In an experiment performed on the Shenguang-III prototype laser facility, collective Thomson scattering (TS) is used to study the spatial growth of stimulated Brillouin scattering (SBS) in a gas-filled hohlraum by detecting the SBS-driven ion acoustic wave. High-quality time-resolved SBS and TS spectra are obtained simultaneously in the experiment, and these are analyzed by a steady-state code based on the ray-tracing model. The analysis indicates that ion–ion collisions may play an important role in suppressing SBS growth in the Au plasma; as a result, the SBS excited in the filled gas region is dominant. In the early phase of the laser pulse, SBS originates primarily from the high-density plasma at the edges of the interaction beam channel, which is piled up by the heating of the interaction beam. Throughout the duration of the laser pulse, the presence of the TS probe beam might mitigate SBS by perturbing the density distribution around the region overlapping with the interaction beam.

激光诱导损伤是导致熔石英真空光学元件突发破裂的根本原因。本工作采用神光-Ⅲ原型装置终端光学组件的熔石英真空光学元件制作了标准样品, 统计分析了熔石英玻璃样品表面损伤形貌特征, 探究了激光诱导损伤对熔石英玻璃样品弯曲强度的影响。结果表明: 激光诱导熔石英玻璃损伤点形貌为典型的半椭球体, 损伤点深度随其长度增大呈上升趋势, 深度极限基本不超过2 mm; 损伤点对熔石英玻璃弯曲强度影响非常明显, 含损伤点的样品平均弯曲强度仅为不含损伤点样品平均弯曲强度的41%。随着损伤点长度和深度增大, 熔石英玻璃的弯曲强度总体呈下降趋势, 但当损伤点长度大于15 mm, 弯曲强度下降趋势明显缓和, 损伤点长深比对弯曲强度无明显影响。熔石英玻璃真空窗口光学元件安全设计, 应考虑玻璃弯曲强度离散性及持久应力作用综合影响, 且在损伤点位置处的最大弯曲拉应力不应超过其弯曲强度设计值。

In indirect drive, reducing peak intensity of a single beam and controlling overlap of multi-beams are two opposite requirements for laser focal spot design. In this paper, an improved laser spot design technique for indirect drive built upon the geometric structures of laser propagation into hohlraum has been introduced. The proposed technique is able to generate appropriate continuous phase plate (CPP) producing a special shaped spot that can balance the opposite requirements. The corresponding CPP does not bring difficulties to the design and fabrication. Phase aberrations are more sensitive to the special shaped spot; however, it can be tolerable for the current beam control level.