基于源编码的高空间分辨激光等离子体X光源背光照相技术

In order to carry out research on shock wave measurement, inertial confinement fusion capsule diagnostic, equation of state measurement and Rayleigh-Taylor instability diagnostic, it needs to develop backlight radiography with high temporal and spatial resolution. Laser plasma x-ray source possess many advantages, such as short-pulse, high brightness, and tunable photon energy. However, the radiography spatial resolution is limited by source size. In spite of the spatial resolution of the 10 microns can be achieved by microstructural targets, the signal-to-noise ratio is poor because of low yield, and it is difficult to improve spatial resolution even more. A new laser plasma x-ray source backlight radiography technique based on coded source technique is present in this project. To tackle the difficulty of non-uniform spatial distribution in process of design of source coded, the project plans to study the adaptable source coded mask (the mask of uniformly redundant arrays), the inversion algorithm with strong robustness (the inversion algorithm by the forward process using coded source radiography), and single-shot monitoring techniques for the mask of source coded (diagnosing by pin-hole camera and coded aperture imaging). The experiments of source coded radiography using laser plasma x-ray source are done, to verify the technique of backlight radiography by source coded, and acquire the high spatial resolution and high signal-to-noise ratio radiography images.

开展冲击波测量、惯性约束聚变靶丸诊断、状态方程测量、Rayleigh–Taylor不稳定性诊断等研究，需要发展高时间、高空间分辨的背光照相技术。激光等离子体X光源具有短脉宽、高亮度、光子能量可调的优点，不过由于照相空间分辨受限于源尺寸。尽管采用微结构靶可实现10微米的空间分辨，但是受限于X光源产额，照相图像信噪比很低，而且空间分辨进一步提高十分困难。本项目基于源编码技术提出一种新型等离子体X光源背光照相技术。为解决X光源空间分布不均匀性时的源编码设计困难，拟研究适应性好的源编码模式（均匀冗余阵列等模式）、鲁棒性强的反演算法（基于编码源照相正过程反演算法）与单发源编码模式监测技术（针孔相机、编码孔成像等诊断工具）。开展激光等离子体X光源源编码照相实验，验证源编码背光照相技术，获得高空间分辨、高信噪比的照相图像。

为建立惯性约束聚变（ICF）内爆、冲击波测量等高分辨背光照相技术，项目开展了激光X射线源编码设计与实验研究。首先设计了适用于激光X射线的源编码模式，建立了反演算法，设计的编码模式与反演算法具有较强的鲁棒性，能适应实验因素的影响。在星光III、神光II升级激光装置上开展了X射线源编码实验，获得了源编码靶源区分布、光子产额、照相空间分辨等关键参数，排丝靶的源编码照相结果在一维上已经实现接近单丝的极限空间分辨（直径12μm），优于直径20 μm单丝靶的结果，在康普顿照相X射线能段（50-200keV），排丝靶的激光转换效率接近直径20μm单丝靶，是同直径单丝靶的2倍，验证了源编码技术能提高X射线光源产额，并保持高照相空间分辨率。X射线源模拟与设计中建立了基于深度优先合并方法的复杂源分布定义模拟方法，实现了源编码照相的高效模拟；同时建立了透视照相中光子能量优化方法，为源编码照相用于动态过程奠定了基础。发展了X射线照相与能谱测量技术，实验测量了CsI针状屏等X射线成像探测器空间分辨率；同时研制了滤片堆栈谱仪，设计了基于前冲康普顿电子的高能伽马能谱测量系统，为激光X射线源、伽马源能谱高精度测量奠定了基础。