近背向散射光诊断系统的建立对于精密测量近背向散射光能量份额具有重要意义，它为惯性约束聚变物理实验激光能量与靶耦合效率参数提供了重要的数据支撑。介绍了神光Ⅲ原型装置的近背向散射光诊断系统，包括其主要功能、技术要求、光学设计与机械设计要点。该诊断系统以离轴椭球镜及靶室外的光学传递组为核心元件，具有灵活可靠的支撑和调节结构。在原型装置上使用该系统进行了打靶试验考核，结果表明该系统能进行稳定测量，数据结果符合预期。

Development of the near backscatter light diagnostic system is important to measuring the stimulated Brillouin and stimulated Raman scatter so that the near backscatter light fraction of the ICF drive laser will be determined. Based on SG-Ⅲ prototype laser facility, a near backscatter light diagnostic system with an ellipsoidal mirror and other relay optics as core elements is designed and implemented on the facility. The whole system is well held and modulated by a portable configuration. Both the optical and mechanical design items are introduced in this paper. According to the experiment results, the system is credible and effective.