压缩感知技术在激光惯性约束聚变研究中的应用

激光驱动惯性约束聚变（ICF）研究是当前国际前沿科学中一个具有挑战性的研究领域，它以高能激光作为驱动源，在极短的时间内将大量能量注入靶丸中使聚变材料达到高温高密度的状态从而在靶丸中心形成热斑并引燃整个燃料层，最终实现可控核聚变。由于内爆热斑直径为50～100 μm，其持续时间为100～200 ps，离子温度达到5 keV，压力可达4.0×1016 Pa。因此，发展极端瞬态条件下的诊断技术具有重要意义。介绍了两种基于压缩感知技术的诊断方法，第一种是基于数字微镜阵列（DMD）进行编码的反射式可见光压缩感知技术，这种技术将现有的一维任意反射面速度干涉仪（VISAR）与压缩超快成像（CUP）系统相结合，有望实现一种全新的具有高时间分辨的二维VISAR诊断技术，将诊断维度从一维扩展至二维，同时它克服了现有的二维VISAR单幅成像的缺点，有望实现对内爆压缩过程流体力学不稳定性演化过程的连续诊断。由于基于DMD进行编码的反射式可见光压缩感知技术只能用于可见光波段，无法用于紫外与X光波段，为此还发展了一种透射式压缩感知技术。这种透射式压缩感知技术采用一种新颖的透射式元件实现对待测信号的编码，可以实现对紫外和X光波段信号的二维超快探测，有望实现对内爆热斑超快时空演化过程进行精密诊断。此外，针对单通道CUP技术的高时间分辨的优势和低空间分辨的不足，还提出了多通道编码、分别扫描、解码、再合成的全新的高时空分辨诊断系统基本思路，有望实现高时间分辨的同时，实现高空间分辨的二维新型诊断技术。

Application of compressed sensing technology in laser inertial confinement fusion

Laser driven inertial confinement fusion is a challenging research field in the current international frontier science, which uses high-energy laser as the driving source. A large amount of energy is injected into the target pellet to make the fusion material reach the state of high temperature and high density in a very short time, thus forming a hot spot in the center of the target pellet and igniting the whole fuel layer, and finally achieving controlled nuclear fusion. As the diameter of the implosion hot spot is about 50?100 μm, and its duration is 100?200 ps, the ion temperature reaches 5 keV, and the pressure can reach 4.0×1016 Pa. Therefore, it is of great significance to develop diagnostic techniques under extreme transient conditions. In this paper we introduce two kinds of diagnosis method based on compressed sensing. The first one combines the one-dimensional line Velocity interferometer system for any reflectors (VISAR) with the Compressed Ultrafast Photography (CPU) system, which is expected to achieve a new 2D-VISAR diagnostic technique with high time resolution. At the same time, it overcomes the shortcomings of the existing two-dimensional VISAR that can only capture single image and is expected to realize continuous diagnosis of the evolution of hydrodynamic instability. Because the existing CUP technology encoded by digital micromirror device can only be used in the visible light band, and cannot be used in the ultraviolet and X-ray band, a transmission compressed sensing technology is also developed. The transmission compressed sensing technology uses a novel transmission element to encode the measured signal, which can realize the two-dimensional ultrafast detection of ultraviolet and X-ray signals, and is expected to realize the precise diagnosis of the ultra-fast space-time evolution process of the hot spots in the explosion. In addition, in view of the advantages of single-channel CUP technology with high time resolution and the shortcomings of low spatial resolution, a new high spatial resolution diagnosis system with multi-channel coding, separate scanning, decoding and re-synthesis is proposed, which is expected to achieve high time resolution and high spatial resolution of the two-dimensional new diagnostic technology.