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激光等离子体不稳定性（ LPI）是惯性约束聚变（ ICF）点火过程中的关键问题之一， 多年来受到了广泛的关注。其中， 宽带激光被认为是解决 LPI 问题的一个有效途径，并且目前已经有了大量的模拟研究和少量背向、近前向散射的实验研究， 但是仍然需要侧向散射的实验研究作为补充。因此， 基于输出达到数百焦耳的宽带二倍频激光装置—“昆吾”，本文针对宽带激光与传统窄带激光与驱动平面厚靶产生的等离子体不稳定性的侧向散射以及超热电子产额设计实验。实验结果表明， 功率密度为 1×1015W·cm-2 的宽带激光激发的侧向受激布里渊散射（ SBS） 与侧向受激拉曼散射（ SRS） 在不同角度下的光谱和份额与窄带激光存在显著差异。进一步分析发现， 宽带条件下侧向的超热电子份额整体要高于窄带， 而此时宽带条件下小角度近前向、小角度近背向的 SRS 份额却远低于窄带，初步的定性分析认为此时 SRS 可能不是超热电子的主要产生机制， 认为此时可能是 PDI 对超热电子的产生起了主导作用。
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关键词:
- 激光等离子体不稳定性(LPI) /
- 宽带激光 /
- 超热电子
Laser-plasma instability (LPI) is one of the key issues in the ignition process of inertial confinement fusion (ICF), and extensive theoretical, simulation, and experimental research has been conducted over the years. Broadband laser, due to its low temporal coherence, can reduce the effective electric field strength when interacting with plasma and disrupt the phase-matching conditions of LPI, thus considered an effective approach to solving LPI issues. Current extensive simulation studies indicate that broadband laser can suppress the generation of phenomena such as Stimulated Brillouin Scattering (SBS), Stimulated Raman Scattering (SRS), and Two-Plasmon Decay (TPD) to some extent. There are also a few backward scattering experimental studies, but more experimental research such as side-scattering is still needed. Therefore, based on the broadband second harmonic laser facility “Kunwu”, this paper designs experiments for the lateral scattering of critical density plasma driven by broadband and traditional narrowband lasers, as well as the production of hot electrons. The experimental results show that the side SBS and side SRS spectra and shares at different angles excited by broadband lasers with a power density of 1×1015W·cm-2 have significant differences from those of narrowband lasers. Further analysis reveals that the overall share of hot electrons in the lateral direction is higher for broadband lasers compared to narrowband lasers. However, under broadband conditions, the share of SRS at small forward and backward angles is significantly lower than that of narrowband lasers. Preliminary qualitative analysis suggests that SRS may not be the primary mechanism for hot electron generation in this case, and that PDI might play a dominant role in the generation of hot electrons.-
Keywords:
- Laser plasma instability (LPI) /
- Broadband laser /
- hot electron
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