神光-Ⅲ主机近背向散射诊断光学系统设计

通过分析激光聚变中近背向散射光的收集方式，提出了采用金属环形椭球镜有效收集神光-Ⅲ主机装置的近背向散射光并测量其能量份额的方法。给出了椭球镜参数的设计方法。大口径椭球镜采用4块拼接形式，便于进入入口为φ1.0 m的靶室；镜体采用超硬铝材、三角形减重槽设计，实现了高稳定性、轻量化。介绍了光学系统总体结构，并对其集光效果进行了模拟评价。分析了镜体设计中的关键问题，并提出采用点激光器阵列进行中间过程面形监测的方法，避免了工序反复。分析了系统杂散光来源，采取了物理隔离、光学吸收和滤光片过滤等措施降低杂散光干扰。研制的环形椭球镜外径为1 200 mm，内径为400 mm，最大离轴量为1 411 mm，最大厚度为67 mm，重量约为48 kg；对5 mm的物方视场，像点光斑大小约为φ1.2 mm。实验显示该近背向散射诊断系统可满足神光-Ⅲ主机背向散射诊断的需求。

Design of optical system for SG-Ⅲ near backscatter diagnosis

After analysis the collecting methods of near backscatter light in laser fusion, a metal ellipsoidal mirror was proposed to collect the near backscatter light of SG-Ⅲ laser facility. Then, the method to determine the parameters of ellipsoidal mirror was discussed. The mirror is composed of four pieces, which makes it entering into the target chamber easily. The mirror is made of super hard aluminum, and a triangular weight reducing slot is designed on the back of the mirror to reduce its weight and improve its mechanical stability. The overall structure of the optical system was introduced, and the light gathering performance was simulated using optical software. The key issues in ellipsoidal mirror design, including material selection and structure selection, were analyzed. In order to avoid rework, a semiconductor laser array was developed specially to test the surface in design processing. The stray lights in the system were analyzed, physical isolation, optical absorbing and optical filters were used to control them. The ring ellipsoidal mirror with a weight of 48 kg has an outside diameter of 1 200 mm, an inside diameter of 400 mm, the maximum off-axis magnitude of 1 411 mm, and the maximum thickness of 67 mm. The image spot size is about 1.2 mm within a field of view 5 mm. This system mentioned above can offer a reference for near backscatter diagnostic in inertial confinement fusion research.