尺寸会掩盖密度分布的细节;高斯型的背光空间分布会使密度分布低于真实值,可能导致非物理的负密度分布;采用Mo的L带谱线作为背光源也会导致反演密度偏离真实值;当壳层厚度小于针孔尺寸时,针孔弥散效应会显著降低峰值密度,利用维纳滤波法处理背光图像后密度反演的结果得到明显改善;相同针孔面积条件下,椭圆形针孔给出的峰值密度要低于圆形针孔的结果。     

Design of Elliptical Reflection Zone Plate for Monochromatization of the Ultrafast Betatron Radiation at Low Energy Band

The elliptical reflection zone plate is a kind of optical element in soft x-ray and x-ray ranges and has focusing and dispersion properties. Compared with a transmission zone plate, the required dispersion ordei, can be easily separated from zeroth order diffraction. It is fabricated on a bulk substrate and does not have much difficulty in the fabrication process. We design a 1000-zone off-axis elliptical reflection zone plate for the rnonochromatization of the ultrafast betatron radiation at the low energy band, at the designed wavelength of 2.478 nm （500eV） which is an important spectral part of the betatron radiation, with high spatial resolution, high spectral resolution. Moreover, we simulate the designed reflection zone plate properties. The simulation results show that the spatial resolutions in the spatial direction and the spectral direction are 6.4μm and 7.3μm （full width half maximum）, respectively,, and the spectral resolution reaches up to 496 for the well aligned point source system, which is in good agreement with the theoretical predictions. In addition, we discuss some factors influencing the spectral and spatial resolution, such as the zone number, zone area and the incidence wavelength. The elliptical reflection zone plate also has potential applications in investigating x-ray fluorescence spectra and other fields.